IgA dominates the early neutralizing antibody response to SARS-CoV-2

Long-term adaptive response in COVID-19 vaccine recipients and the effect of a booster dose

We examined the immune response in subjects previously infected with SARS-CoV2 and infection-naïve 9 months after primary 2-dose COVID-19 mRNA vaccination and 3 months after the booster dose in a longitudinal cohort of healthcare workers. Nine months after primary vaccination, previously infected subjects exhibited higher residual antibody levels, with significant neutralizing activity against distinct variants compared to infection-naïve subjects. The higher humoral response was associated with higher levels of receptor binding domain (RBD)-specific IgG⁺ and IgA⁺ memory B cells. The booster dose increased neither neutralizing activity, nor the B and T cell frequencies. Conversely, infection-naïve subjects needed the booster to achieve comparable levels of neutralizing antibodies as those found in previously infected subjects after primary vaccination. The neutralizing titer correlated with anti-RBD IFNγ producing T cells, in the face of sustained B cell response. Notably, pre-pandemic samples showed high Omicron cross-reactivity. These data show the importance of the booster dose in reinforcing immunological memory and increasing circulating antibodies in infection-naïve subjects.

Immune correlates of protection for SARS-CoV-2, Ebola and Nipah virus infection

Correlates of protection (CoP) are biological parameters that predict a certain level of protection against an infectious disease. Well-established correlates of protection facilitate the development and licensing of vaccines by assessing protective efficacy without the need to expose clinical trial participants to the infectious agent against which the vaccine aims to protect. Despite the fact that viruses have many features in common, correlates of protection can vary considerably amongst the same virus family and even amongst a same virus depending on the infection phase that is under consideration. Moreover, the complex interplay between the various immune cell populations that interact during infection and the high degree of genetic variation of certain pathogens, renders the identification of immune correlates of protection difficult. Some emerging and re-emerging viruses of high consequence for public health such as SARS-CoV-2, Nipah virus (NiV) and Ebola virus (EBOV) are especially challenging with regards to the identification of CoP since these pathogens have been shown to dysregulate the immune response during infection. Whereas, virus neutralising antibodies and polyfunctional T-cell responses have been shown to correlate with certain levels of protection against SARS-CoV-2, EBOV and NiV, other effector mechanisms of immunity play important roles in shaping the immune response against these pathogens, which in turn might serve as alternative correlates of protection. This review describes the different components of the adaptive and innate immune system that are activated during SARS-CoV-2, EBOV and NiV infections and that may contribute to protection and virus clearance. Overall, we highlight the immune signatures that are associated with protection against these pathogens in humans and could be used as CoP.

A spatially resolved atlas of the human lung characterizes a gland-associated immune niche

Single-cell transcriptomics has allowed unprecedented resolution of cell types/states in the human lung, but their spatial context is less well defined. To (re)define tissue architecture of lung and airways, we profiled five proximal-to-distal locations of healthy human lungs in depth using multi-omic single cell/nuclei and spatial transcriptomics (queryable at lungcellatlas.org ). Using computational data integration and analysis, we extend beyond the suspension cell paradigm and discover macro and micro-anatomical tissue compartments including previously unannotated cell types in the epithelial, vascular, stromal and nerve bundle micro-environments. We identify and implicate peribronchial fibroblasts in lung disease. Importantly, we discover and validate a survival niche for IgA plasma cells in the airway submucosal glands (SMG). We show that gland epithelial cells recruit B cells and IgA plasma cells, and promote longevity and antibody secretion locally through expression of CCL28, APRIL and IL-6. This new 'gland-associated immune niche' has implications for respiratory health.

Respiratory mucosal vaccination of peptide-poloxamine-DNA nanoparticles provides complete protection against lethal SARS-CoV-2 challenge

The ongoing SARS-CoV-2 pandemic represents a brutal reminder of the continual threat of mucosal infectious diseases. Mucosal immunity may provide robust protection at the predominant sites of SARS-CoV-2 infection. However, it remains unclear whether respiratory mucosal administration of DNA vaccines could confer protective immune responses against SARS-CoV-2 challenge due to insurmountable barriers posed by the airway. Here, we applied self-assembled peptide-poloxamine nanoparticles with mucus-penetrating properties for pulmonary inoculation of a COVID-19 DNA vaccine (pSpike/PP-sNp). The pSpike/PP-sNp not only displays superior gene transfection and favorable biocompatibility in the mouse airway, but also promotes a tripartite immunity consisting of systemic, cellular, and mucosal immune responses that are characterized by mucosal IgA secretion, high levels of neutralizing antibodies, and resident memory phenotype T-cell responses in the lungs of mice. Most importantly, immunization with pSpike/PP-sNp completely eliminates SARS-CoV-2 infection in both upper and lower respiratory tracts and enables 100% survival rate of mice following lethal SARS-CoV-2 challenge. Our findings indicate PP-sNp is a promising platform in mediating DNA vaccines to elicit all-around mucosal immunity against SARS-CoV-2.

Safety and immunogenicity of heterologous and homologous inactivated and adenoviral-vectored COVID-19 vaccine regimens in healthy adults: a prospective cohort study

In light of intermittent supply shortages of individual vaccines and evidence of rare but serious adverse events after vaccination, heterologous regimens for COVID-19 vaccines have gained significant interest. This study aims to assess the reactogenicity and immunogenicity of the heterologous adenoviral vector (ChAdOx1-S, AstraZeneca; hereafter referred to as AZ) and the inactivated vaccine regimen (CoronaVac; hereafter referred to as CV) in healthy Thai adults immunized between June and September 2021. Our study showed that adverse events following homologous CV-CV and AZ-AZ, and heterologous CV-AZ and AZ-CV combinations, were mild and well tolerated overall. Receptor-binding domain (RBD)-specific antibody responses and neutralizing activities against wild-type and variants of concern after two-dose vaccination were higher in the heterologous CV-AZ and homologous AZ-AZ groups compared to the CV-CV and AZ-CV groups. Conversely, the spike-specific IgA response was detected only in the CV-AZ group after two doses of vaccination. The total interferon gamma response was detected in both the CV-AZ and AZ-CV groups after the two-dose vaccination. Given the shorter completion time of two doses, heterologous CoronaVac followed by ChAdOx1-S can be considered as an alternative regimen to homologous efficacy-proven ChAdOx1-S in countries with circulating variants. Additional studies on the efficacy and durability of immune responses induced by heterologous vaccine regimens are warranted.

Neutralizing antibodies against SARS-CoV-2 are higher but decline faster in mRNA vaccinees compared to individuals with natural infection

BACKGROUND

Waning protection against emerging SARS-CoV-2 variants by pre-existing antibodies elicited because of current vaccination or natural infection is a global concern. Whether this is due to the waning of immunity to SARS-COV-2 remains unclear.

AIM

We aimed to investigate the dynamics of antibody isotype responses amongst vaccinated naïve (VN) and naturally infected (NI) individuals.

METHODS

We followed up antibody levels in COVID-19 messenger RNA (mRNA)-vaccinated subjects without prior infection (VN, n = 100) in two phases: phase-I (P-I) at ~ 1.4 and phase-II (P-II) at ~ 5.3 months. Antibody levels were compared with those of unvaccinated and naturally infected subjects (NI, n = 40) at ~ 1.7 (P-1) and 5.2 (P-II) months post-infection. Neutralizing antibodies (NTAb), anti-S-RBD-IgG, -IgM and anti-S-IgA isotypes were measured.

RESULTS

The VN group elicited significantly greater antibody responses (P < 0.001) than the NI group at P-I, except for IgM. In the VN group, a significant waning in antibody response was observed in all isotypes. There was about an ~ 4-fold decline in NTAb levels (P < 0.001), anti-S-RBD-IgG (~5-fold, P < 0.001), anti-S-RBD-IgM (~6-fold, P < 0.001) and anti-S1-IgA (2-fold, P < 0.001). In the NI group, a significant but less steady decline was notable in S-RBD-IgM (~2-fold, P < 0.001), and a much smaller but significant difference in NTAb (<2-fold, P < 0.001) anti-S-RBD IgG (<2-fold, P = 0.005). Unlike the VN group, the NI group mounted a lasting anti-S1-IgA response with no significant decline. Anti-S1-IgA, which were ~ 3-fold higher in VN subjects compared with NI in P-1 (P < 0.001), dropped to almost the same levels, with no significant difference observed between the two groups in P-II.

CONCLUSION

Whereas double-dose mRNA vaccination boosted antibody levels, vaccinated individuals' 'boost' was relatively short-lived.

An Immunological Review of SARS-CoV-2 Infection and Vaccine Serology: Innate and Adaptive Responses to mRNA, Adenovirus, Inactivated and Protein Subunit Vaccines

The coronavirus disease 2019 (COVID-19) pandemic is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, which is defined by its positive-sense single-stranded RNA (ssRNA) structure. It is in the order Nidovirales, suborder Coronaviridae, genus Betacoronavirus, and sub-genus Sarbecovirus (lineage B), together with two bat-derived strains with a 96% genomic homology with other bat coronaviruses (BatCoVand RaTG13). Thus far, two Alphacoronavirus strains, HCoV-229E and HCoV-NL63, along with five Betacoronaviruses, HCoV-HKU1, HCoV-OC43, SARS-CoV, MERS-CoV, and SARS-CoV-2, have been recognized as human coronaviruses (HCoVs). SARS-CoV-2 has resulted in more than six million deaths worldwide since late 2019. The appearance of this novel virus is defined by its high and variable transmission rate (RT) and coexisting asymptomatic and symptomatic propagation within and across animal populations, which has a longer-lasting impact. Most current therapeutic methods aim to reduce the severity of COVID-19 hospitalization and virus symptoms, preventing the infection from progressing from acute to chronic in vulnerable populations. Now, pharmacological interventions including vaccines and others exist, with research ongoing. The only ethical approach to developing herd immunity is to develop and provide vaccines and therapeutics that can potentially improve on the innate and adaptive system responses at the same time. Therefore, several vaccines have been developed to provide acquired immunity to SARS-CoV-2 induced COVID-19-disease. The initial evaluations of the COVID-19 vaccines began in around 2020, followed by clinical trials carried out during the pandemic with ongoing population adverse effect monitoring by respective regulatory agencies. Therefore, durability and immunity provided by current vaccines requires further characterization with more extensive available data, as is presented in this paper. When utilized globally, these vaccines may create an unidentified pattern of antibody responses or memory B and T cell responses that need to be further researched, some of which can now be compared within laboratory and population studies here. Several COVID-19 vaccine immunogens have been presented in clinical trials to assess their safety and efficacy, inducing cellular antibody production through cellular B and T cell interactions that protect against infection. This response is defined by virus-specific antibodies (anti-N or anti-S antibodies), with B and T cell characterization undergoing extensive research. In this article, we review four types of contemporary COVID-19 vaccines, comparing their antibody profiles and cellular aspects involved in coronavirus immunology across several population studies.

Characterization of Systemic and Mucosal Humoral Immune Responses to an Adjuvanted Intranasal SARS-CoV-2 Protein Subunit Vaccine Candidate in Mice

Continuous viral evolution of SARS-CoV-2 has resulted in variants capable of immune evasion, vaccine breakthrough infections and increased transmissibility. New vaccines that invoke mucosal immunity may provide a solution to reducing virus transmission. Here, we evaluated the immunogenicity of intranasally administered subunit protein vaccines composed of a stabilized SARS-CoV-2 spike trimer or the receptor binding domain (RBD) adjuvanted with either cholera toxin (CT) or an archaeal lipid mucosal adjuvant (AMVAD). We show robust induction of immunoglobulin (Ig) G and IgA responses in plasma, nasal wash and bronchoalveolar lavage in mice only when adjuvant is used in the vaccine formulation. While the AMVAD adjuvant was more effective at inducing systemic antibodies against the RBD antigen than CT, CT was generally more effective at inducing overall higher IgA and IgG titers against the spike antigen in both systemic and mucosal compartments. Furthermore, vaccination with adjuvanted spike led to superior mucosal IgA responses than with the RBD antigen and produced broadly targeting neutralizing plasma antibodies against ancestral, Delta and Omicron variants in vitro; whereas adjuvanted RBD elicited a narrower antibody response with neutralizing activity only against ancestral and Delta variants. Our study demonstrates that intranasal administration of an adjuvanted protein subunit vaccine in immunologically naïve mice induced both systemic and mucosal neutralizing antibody responses that were most effective at neutralizing SARS-CoV-2 variants when the trimeric spike was used as an antigen compared to RBD.

SARS-CoV-2-Neutralizing Humoral IgA Response Occurs Earlier but Is Modest and Diminishes Faster than IgG Response

Secretory immunoglobulin A (IgA) plays a crucial role in mucosal immunity for preventing the invasion of exogenous antigens; however, little is understood about the neutralizing activity of serum IgA. Here, to examine the role of IgA antibodies against COVID-19 illnesses, we determined the neutralizing activity of serum/plasma IgG and IgA purified from previously SARS-CoV-2-infected and COVID-19 mRNA vaccine-receiving individuals. We found that serum/plasma IgA possesses substantial but rather modest neutralizing activity against SARS-CoV-2 compared to IgG with no significant correlation with the disease severity. Neutralizing IgA and IgG antibodies achieved the greatest activity at approximately 25 and 35 days after symptom onset, respectively. However, neutralizing IgA activity quickly diminished to below the detection limit approximately 70 days after onset, while substantial IgG activity was observed until 200 days after onset. The total neutralizing activity in sera/plasmas of those with COVID-19 largely correlated with those in purified IgG and purified IgA and levels of anti-SARS-CoV-2-S1-binding IgG and anti-SARS-CoV-2-S1-binding IgA. In individuals who were previously infected with SARS-CoV-2 but had no detectable neutralizing IgA activity, a single dose of BNT162b2 or mRNA-1273 elicited potent serum/plasma-neutralizing IgA activity, but the second dose did not further strengthen the neutralization antibody response. The present data show that the systemic immune stimulation with natural infection and COVID-19 mRNA-vaccines elicits both SARS-CoV-2-specific neutralizing IgG and IgA responses in serum, but the IgA response is modest and diminishes faster than the IgG response. IMPORTANCE Secretory dimeric immunoglobulin A (IgA) plays an important role in preventing the invasion of foreign objects by its neutralizing activity on mucosal surfaces, while monomeric serum IgA is thought to relate to the phagocytic immune system activation. Here, we report that individuals with the novel coronavirus disease (COVID-19) developed both systemic neutralizing IgG (nIgG) and IgA (nIgA) active against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although the nIgA response was quick and reached the highest activity earlier than the nIgG response, nIgA activity was modest and diminished faster than nIgG activity. In individuals who recovered from COVID-19 but had no detectable nIgA activity, a single dose of COVID-19 mRNA vaccine elicited potent nIgA activity, but the second dose did not further strengthen the antibody response. Our study provides novel insights into the role and the kinetics of serum nIgA against the pathogen in both naturally infected and COVID-19 mRNA vaccine-receiving COVID-19-convalescent individuals.

Full-Lung Prophylaxis against SARS-CoV-2 by One-Shot or Booster Intranasal Lentiviral Vaccination in Syrian Golden Hamsters

Following the breakthrough of numerous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants in recent months and the incomplete efficiency of the currently available vaccines, development of more effective vaccines is desirable. Non-integrative, non-cytopathic and non-inflammatory lentiviral vectors elicit sterilizing prophylaxis against SARS-CoV-2 in preclinical animal models and are particularly suitable for mucosal vaccination, which is acknowledged as the most effective in reducing viral transmission. Here, we demonstrate that a single intranasal administration of a vaccinal lentiviral vector encoding a stabilized form of the original SARS-CoV-2 Spike glycoprotein induces full-lung protection of respiratory tracts and strongly reduces pulmonary inflammation in the susceptible Syrian golden hamster model against the prototype SARS-CoV-2. In addition, we show that a lentiviral vector encoding stabilized Spike of SARS-CoV-2 Beta variant (LV::S_Beta-2P) prevents pathology and reduces infectious viral loads in lungs and nasal turbinates following inoculation with the SARS-CoV-2 Omicron variant. Importantly, an intranasal boost with LV::S_Beta-2P improves cross-seroneutralization much better in LV::S_Beta-2P-primed hamsters than in their counterparts primed with an LV-encoding Spike from the ancestral SARS-CoV-2. These results strongly suggest that an immune imprint with the original Spike sequence has a negative impact on cross-protection against new variants. Our results tackle the issue of vaccine effectiveness in people who have already been vaccinated and have vanished immunity and indicate the efficiency of LV-based intranasal vaccination, either as a single dose or as booster.

Longitudinal analysis of serum neutralization of SARS-CoV-2 Omicron BA.2, BA.4, and BA.5 in patients receiving monoclonal antibodies

The emergence of Omicron sublineages impacts the therapeutic efficacy of anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) monoclonal antibodies (mAbs). Here, we evaluate neutralization and antibody-dependent cellular cytotoxicity (ADCC) activities of 6 therapeutic mAbs against Delta, BA.2, BA.4, and BA.5. The Omicron subvariants escape most antibodies but remain sensitive to bebtelovimab and cilgavimab. Consistent with their shared spike sequence, BA.4 and BA.5 display identical neutralization profiles. Sotrovimab is the most efficient at eliciting ADCC. We also analyze 121 sera from 40 immunocompromised individuals up to 6 months after infusion of Ronapreve (imdevimab + casirivimab) or Evusheld (cilgavimab + tixagevimab). Sera from Ronapreve-treated individuals do not neutralize Omicron subvariants. Evusheld-treated individuals neutralize BA.2 and BA.5, but titers are reduced. A longitudinal evaluation of sera from Evusheld-treated patients reveals a slow decay of mAb levels and neutralization, which is faster against BA.5. Our data shed light on antiviral activities of therapeutic mAbs and the duration of effectiveness of Evusheld pre-exposure prophylaxis.

Neutrophil profiles of pediatric COVID-19 and multisystem inflammatory syndrome in children

Multisystem inflammatory syndrome in children (MIS-C) is a delayed-onset, COVID-19-related hyperinflammatory illness characterized by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigenemia, cytokine storm, and immune dysregulation. In severe COVID-19, neutrophil activation is central to hyperinflammatory complications, yet the role of neutrophils in MIS-C is undefined. Here, we collect blood from 152 children: 31 cases of MIS-C, 43 cases of acute pediatric COVID-19, and 78 pediatric controls. We find that MIS-C neutrophils display a granulocytic myeloid-derived suppressor cell (G-MDSC) signature with highly altered metabolism that is distinct from the neutrophil interferon-stimulated gene (ISG) response we observe in pediatric COVID-19. Moreover, we observe extensive spontaneous neutrophil extracellular trap (NET) formation in MIS-C, and we identify neutrophil activation and degranulation signatures. Mechanistically, we determine that SARS-CoV-2 immune complexes are sufficient to trigger NETosis. Our findings suggest that hyperinflammatory presentation during MIS-C could be mechanistically linked to persistent SARS-CoV-2 antigenemia, driven by uncontrolled neutrophil activation and NET release in the vasculature.

In Vitro Diagnostic Assay to Detect SARS-CoV-2-Neutralizing Antibody in Patient Sera Using Engineered ACE-2 Mini-Protein

The recent development and mass administration of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) vaccines allowed for disease control, reducing hospitalizations and mortality. Most of these vaccines target the SARS-CoV-2 Spike (S) protein antigens, culminating with the production of neutralizing antibodies (NAbs) that disrupt the attachment of the virus to ACE2 receptors on the host cells. However, several studies demonstrated that the NAbs typically rise within a few weeks after vaccination but quickly reduce months later. Thus, multiple booster administration is recommended, leading to vaccination hesitancy in many populations. Detecting serum anti-SARS-CoV-2 NAbs can instruct patients and healthcare providers on correct booster strategies. Several in vitro diagnostics kits are available; however, their high cost impairs the mass NAbs diagnostic testing. Recently, we engineered an ACE2 mimetic that interacts with the Receptor Binding Domain (RBD) of the SARS-2 S protein. Here we present the use of this engineered mini-protein (p-deface2 mut) to develop a detection assay to measure NAbs in patient sera using a competitive ELISA assay. Serum samples from twenty-one patients were tested. Nine samples (42.8%) tested positive, and twelve (57.1%) tested negative for neutralizing sera. The data correlated with the result from the standard commercial assay that uses human ACE2 protein. This confirmed that p-deface2 mut could replace human ACE2 in ELISA assays. Using bacterially expressed p-deface2 mut protein is cost-effective and may allow mass SARS-CoV-2 NAbs detection, especially in low-income countries where economical diagnostic testing is crucial. Such information will help providers decide when a booster is required, reducing risks of reinfection and preventing the administration before it is medically necessary.

The long-term dynamics of serum antibodies against SARS-CoV-2

Objective

To analyze the long-term dynamics of antibodies against SARS-CoV-2 and understand the impact of age, gender, and viral load on patients' immunological response.

Methods

Serum samples were obtained from 231 COVID-19 positive patients from Macaé, in Rio de Janeiro state, in Brazil, from June 2020 until January 2021. The production of IgA, IgM, IgG, and IgE against S glycoprotein was analyzed using the S-UFRJ assay, taking into account the age, gender, and viral load.

Results

Analysis of antibody production over 7 months revealed that IgA positivity gradually decreased after the first month. Additionally, the highest percentage of IgM positivity occurred in the first month (97% of patients), and declined after this period, while IgG positivity remained homogeneous for all 7 months. The same analysis for IgE revealed that almost all samples were negative. The comparison of antibody production between genders showed no significant difference. Regarding the age factor and antibody production, patients aged ≥60 years produced almost twice more IgA than younger ones (17-39 years old). Finally, a relationship between viral load and antibody production was observed only for older patients.

Conclusions

Our work provides an overview of long-term production of antibodies against SARS-CoV-2, suggesting prolonged production of IgA and IgM antibodies for 3 months and continued IgG production for over 7 months. In addition, it identified a correlation between viral load and IgM titers in the older group and, finally, different IgA production between the age groups.

Milk antibody response after 3rd dose of COVID-19 mRNA vaccine and SARS-CoV-2 breakthrough infection and implications for infant protection

Anti-SARS-CoV-2 antibodies have been found in human-milk after COVID-19 infection and vaccination. However, little is known about their persistence in milk after booster vaccination and breakthrough infection. In this study, human-milk, saliva and blood samples were collected from 33 lactating individuals before and after mRNA-based vaccination and COVID-19 breakthrough infections. Antibody levels were measured using ELISA and symptoms were assessed using questionnaires. Evaluation of maternal and infant symptomatology revealed that infected mothers reported more symptoms than vaccinated mothers. We found that after vaccination, human-milk anti-SARS-CoV-2 antibodies persisted for up to 8 months. In addition, distinct patterns of human milk IgA and IgG production we observed after breakthrough infection compared to 3-dose vaccination series alone, indicating a differential central and mucosal immune profiles in hybrid compared with vaccine-induced immunity. To investigate passively-derived milk antibody protection in infants, we examined the persistence of these antibodies in infant saliva after breastfeeding. We found that IgA was more abundant in infant saliva compared to IgG and persist in infant saliva longer after feeding. Our results delineate the differences in milk antibody response to vaccination as compared to breakthrough infection and emphasize the importance of improving the secretion of IgA antibodies to human milk after vaccination to improve the protection of breastfeeding infants.

Duration of BA.5 neutralization in sera and nasal swabs from SARS-CoV-2 vaccinated individuals, with or without omicron breakthrough infection

BACKGROUND

Since early 2022, Omicron BA.1 has been eclipsed by BA.2, which was in turn outcompeted by BA.5, which displays enhanced antibody escape properties.

METHODS

Here, we evaluated the duration of the neutralizing antibody (Nab) response, up to 18 months after Pfizer BNT162b2 vaccination, in individuals with or without BA.1/BA.2 breakthrough infection. We measured neutralization of the ancestral D614G lineage, Delta, and Omicron BA.1, BA.2, and BA.5 variants in 300 sera and 35 nasal swabs from 27 individuals.

FINDINGS

Upon vaccination, serum Nab titers were decreased by 10-, 15-, and 25-fold for BA.1, BA.2, and BA.5, respectively, compared with D614G. We estimated that, after boosting, the duration of neutralization was markedly shortened from 11.5 months with D614G to 5.5 months with BA.5. After breakthrough, we observed a sharp increase of Nabs against Omicron subvariants, followed by a plateau and a slow decline after 5-6 months. In nasal swabs, infection, but not vaccination, triggered a strong immunoglobulin A (IgA) response and a detectable Omicron-neutralizing activity.

CONCLUSIONS

BA.5 spread is partly due to abbreviated vaccine efficacy, particularly in individuals who were not infected with previous Omicron variants.

FUNDING

Work in O.S.'s laboratory is funded by the Institut Pasteur, Urgence COVID-19 Fundraising Campaign of Institut Pasteur, Fondation pour la Recherche Médicale (FRM), ANRS, the Vaccine Research Institute (ANR-10-LABX-77), Labex IBEID (ANR-10-LABX-62-IBEID), ANR/FRM Flash Covid PROTEO-SARS-CoV-2, ANR Coronamito, and IDISCOVR, Laboratoire d'Excellence 'Integrative Biology of Emerging Infectious Diseases' (grant no. ANR-10-LABX-62-IBEID), HERA european funding and the NIH PICREID (grant no U01AI151758).

B-Cell Responses to Sars-Cov-2 mRNA Vaccines

Most vaccines against viral pathogens protect through the acquisition of immunological memory from long-lived plasma cells that produce antibodies and memory B cells that can rapidly respond upon an encounter with the pathogen or its variants. The COVID-19 pandemic and rapid deployment of effective vaccines have provided an unprecedented opportunity to study the immune response to a new yet rapidly evolving pathogen. Here we review the scientific literature and our efforts to understand antibody and B-cell responses to SARS-CoV-2 vaccines, the effect of SARSCoV-2 infection on both primary and secondary immune responses, and how repeated exposures may impact outcomes.

Preclinical evaluation of safety and immunogenicity of a primary series intranasal COVID-19 vaccine candidate (BBV154) and humoral immunogenicity evaluation of a heterologous prime-boost strategy with COVAXIN (BBV152)

Most if not all vaccine candidates developed to combat COVID-19 due to SARS-CoV-2 infection are administered parenterally. As SARS-CoV-2 is transmitted through infectious respiratory fluids, vaccine-induced mucosal immunity could provide an important contribution to control this pandemic. ChAd-SARS-CoV-2-S (BBV154), a replication-defective chimpanzee adenovirus (ChAd)-vectored intranasal (IN) COVID-19 vaccine candidate, encodes a prefusion-stabilized version of the SARS-CoV-2 spike protein containing two proline substitutions in the S2 subunit. We performed preclinical evaluations of BBV154 in mice, rats, hamsters and rabbits. Repeated dose toxicity studies presented excellent safety profiles in terms of pathology and biochemical analysis. IN administration of BBV154 elicited robust mucosal and systemic humoral immune responses coupled with Th1 cell-mediated immune responses. BBV154 IN vaccination also elicited potent variant (omicron) cross neutralization antibodies. Assessment of anti-vector (ChAd36) neutralizing antibodies following repeated doses of BBV154 IN administration showed insignificant titers of ChAd36 neutralizing antibodies. However, the immune sera derived from the same animals displayed significantly higher levels of SARS-CoV-2 virus neutralization (p<0.003). We also evaluated the safety and immunogenicity of heterologous prime-boost vaccination with intramuscular (IM) COVAXIN-prime followed by BBV154 IN administration. COVAXIN priming followed by BBV154 IN-booster showed an acceptable reactogenicity profile comparable to the homologous COVAXIN/COVAXIN or BBV154/BBV154 vaccination model. Heterologous vaccination of COVAXIN-prime and BBV154 booster also elicited superior (p<0.005) and cross variant (omicron) protective immune responses (p<0.013) compared with the homologous COVAXIN/COVAXIN schedule. BBV154 has successfully completed both homologous and heterologous combination schedules of human phase 3 clinical trials and received the restricted emergency use approval (in those aged above 18 years) from the Drugs Controller General of India (DCGI).

SARS-CoV-2 spike RBD-specific IgA and IgG antibodies in breast milk after vaccination with the protein subunit vaccine Abdala

Background

COVID-19 vaccines that trigger a strong secretory antibody response in breast milk may achieve effective passive protection of vulnerable newborns and breastfed infants of immunized mothers. The aim of this work was to investigate the presence of SARS-CoV-2 spike RBD-specific IgA and IgG antibodies in breast milk, 5 and 9 weeks after vaccination with 3 doses of the protein subunit vaccine Abdala, compared to those found in breast milk from COVID-19-recovered women, collected at least 40 days after the infection.

Methods

SARS-CoV-2 spike RBD-specific IgA and IgG antibodies were semi-quantified by indirect ELISA, using a homemade standard generated by pooling twenty breast milk samples with high absorbance values according to preliminary data. The validity of the standard curves was proved following the European Medicines Agency Guideline. Two breast milk samples from 2 unvaccinated women who had not been infected with COVID-19 were included as negative controls. Potentially neutralizing antibodies was assessed by a SARS-CoV-2 surrogate virus neutralization test.

Results

High levels of anti-RBD IgA antibodies were detected in breast milk samples 9 weeks after vaccination and anti-RBD IgG antibodies rise from the fifth to the ninth week. In the post-COVID-19 time that was evaluated, the IgG-type response was notably higher compared to both post-vaccination periods. Neutralizing antibody titers were similar in breast milk from vaccinated and COVID-19 recovered women.

Conclusions

This is the first report about the immune response in breast milk after the administration of a COVID-19 protein subunit vaccine, which could provide analogous protection to that conferred by SARS-CoV-2 infection. This implies a potential passive immunity that breastfed infants receive from their mothers vaccinated with Abdala.

Genome-wide association studies of COVID-19: Connecting the dots

Genome-wide association studies (GWASs) are a research approach used to identify genetic variants associated with common diseases, like COVID-19. The lead genetic variants (n = 41) reported by the eleven largest COVID-19 GWASs are mapped to 22 different chromosomal regions. The loci 3q21.31 (LZTFL1 and chemokine receptor genes) and 9q34.2 (ABO), associated with disease severity and susceptibility to infection, respectively, were the most replicated findings across studies. Genes involved with mucociliary clearance (CEP97, FOXP4), viral-entry (ACE2, SLC6A20) and mucosal immunity (MIR6891) are associated with the risk of SARS-CoV-2 infection while genes of antiviral immune response (IFNAR2, OAS1), leukocyte trafficking (CCR9, CXCR6) and lung injury (DPP9, NOTCH4) are associated with severe disease. The biological processes underlying the risk of infection occur prominently, but not exclusively, in the upper airways whereas the severe COVID-19-associated processes in alveolar-capillary interface. The COVID-19 GWASs has unraveled key genetic mechanisms of SARS-CoV-2 pathogenesis, although the genetic basis of other COVID-19 related phenotypes (long COVID and neurological impairment) remains to be elucidated.

The Third dose of CoronVac vaccination induces broad and potent adaptive immune responses that recognize SARS-CoV-2 Delta and Omicron variants

The waning humoral immunity and emerging contagious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants resulted in the necessity of the booster vaccination of coronavirus disease 2019 (COVID-19). The inactivated vaccine, CoronaVac, is the most widely supplied COVID-19 vaccine globally. Whether the CoronaVac booster elicited adaptive responses that cross-recognize SARS-CoV-2 variants of concern (VoCs) among 77 healthy subjects receiving the third dose of CoronaVac were explored. After the boost, remarkable elevated spike-specific IgG and IgA responses, as well as boosted neutralization activities, were observed, despite 3.0-fold and 5.9-fold reduced neutralization activities against Delta and Omicron strains compared to that of the ancestral strain. Furthermore, the booster dose induced potent B cells and memory B cells that cross-bound receptor-binding domain (RBD) proteins derived from VoCs, while Delta and Omicron RBD-specific memory B cell recognitions were reduced by 2.7-fold and 4.2-fold compared to that of ancestral strain, respectively. Consistently, spike-specific circulating follicular helper T cells (cTfh) significantly increased and remained stable after the boost, with a predominant expansion towards cTfh17 subpopulations. Moreover, SARS-CoV-2-specific CD4⁺ and CD8⁺ T cells peaked and sustained after the booster. Notably, CD4⁺ and CD8⁺ T cell recognition of VoC spike was largely preserved compared to the ancestral strain. Individuals without generating Delta or Omicron neutralization activities had comparable levels of CD4⁺ and CD8⁺ T cells responses as those with detectable neutralizing activities. Our study demonstrated that the CoronaVac booster induced broad and potent adaptive immune responses that could be effective in controlling SARS-CoV-2 Delta and Omicron variants.

Comparative global B cell receptor repertoire difference induced by SARS-CoV-2 infection or vaccination via single-cell V(D)J sequencing

Dynamic changes of the paired heavy and light chain B cell receptor (BCR) repertoire provide an essential insight into understanding the humoral immune response post-SARS-CoV-2 infection and vaccination. However, differences between the endogenous paired BCR repertoire kinetics in SARS-CoV-2 infection and previously recovered/naïve subjects treated with the inactivated vaccine remain largely unknown. We performed single-cell V(D)J sequencing of B cells from six healthy donors with three shots of inactivated SARS-CoV-2 vaccine (BBIBP-CorV), five people who received the BBIBP-CorV vaccine after having recovered from COVID-19, five unvaccinated COVID-19 recovered patients and then integrated with public data of B cells from four SARS-CoV-2-infected subjects. We discovered that BCR variable (V) genes were more prominently used in the SARS-CoV-2 exposed groups (both in the group with active infection and in the group that had recovered) than in the vaccinated groups. The VH gene that expanded the most after SARS-CoV-2 infection was IGHV3-33, while IGHV3-23 in the vaccinated groups. SARS-CoV-2-infected group enhanced more BCR clonal expansion and somatic hypermutation than the vaccinated healthy group. A small proportion of public clonotypes were shared between the SARS-CoV-2 infected, vaccinated healthy, and recovered groups. Moreover, several public antibodies had been identified against SARS-CoV-2 spike protein. We comprehensively characterize the paired heavy and light chain BCR repertoire from SARS-CoV-2 infection to vaccination, providing further guidance for the development of the next-generation precision vaccine.

A serological investigation in Southern Italy: was SARS-CoV-2 circulating in late 2019?

In March 2020, the first pandemic caused by a coronavirus was declared by the World Health Organization. Italy was one of the first and most severely affected countries, particularly the northern part of the country. The latest evidence suggests that the virus could have been circulating, at least in Italy, before the first autochthonous SARS-COV-2 case was detected in February 2020. The present study aimed to investigate the presence of antibodies against SARS-CoV-2 in human serum samples collected in the last months of 2019 (September–December) in the Apulia region, Southern Italy. Eight of 455 samples tested proved positive on in-house receptor-binding-domain-based ELISA. Given the month of collection of the positive samples, these findings may indicate early circulation of SARS-CoV-2 in Apulia region in the autumn of 2019. However, it cannot be completely ruled out that the observed sero-reactivity could be an unknown antigen specificity in another virus to which subjects were exposed containing an epitope adventitiously cross-reactive with an epitope of SARS-CoV-2.

SARS-CoV-2 Antibody Effectiveness Is Influenced by Non-Epitope Mutation/Binding-Induced Denaturation of the Epitope 3D Architecture

The public health threat from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to intensify with emerging variants of concern (VOC) aiming to render COVID-19 vaccines/infection-induced antibodies redundant. The SARS-CoV-2 spike protein is responsible for receptor binding and infection of host cells making it a legitimate antibody target. Antibodies mostly target epitopes in the receptor binding domain (RBD). Mutations occurring within epitopes influence antibody specificity and function by altering their 3D architecture. However, the mechanisms by which non-epitope mutations in the RBD influence antibody specificity and function remain a mystery. We used Protein Data Bank (PDB) deposited 3D structures for the original, Beta, Delta, BA.1, and BA.2 RBD proteins in complex with either neutralizing antibodies or Angiotensin-Converting Enzyme 2 (ACE2) to elucidate the structural and mechanistic basis for neutralizing antibody evasion driven by non-epitope amino acid substitutions in the RBD. Since the mechanism behind the extensively reported functional discrepancies between the same antibody when used individually and when used in an antibody cocktail is lacking, we explored the structural basis for this inconsistency. Finally, since SARS-CoV-2 antibodies are viral mutagens, we deciphered determinants for antibody-pressured amino acid substitutions. On the one hand, we show that non-epitope mutations in the RBD domain of SARS-CoV-2 VOC influence the formation of hydrogen bonds in the paratope-epitope interface by repositioning RBD amino-acid sidechains (AASCs). This increases the distance between complementary donor/acceptor atoms on paratope and epitope AASCs leading to weaker or the complete prevention of the formation of hydrogen bonds in the paratope-epitope interface. On the other hand, we show that SARS-CoV-2 VOC employ the same strategy to simultaneously search for complementary donor/acceptor atoms on ACE2 AASCs to form new interactions, potentially favoring increased viral transmission. Additionally, we illustrate that converting the spike protein to an RBD, a deletion mutation, also repositions epitope AASCs and that AASC interactions in the paratope-epitope interface vary when an antibody is used individually versus when utilized as a cocktail with other antibodies. Finally, we show that the process of substituting immunogenic RBD amino acids begins with the repositioning of their AASCs induced by immune/antibody pressure. We show that donor/acceptor atoms from any amino acid can determine cross-reactivity instead, provided they possess and present spatially pairing donor/acceptor atoms. By studying structural alignments for PDB deposited antibody-RBD 3D structures and relating them to published binding and neutralization profiles of the same antibodies, we demonstrate that minor structural alterations such as epitope AASC repositioning have a major impact on antibody effectiveness and, hence, should receive adequate attention given that protein structure dictates protein function.

An FcRn-targeted mucosal vaccine against SARS-CoV-2 infection and transmission

SARS-CoV-2 and its variants cause COVID-19, which is primarily transmitted through droplets and airborne aerosols. To prevent viral infection and reduce viral spread, vaccine strategies must elicit protective immunity in the airways. FcRn transfers IgG across epithelial barriers; we explore FcRn-mediated respiratory delivery of SARS-CoV-2 spike (S). A monomeric IgG Fc was fused to a stabilized S protein; the resulting S-Fc bound to S-specific antibodies (Ab) and FcRn. A significant increase in Ab responses was observed following the intranasal immunization of mice with S-Fc formulated in CpG as compared to the immunization with S alone or PBS. Furthermore, we intranasally immunize adult or aged mice and hamsters with S-Fc. A significant reduction of virus replication in nasal turbinate, lung, and brain was observed following nasal challenges with SARS-CoV-2, including Delta and Omicron variants. Intranasal immunization also significantly reduced viral transmission between immunized and naive hamsters. Protection was mediated by nasal IgA, serum-neutralizing Abs, tissue-resident memory T cells, and bone marrow S-specific plasma cells. Hence FcRn delivers an S-Fc antigen effectively into the airway and induces protection against SARS-CoV-2 infection and transmission. Based on these findings, FcRn-targeted non-invasive respiratory immunizations are superior strategies for preventing highly contagious respiratory viruses from spreading.

How Protective are Antibodies to SARS-CoV-2, the Main Weapon of the B-Cell Response?

Since the beginning of the Coronavirus disease (COVID)-19 pandemic in December 2019, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been responsible for more than 600 million infections and 6.5 million deaths worldwide. Given the persistence of SARS-CoV-2 and its ability to develop new variants, the implementation of an effective and long-term herd immunity appears to be crucial to overcome the pandemic. While a vast field of research has focused on the role of humoral immunity against SARS-CoV-2, a growing body of evidence suggest that antibodies alone only confer a partial protection against infection of reinfection which could be of high importance regarding the strategic development goals (SDG) of the United Nations (UN) and in particular UN SDG3 that aims towards the realization of good health and well being on a global scale in the context of the COVID-19 pandemic.In this review, we highlight the role of humoral immunity in the host defense against SARS-CoV-2, with a focus on highly neutralizing antibodies. We summarize the results of the main clinical trials leading to an overall disappointing efficacy of convalescent plasma therapy, variable results of monoclonal neutralizing antibodies in patients with COVID-19 but outstanding results for the mRNA based vaccines against SARS-CoV-2. Finally, we advocate that beyond antibody responses, the development of a robust cellular immunity against SARS-CoV-2 after infection or vaccination is of utmost importance for promoting immune memory and limiting disease severity, especially in case of (re)-infection by variant viruses.

Formulation, Device, and Clinical Factors Influencing the Targeted Delivery of COVID-19 Vaccines to the Lungs

The COVID-19 pandemic has proven to be an unprecedented health crisis in the human history with more than 5 million deaths worldwide caused to the SARS-CoV-2 and its variants ( https://www.who.int/emergencies/diseases/novel-coronavirus-2019 ). The currently authorized lipid nanoparticle (LNP)-encapsulated mRNA vaccines have been shown to have more than 90% vaccine efficacy at preventing COVID-19 illness (Baden et al. New England J Med 384(5):403-416, 2021; Thomas et al., 2021). In addition to vaccines, other small molecules belonging to the class of anti-viral and anti-inflammatory compounds have also been prescribed to reduce the viral proliferation and the associated cytokine storm. These anti-viral and anti-inflammatory compounds have also been shown to be effective in reducing COVID-19 exacerbations especially in reducing the host inflammatory response to SARS-CoV-2. However, all of the currently FDA-authorized vaccines for COVID-19 are meant for intramuscular injection directly into the systemic circulation. Also, most of the small molecules investigated for their anti-COVID-19 efficacy have also been explored using the intravenous route with a few of them explored for the inhalation route (Ramakrishnan et al. Lancet Respir Med 9:763-772, 2021; Horby et al. N Engl J Med 384(8):693-704, 2021). The fact that the SARS-CoV-2 enters the human body mainly via the nasal and airway route resulting in the lungs being the primary organs of infection as characterized by acute respiratory distress syndrome (ARDS)-mediated cytokine storm in the alveolar region has made the inhalation route gain significant attention for the purposes of targeting both vaccines and small molecules to the lungs (Mitchell et al., J Aerosol Med Pulm Drug Deliv 33(4):235-8, 2020). While there have been many studies reporting the safety and efficacy of targeting various therapeutics to the lungs to treat COVID-19, there is still a need to match the choice of inhalation formulation and the delivery device platform itself with the patient-related factors like breathing pattern and respiratory rate as seen in a clinical setting. In that perspective, this review aims to describe the various formulation and patient-related clinical factors that can play an important role in the judicious choice of the inhalation delivery platforms or devices for the development of inhaled COVID-19 vaccines.

Saliva and Plasma Neutralizing Activity Induced by the Administration of a Third bnt162b2 Vaccine Dose

The BNT162b2 vaccine induces neutralizing activity (NA) in serum, but no data are available on whether a third-dose activates specific-immunity within the oral mucosa, representing the primary route of viral-entry. To carefully address this issue, we investigated if such immunity is boosted by SARS-CoV-2-infection; how long it is maintained over-time; and if it protects against the SARS-CoV-2 lineage B.1 (EU) and the emerging Delta and Omicron variants. NA was measured in plasma and saliva samples from: uninfected SARS-CoV-2-Vaccinated (SV), subjects infected prior to vaccination (SIV), and subjects who were infected after the second (SIV2) or the third (SIV3) vaccine dose. Samples were collected immediately before (T0), 15 days (T1), and 90 days (T2) post third-dose administration (SV and SIV), or 15 days post-infection (SIV2 and SIV3). In all the enrolled groups, NA in plasma and saliva: (i) was higher against EU compared to the other variants at all time-points (SV: T0 and T1, EU vs. both Delta and Omicron p < 0.001; T2 p < 0.01) (SIV: T0, EU vs. Delta p < 0.05; EU vs. Omi p < 0.01; T1 and T2 EU vs. Delta p < 0.01; EU vs. Omi p < 0.001); (ii) was boosted by the administration of the third dose; iii) declined over-time, albeit being detectable in almost all subjects at T2. The monitoring of NA over time will be important in clarifying if different NA levels may influence either acquisition or course of infection to properly plan the timing of a fourth vaccine dose administration.

Targeting the Complement-Sphingolipid System in COVID-19 and Gaucher Diseases: Evidence for a New Treatment Strategy

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2)-induced disease (COVID-19) and Gaucher disease (GD) exhibit upregulation of complement 5a (C5a) and its C5aR1 receptor, and excess synthesis of glycosphingolipids that lead to increased infiltration and activation of innate and adaptive immune cells, resulting in massive generation of pro-inflammatory cytokines, chemokines and growth factors. This C5a-C5aR1-glycosphingolipid pathway- induced pro-inflammatory environment causes the tissue damage in COVID-19 and GD. Strikingly, pharmaceutically targeting the C5a-C5aR1 axis or the glycosphingolipid synthesis pathway led to a reduction in glycosphingolipid synthesis and innate and adaptive immune inflammation, and protection from the tissue destruction in both COVID-19 and GD. These results reveal a common involvement of the complement and glycosphingolipid systems driving immune inflammation and tissue damage in COVID-19 and GD, respectively. It is therefore expected that combined targeting of the complement and sphingolipid pathways could ameliorate the tissue destruction, organ failure, and death in patients at high-risk of developing severe cases of COVID-19.

Host Protective Immunity against Severe Acute Respiratory Coronavirus 2 (SARS-CoV-2) and the COVID-19 Vaccine-Induced Immunity against SARS-CoV-2 and Its Variants

The world is now apparently at the last/recovery stage of the COVID-19 pandemic, starting from 29 December 2019, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). With the progression of time, several mutations have taken place in the original SARS-CoV-2 Wuhan strain, which have generated variants of concern (VOC). Therefore, combatting COVID-19 has required the development of COVID-19 vaccines using several platforms. The immunity induced by those vaccines is vital to study in order to assure total protection against SARS-CoV-2 and its emerging variants. Indeed, understanding and identifying COVID-19 protection mechanisms or the host immune responses are of significance in terms of designing both new and repurposed drugs as well as the development of novel vaccines with few to no side effects. Detecting the immune mechanisms for host protection against SARS-CoV-2 and its variants is crucial for the development of novel COVID-19 vaccines as well as to monitor the effectiveness of the currently used vaccines worldwide. Immune memory in terms of the production of neutralizing antibodies (NAbs) during reinfection is also very crucial to formulate the vaccine administration schedule/vaccine doses. The response of antigen-specific antibodies and NAbs as well as T cell responses, along with the protective cytokine production and the innate immunity generated upon COVID-19 vaccination, are discussed in the current review in comparison to the features of naturally induced protective immunity.

Antibody tests for identification of current and past infection with SARS-CoV-2

BACKGROUND

The diagnostic challenges associated with the COVID-19 pandemic resulted in rapid development of diagnostic test methods for detecting SARS-CoV-2 infection. Serology tests to detect the presence of antibodies to SARS-CoV-2 enable detection of past infection and may detect cases of SARS-CoV-2 infection that were missed by earlier diagnostic tests. Understanding the diagnostic accuracy of serology tests for SARS-CoV-2 infection may enable development of effective diagnostic and management pathways, inform public health management decisions and understanding of SARS-CoV-2 epidemiology.

OBJECTIVES

To assess the accuracy of antibody tests, firstly, to determine if a person presenting in the community, or in primary or secondary care has current SARS-CoV-2 infection according to time after onset of infection and, secondly, to determine if a person has previously been infected with SARS-CoV-2. Sources of heterogeneity investigated included: timing of test, test method, SARS-CoV-2 antigen used, test brand, and reference standard for non-SARS-CoV-2 cases.

SEARCH METHODS

The COVID-19 Open Access Project living evidence database from the University of Bern (which includes daily updates from PubMed and Embase and preprints from medRxiv and bioRxiv) was searched on 30 September 2020. We included additional publications from the Evidence for Policy and Practice Information and Co-ordinating Centre (EPPI-Centre) 'COVID-19: Living map of the evidence' and the Norwegian Institute of Public Health 'NIPH systematic and living map on COVID-19 evidence'. We did not apply language restrictions.

SELECTION CRITERIA

We included test accuracy studies of any design that evaluated commercially produced serology tests, targeting IgG, IgM, IgA alone, or in combination. Studies must have provided data for sensitivity, that could be allocated to a predefined time period after onset of symptoms, or after a positive RT-PCR test. Small studies with fewer than 25 SARS-CoV-2 infection cases were excluded. We included any reference standard to define the presence or absence of SARS-CoV-2 (including reverse transcription polymerase chain reaction tests (RT-PCR), clinical diagnostic criteria, and pre-pandemic samples).

DATA COLLECTION AND ANALYSIS

We use standard screening procedures with three reviewers. Quality assessment (using the QUADAS-2 tool) and numeric study results were extracted independently by two people. Other study characteristics were extracted by one reviewer and checked by a second. We present sensitivity and specificity with 95% confidence intervals (CIs) for each test and, for meta-analysis, we fitted univariate random-effects logistic regression models for sensitivity by eligible time period and for specificity by reference standard group. Heterogeneity was investigated by including indicator variables in the random-effects logistic regression models. We tabulated results by test manufacturer and summarised results for tests that were evaluated in 200 or more samples and that met a modification of UK Medicines and Healthcare products Regulatory Agency (MHRA) target performance criteria.

MAIN RESULTS

We included 178 separate studies (described in 177 study reports, with 45 as pre-prints) providing 527 test evaluations. The studies included 64,688 samples including 25,724 from people with confirmed SARS-CoV-2; most compared the accuracy of two or more assays (102/178, 57%). Participants with confirmed SARS-CoV-2 infection were most commonly hospital inpatients (78/178, 44%), and pre-pandemic samples were used by 45% (81/178) to estimate specificity. Over two-thirds of studies recruited participants based on known SARS-CoV-2 infection status (123/178, 69%). All studies were conducted prior to the introduction of SARS-CoV-2 vaccines and present data for naturally acquired antibody responses. Seventy-nine percent (141/178) of studies reported sensitivity by week after symptom onset and 66% (117/178) for convalescent phase infection. Studies evaluated enzyme-linked immunosorbent assays (ELISA) (165/527; 31%), chemiluminescent assays (CLIA) (167/527; 32%) or lateral flow assays (LFA) (188/527; 36%). Risk of bias was high because of participant selection (172, 97%); application and interpretation of the index test (35, 20%); weaknesses in the reference standard (38, 21%); and issues related to participant flow and timing (148, 82%). We judged that there were high concerns about the applicability of the evidence related to participants in 170 (96%) studies, and about the applicability of the reference standard in 162 (91%) studies. Average sensitivities for current SARS-CoV-2 infection increased by week after onset for all target antibodies. Average sensitivity for the combination of either IgG or IgM was 41.1% in week one (95% CI 38.1 to 44.2; 103 evaluations; 3881 samples, 1593 cases), 74.9% in week two (95% CI 72.4 to 77.3; 96 evaluations, 3948 samples, 2904 cases) and 88.0% by week three after onset of symptoms (95% CI 86.3 to 89.5; 103 evaluations, 2929 samples, 2571 cases). Average sensitivity during the convalescent phase of infection (up to a maximum of 100 days since onset of symptoms, where reported) was 89.8% for IgG (95% CI 88.5 to 90.9; 253 evaluations, 16,846 samples, 14,183 cases), 92.9% for IgG or IgM combined (95% CI 91.0 to 94.4; 108 evaluations, 3571 samples, 3206 cases) and 94.3% for total antibodies (95% CI 92.8 to 95.5; 58 evaluations, 7063 samples, 6652 cases). Average sensitivities for IgM alone followed a similar pattern but were of a lower test accuracy in every time slot. Average specificities were consistently high and precise, particularly for pre-pandemic samples which provide the least biased estimates of specificity (ranging from 98.6% for IgM to 99.8% for total antibodies). Subgroup analyses suggested small differences in sensitivity and specificity by test technology however heterogeneity in study results, timing of sample collection, and smaller sample numbers in some groups made comparisons difficult. For IgG, CLIAs were the most sensitive (convalescent-phase infection) and specific (pre-pandemic samples) compared to both ELISAs and LFAs (P < 0.001 for differences across test methods). The antigen(s) used (whether from the Spike-protein or nucleocapsid) appeared to have some effect on average sensitivity in the first weeks after onset but there was no clear evidence of an effect during convalescent-phase infection. Investigations of test performance by brand showed considerable variation in sensitivity between tests, and in results between studies evaluating the same test. For tests that were evaluated in 200 or more samples, the lower bound of the 95% CI for sensitivity was 90% or more for only a small number of tests (IgG, n = 5; IgG or IgM, n = 1; total antibodies, n = 4). More test brands met the MHRA minimum criteria for specificity of 98% or above (IgG, n = 16; IgG or IgM, n = 5; total antibodies, n = 7). Seven assays met the specified criteria for both sensitivity and specificity. In a low-prevalence (2%) setting, where antibody testing is used to diagnose COVID-19 in people with symptoms but who have had a negative PCR test, we would anticipate that 1 (1 to 2) case would be missed and 8 (5 to 15) would be falsely positive in 1000 people undergoing IgG or IgM testing in week three after onset of SARS-CoV-2 infection. In a seroprevalence survey, where prevalence of prior infection is 50%, we would anticipate that 51 (46 to 58) cases would be missed and 6 (5 to 7) would be falsely positive in 1000 people having IgG tests during the convalescent phase (21 to 100 days post-symptom onset or post-positive PCR) of SARS-CoV-2 infection.

AUTHORS' CONCLUSIONS

Some antibody tests could be a useful diagnostic tool for those in whom molecular- or antigen-based tests have failed to detect the SARS-CoV-2 virus, including in those with ongoing symptoms of acute infection (from week three onwards) or those presenting with post-acute sequelae of COVID-19. However, antibody tests have an increasing likelihood of detecting an immune response to infection as time since onset of infection progresses and have demonstrated adequate performance for detection of prior infection for sero-epidemiological purposes. The applicability of results for detection of vaccination-induced antibodies is uncertain.

An intranasal vaccine targeting the receptor binding domain of SARS-CoV-2 elicits a protective immune response

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the pathogen responsible for COVID-19, has caused an ongoing worldwide pandemic. Due to the rapid emergence of variants of concern (VOCs), novel vaccines and vaccination strategies are urgently needed. We developed an intranasal vaccine consisting of the SARS-CoV-2 receptor binding domain (RBD) fused to the antibody Fc fragment (RBD-Fc). RBD-Fc could induce strong humoral immune responses via intranasal vaccination. Notably, this immunogen could efficiently induce IgG and IgA and establish mucosal immunity in the respiratory tract. The induced antibodies could efficiently neutralize wild-type SARS-CoV-2 and currently identified SARS-CoV-2 VOCs, including the Omicron variant. In a mouse model, intranasal immunization could provide complete protection against a lethal SARS-CoV-2 challenge. Unfortunately, the limitation of our study is the small number of animals used in the immune response analysis. Our results suggest that recombinant RBD-Fc delivered via intranasal vaccination has considerable potential as a mucosal vaccine that may reduce the risk of SARS-CoV-2 infection.

Genetic regulation of serum IgA levels and susceptibility to common immune, infectious, kidney, and cardio-metabolic traits

Immunoglobulin A (IgA) mediates mucosal responses to food antigens and the intestinal microbiome and is involved in susceptibility to mucosal pathogens, celiac disease, inflammatory bowel disease, and IgA nephropathy. We performed a genome-wide association study of serum IgA levels in 41,263 individuals of diverse ancestries and identified 20 genome-wide significant loci, including 9 known and 11 novel loci. Co-localization analyses with expression QTLs prioritized candidate genes for 14 of 20 significant loci. Most loci encoded genes that produced immune defects and IgA abnormalities when genetically manipulated in mice. We also observed positive genetic correlations of serum IgA levels with IgA nephropathy, type 2 diabetes, and body mass index, and negative correlations with celiac disease, inflammatory bowel disease, and several infections. Mendelian randomization supported elevated serum IgA as a causal factor in IgA nephropathy. African ancestry was consistently associated with higher serum IgA levels and greater frequency of IgA-increasing alleles compared to other ancestries. Our findings provide novel insights into the genetic regulation of IgA levels and its potential role in human disease.

Longitudinal Antibody Titer, Avidity, and Neutralizing Responses after SARS-CoV-2 Infection

While waning immunity and SARS-CoV-2 variant immune escape continue to result in high infection rates worldwide, associations between longitudinal quantitative, qualitative, and functional humoral immune responses after SARS-CoV-2 infection remain unclear. In this study, we found significant waning of antibody against Spike S1 (R = −0.32, p = 0.035) and N protein (R = −0.39, p = 0.008), while RBD antibody moderately decreased (R = −0.19, p = 0.203). Likewise, neutralizing antibody titer (ND₅₀) waned over time (R = −0.46, p = 0.001). In contrast, antibody avidity increased significantly over time for Spike S1 (R = 0.62, p = 6.0e−06), RBD (R = 0.54, p = 2.0e−04), and N (R = 0.33, p = 0.025) antibodies. Across all humoral responses, ND₅₀ strongly associated with Spike S1 (R = 0.85, p = 2.7e−13) and RBD (R = 0.78, p = 2.9e−10) antibodies. Our findings provide longitudinal insight into humoral immune responses after infection and imply the potential of Spike S1/RBD antibody titer as surrogate correlates of protection.

Antibody response after COVID-19 vaccination in intravenous immunoglobulin-treated immune neuropathies

BACKGROUND AND PURPOSE

This study assessed the prevalence of anti-SARS-CoV-2 antibodies in therapeutic immunoglobulin and their impact on serological response to COVID-19 mRNA vaccine in patients with intravenous immunoglobulin (IVIg)-treated chronic immune neuropathies.

METHODS

Forty-six samples of different brands or lots of IVIg or subcutaneous IgG were analyzed for anti-SARS-CoV-2 IgG using enzyme-linked immunosorbent assay and chemiluminescent microparticle immunoassay. Blood sera from 16 patients with immune neuropathies were prospectively analyzed for anti-SARS-CoV-2 IgA, IgG, and IgM before and 1 week after IVIg infusion subsequent to consecutive COVID-19 mRNA vaccine doses and after 12 weeks. These were compared to 42 healthy subjects.

RESULTS

Twenty-four (52%) therapeutic immunoglobulin samples contained anti-SARS-CoV-2 IgG. All patients with immune neuropathies (mean age = 65 ± 16 years, 25% female) were positive for anti-SARS-CoV-2 IgG after COVID-19 vaccination. Anti-SARS-CoV-2 IgA titers significantly decreased 12-14 weeks after vaccination (p = 0.02), whereas IgG titers remained stable (p = 0.2). IVIg did not significantly reduce intraindividual anti-SARS-CoV-2 IgA/IgG serum titers in immune neuropathies (p = 0.69). IVIg-derived anti-SARS-CoV-2 IgG did not alter serum anti-SARS-CoV-2 IgG decrease after IVIg administration (p = 0.67).

CONCLUSIONS

Our study indicates that IVIg does not impair the antibody response to COVID-19 mRNA vaccine in a short-term observation, when administered a minimum of 2 weeks after each vaccine dose. The infusion of current IVIg preparations that contain anti-SARS-CoV-2 IgG does not significantly alter serum anti-SARS-CoV-2 IgG titers.

Role of the humoral immune response during COVID-19: guilty or not guilty?

Systemic and mucosal humoral immune responses are crucial to fight respiratory viral infections in the current pandemic of COVID-19 caused by the SARS-CoV-2 virus. During SARS-CoV-2 infection, the dynamics of systemic and mucosal antibody infections are affected by patient characteristics, such as age, sex, disease severity, or prior immunity to other human coronaviruses. Patients suffering from severe disease develop higher levels of anti-SARS-CoV-2 antibodies in serum and mucosal tissues than those with mild disease, and these antibodies are detectable for up to a year after symptom onset. In hospitalized patients, the aberrant glycosylation of anti-SARS-CoV-2 antibodies enhances inflammation-associated antibody Fc-dependent effector functions, thereby contributing to COVID-19 pathophysiology. Current vaccines elicit robust humoral immune responses, principally in the blood. However, they are less effective against new viral variants, such as Delta and Omicron. This review provides an overview of current knowledge about the humoral immune response to SARS-CoV-2, with a particular focus on the protective and pathological role of humoral immunity in COVID-19 severity. We also discuss the humoral immune response elicited by COVID-19 vaccination and protection against emerging viral variants.

IgA quantification as a good predictor of the neutralizing antibodies levels after vaccination against SARS-CoV-2

Background

Vaccination against COVID-19 was implemented very quickly, but the emergence of new variants that can evade the previous acquired immunological protection highlights the importance of understanding the mechanisms involved in the immune response generated after SARS-CoV-2 infection or vaccination.

Objectives

Since most of our knowledge on the humoral immunity generated against SARS-CoV-2 has been obtained from studies with infected patients before vaccination, our goal here was to evaluate seroconversion and its correlation with the titers of neutralizing antibodies (NAbs) in individuals who received the complete initial recommended vaccination schedule with three different vaccines.

Study design

We analyzed serum IgG, IgA and total NAbs against the trimeric SARS-CoV-2 Spike (S) protein or its receptor binding domain (RBD) in blood samples collected from 118 healthy individuals without known previous infection, before and after receiving the first and the second dose of CoronaVac (n = 18), ChAdOx-1 (n = 68) or BNT162b2 (n = 32) vaccines.

Results

We found that although IgG titers were high in all sera collected after the two doses of these vaccines, NAbs amounts varies among the groups. In contrast, serum NAbs concentrations were much more comparable to the IgA levels, indicating that these antibodies would have a major neutralizing capacity against SARS-CoV-2.

Conclusions

Altogether our data suggest that quantification of serum anti-S or anti-RBD IgA, rather than IgG, may be a valuable tool to screen NAbs and may be considered for surveillance of vaccine coverage.

Anti-Saccharomyces cerevisiae antibodies in patients with COVID-19

BACKGROUND AND STUDY AIM

Anti-Saccharomyces cerevisiae antibodies (ASCA) have been described in many autoimmune diseases (AIDs). Coronavirus disease 2019 (COVID-19) could trigger AIDs. This study aimed to determine the frequency of ASCA in patients with COVID-19.

PATIENTS AND METHODS

This study included 88 adult patients with severe COVID-19, 51 mild COVID-19, and 160 healthy blood donors. ASCA of isotype immunoglobulin (Ig)G and IgA were detected by enzyme-linked immunosorbent assay.

RESULTS

The frequency of ASCA (IgG or IgA) was significantly higher in patients with severe COVID-19 (21.6 % vs 3.7 %, p < 10^-3) and in patients with mild COVID-19 than in the healthy controls (13.7 % vs 3.7 %, p = 0.03). ASCA-IgA was significantly more frequent in patients with severe COVID-19 than in healthy controls (15.9 % vs 0.6 %, p < 10^-3). ASCA-IgG was significantly more frequent in patients with mild COVID-19 than in healthy controls (13.7 % vs 3.1 %, p = 0.02). ASCA (IgG or IgA) were more frequent in severe than in mild COVID-19, but the difference was not statistically significant (21.6 % vs 13.7 %). ASCA-IgA was significantly more frequent in patients with severe than those with mild COVID-19 (15.9 % vs 0 %, p = 0.003). The mean ASCA-IgG and ASCA-IgA levels were significantly higher in patients with severe COVID-19 than in healthy controls (5.8 U/mL ± 11.8 vs 2.3 U/mL ± 2.8, p < 10^-3 and 9.2 U/mL ± 21.5 vs 3.4 U/mL ± 1.7, respectively, p < 10^-3). The mean ASCA-IgG levels were significantly higher in patients with mild COVID-19 than in healthy controls (6.2 U/mL ± 12.9 vs 2.3 U/mL ± 2.8, p < 10^-3). The mean ASCA-IgA levels were significantly higher in patients with severe than in those with mild COVID-19 (9.2 U/mL ± 21.5 vs 2.6 U/mL ± 1.2, p = 0.03).

CONCLUSION

ASCA was more frequent in patients with COVID-19 than in healthy controls.

Infection of the oral cavity with SARS-CoV-2 variants: Scope of salivary diagnostics

Coronaviruses, including SARS-CoV-2, have caused pandemics in the past two decades. The most prevalent SARS-CoV-2 variants of concern can re-infect individuals who have been previously infected with other variants or had protection from vaccines targeting the original SARS-CoV-2 variant. Given the high risk of transmission of coronavirus via aerosols produced during dental procedures, it is important to understand the future risk of coronavirus infection for oral health professionals and to diagnose quickly early stages of outbreaks. Testing of saliva for coronavirus may be the least invasive and most convenient method for following the outbreak at the individual and community level. This review will describe strategies for diagnosis of coronavirus in saliva.

Longitudinal serologic and viral testing post-SARS-CoV-2 infection and post-receipt of mRNA COVID-19 vaccine in a nursing home cohort-Georgia, October 2020‒April 2021

There are limited data describing SARS-CoV-2-specific immune responses and their durability following infection and vaccination in nursing home residents. We conducted a prospective longitudinal evaluation of 11 consenting SARS-CoV-2-positive nursing home residents to evaluate the quantitative titers and durability of binding antibodies detected after SARS-CoV-2 infection and subsequent COVID-19 vaccination. The evaluation included nine visits over 150 days from October 25, 2020, through April 1, 2021. Visits included questionnaire administration, blood collection for serology, and paired anterior nasal specimen collection for testing by BinaxNOW™ COVID-19 Ag Card (BinaxNOW), reverse transcription polymerase chain reaction (RT-PCR), and viral culture. We evaluated quantitative titers of binding SARS-CoV-2 antibodies post-infection and post-vaccination (beginning after the first dose of the primary series). The median age among participants was 74 years; one participant was immunocompromised. Of 10 participants with post-infection serology results, 9 (90%) had detectable Pan-Ig, IgG, and IgA antibodies, and 8 (80%) had detectable IgM antibodies. At first antibody detection post-infection, two-thirds (6/9, 67%) of participants were RT-PCR-positive, but none were culture- positive. Ten participants received vaccination; all had detectable Pan-Ig, IgG, and IgA antibodies through their final observation ≤90 days post-first dose. Post-vaccination geometric means of IgG titers were 10-200-fold higher than post-infection. Nursing home residents in this cohort mounted robust immune responses to SARS-CoV-2 post-infection and post-vaccination. The augmented antibody responses post-vaccination are potential indicators of enhanced protection that vaccination may confer on previously infected nursing home residents.

SARS-CoV-2-The Role of Natural Immunity: A Narrative Review

BACKGROUND

Both natural immunity and vaccine-induced immunity to COVID-19 may be useful to reduce the mortality/morbidity of this disease, but still a lot of controversy exists.

AIMS

This narrative review analyzes the literature regarding these two immunitary processes and more specifically: (a) the duration of natural immunity; (b) cellular immunity; (c) cross-reactivity; (d) the duration of post-vaccination immune protection; (e) the probability of reinfection and its clinical manifestations in the recovered patients; (f) the comparisons between vaccinated and unvaccinated as to the possible reinfections; (g) the role of hybrid immunity; (h) the effectiveness of natural and vaccine-induced immunity against Omicron variant; (i) the comparative incidence of adverse effects after vaccination in recovered individuals vs. COVID-19-naïve subjects.

MATERIAL AND METHODS

through multiple search engines we investigated COVID-19 literature related to the aims of the review, published since April 2020 through July 2022, including also the previous articles pertinent to the investigated topics.

RESULTS

nearly 900 studies were collected, and 246 pertinent articles were included. It was highlighted that the vast majority of the individuals after suffering from COVID-19 develop a natural immunity both of cell-mediated and humoral type, which is effective over time and provides protection against both reinfection and serious illness. Vaccine-induced immunity was shown to decay faster than natural immunity. In general, the severity of the symptoms of reinfection is significantly lower than in the primary infection, with a lower degree of hospitalizations (0.06%) and an extremely low mortality.

CONCLUSIONS

this extensive narrative review regarding a vast number of articles highlighted the valuable protection induced by the natural immunity after COVID-19, which seems comparable or superior to the one induced by anti-SARS-CoV-2 vaccination. Consequently, vaccination of the unvaccinated COVID-19-recovered subjects may not be indicated. Further research is needed in order to: (a) measure the durability of immunity over time; (b) evaluate both the impacts of Omicron BA.5 on vaccinated and healed subjects and the role of hybrid immunity.

Heterologous SARS-CoV-2 IgA neutralising antibody responses in convalescent plasma

OBJECTIVES

Following infection with SARS-CoV-2, virus-specific antibodies are generated, which can both neutralise virions and clear infection via Fc effector functions. The importance of IgG antibodies for protection and control of SARS-CoV-2 has been extensively reported. By comparison, other antibody isotypes including IgA have been poorly characterised.

METHODS

Here, we characterised plasma IgA from 41 early convalescent COVID-19 subjects for neutralisation and Fc effector functions.

RESULTS

Convalescent plasma IgA from > 60% of the cohort had the capacity to inhibit the interaction between wild-type RBD and ACE2. Furthermore, a third of the cohort induced stronger IgA-mediated ACE2 inhibition than matched IgG when tested at equivalent concentrations. Plasma IgA and IgG from this cohort broadly recognised similar RBD epitopes and had similar capacities to inhibit ACE2 from binding to 22 of the 23 prevalent RBD mutations assessed. However, plasma IgA was largely incapable of mediating antibody-dependent phagocytosis in comparison with plasma IgG.

CONCLUSION

Overall, convalescent plasma IgA contributed to the neutralising antibody response of wild-type SARS-CoV-2 RBD and various RBD mutations. However, this response displayed large heterogeneity and was less potent than IgG.

Harnessing Nasal Immunity with IgA to Prevent Respiratory Infections

The nasal cavity is a primary checkpoint for the invasion of respiratory pathogens. Numerous pathogens, including SARS-CoV-2, S. pneumoniae, S. aureus, etc., can adhere/colonize nasal lining to trigger an infection. Secretory IgA (sIgA) serves as the first line of immune defense against foreign pathogens. sIgA facilitates clearance of pathogenic microbes by intercepting their access to epithelial receptors and mucus entrapment through immune exclusion. Elevated levels of neutralizing IgA at the mucosal surfaces are associated with a high level of protection following intranasal immunizations. This review summarizes recent advances in intranasal vaccination technology and challenges in maintaining nominal IgA levels at the mucosal surface. Overall, the review emphasizes the significance of IgA-mediated nasal immunity, which holds a tremendous potential to mount protection against respiratory pathogens.

Sustained seropositivity up to 20.5 months after COVID-19

This study evaluated the persistence of IgM, IgA, and IgG to SARS-CoV-2 spike and nucleocapsid antigens up to 616 days since the onset of symptoms in a longitudinal cohort of 247 primary health care workers from Barcelona, Spain, followed up since the start of the pandemic. The study also assesses factors affecting antibody levels, including comorbidities and the responses to variants of concern as well as the frequency of reinfections. Despite a gradual and significant decline in antibody levels with time, seropositivity to five SARS-CoV-2 antigens combined was always higher than 90% over the whole study period. In a subset of 23 participants who had not yet been vaccinated by November 2021, seropositivity remained at 95.65% (47.83% IgM, 95.65% IgA, 95.65% IgG). IgG seropositivity against Alpha and Delta predominant variants was comparable to that against the Wuhan variant, while it was lower for Gamma and Beta (minority) variants and for IgA and IgM. Antibody levels at the time point closest to infection were associated with age, smoking, obesity, hospitalization, fever, anosmia/hypogeusia, chest pain, and hypertension in multivariable regression models. Up to 1 year later, just before the massive roll out of vaccination, antibody levels were associated with age, occupation, hospitalization, duration of symptoms, anosmia/hypogeusia, fever, and headache. In addition, tachycardia and cutaneous symptoms associated with slower antibody decay, and oxygen supply with faster antibody decay. Eight reinfections (3.23%) were detected in low responders, which is consistent with a sustained protective role for anti-spike naturally acquired antibodies. Stable persistence of IgG and IgA responses and cross-recognition of the predominant variants circulating in the 2020-2021 period indicate long-lasting and largely variant-transcending humoral immunity in the initial 20.5 months of the pandemic, in the absence of vaccination.

COVID-19 in Pregnant Women, Maternal-Fetal Involvement, and Vertical Mother-to-Child Transmission: A Systematic Review

Pregnant women are included in the COVID-19 risk groups even if they do not have any pathology. This requires an analysis of research focused on pregnant women to understand the impact of SARS-CoV-2 on their condition. There is also a need to know whether there is vertical mother-to-child transmission, as well as other consequences in case the pregnant woman is infected and COVID-19 positive. A systematic review was carried out to analyze the existing information on the complications of a pregnant woman infected with the SARS-CoV-2 coronavirus and the possibility of vertical transmission from mother to child, registered in the PROSPERO website and searched in the PubMed, Scopus, CINAHL, and Cochrane Library databases. Finally, 22 articles were included in the review. The review suggests that vertical transmission from mother to child could be exceptionally possible at the time of delivery or breastfeeding, but not through the placenta. It is interesting to point out the good acceptance of vaccination by pregnant women, which may be the reason for the low infectivity. Further research on pregnant women should be carried out to provide evidence on vertical mother-to-child transmission and the role of breast milk in relation to SARS-CoV-2.

SARS-CoV-2 specific antibody trajectories in mothers and infants over two months following maternal infection

Infants exposed to caregivers infected with SARS-CoV-2 may have heightened infection risks relative to older children due to their more intensive care and feeding needs. However, there has been limited research on COVID-19 outcomes in exposed infants beyond the neonatal period. Between June 2020 - March 2021, we conducted interviews and collected capillary dried blood spots from 46 SARS-CoV-2 infected mothers and their infants (aged 1-36 months) for up to two months following maternal infection onset (COVID+ group, 87% breastfeeding). Comparative data were also collected from 26 breastfeeding mothers with no known SARS-CoV-2 infection or exposures (breastfeeding control group), and 11 mothers who tested SARS-CoV-2 negative after experiencing symptoms or close contact exposure (COVID- group, 73% breastfeeding). Dried blood spots were assayed for anti-SARS-CoV-2 S-RBD IgG and IgA positivity and anti-SARS-CoV-2 S1 + S2 IgG concentrations. Within the COVID+ group, the mean probability of seropositivity among infant samples was lower than that of corresponding maternal samples (0.54 and 0.87, respectively, for IgG; 0.33 and 0.85, respectively, for IgA), with likelihood of infant infection positively associated with the number of maternal symptoms and other household infections reported. COVID+ mothers reported a lower incidence of COVID-19 symptoms among their infants as compared to themselves and other household adults, and infants had similar PCR positivity rates as other household children. No samples returned by COVID- mothers or their infants tested antibody positive. Among the breastfeeding control group, 44% of mothers but none of their infants tested antibody positive in at least one sample. Results support previous research demonstrating minimal risks to infants following maternal COVID-19 infection, including for breastfeeding infants.

Adaptive immunity to SARS-CoV-2 infection: A systematic review

Background

There is evidence that the adaptive or acquired immune system is one of the crucial variables in differentiating the course of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This work aimed to analyze the immunopathological aspects of adaptive immunity that are involved in the progression of this disease.

Methods

This is a systematic review based on articles that included experimental evidence from in vitro assays, cohort studies, reviews, cross-sectional and case-control studies from PubMed, SciELO, MEDLINE, and Lilacs databases in English, Portuguese, or Spanish between January 2020 and July 2022.

Results

Fifty-six articles were finalized for this review. CD4+ T cells were the most resolutive in the health-disease process compared with B cells and CD8+ T lymphocytes. The predominant subpopulations of T helper lymphocytes (Th) in critically ill patients are Th1, Th2, Th17 (without their main characteristics) and regulatory T cells (Treg), while in mild cases there is an influx of Th1, Th2, Th17 and follicular T helper cells (Tfh). These cells are responsible for the secretion of cytokines, including interleukin (IL) - 6, IL-4, IL-10, IL-7, IL-22, IL-21, IL-15, IL-1α, IL-23, IL-5, IL-13, IL-2, IL-17, tumor necrosis factor alpha (TNF-α), CXC motivating ligand (CXCL) 8, CXCL9 and tumor growth factor beta (TGF-β), with the abovementioned first 8 inflammatory mediators related to clinical benefits, while the others to a poor prognosis. Some CD8+ T lymphocyte markers are associated with the severity of the disease, such as human leukocyte antigen (HLA-DR) and programmed cell death protein 1 (PD-1). Among the antibodies produced by SARS-CoV-2, Immunoglobulin (Ig) A stood out due to its potent release associated with a more severe clinical form.

Conclusions

It is concluded that through this study it is possible to have a brief overview of the main immunological biomarkers and their function during SARS-CoV-2 infection in particular cell types. In critically ill individuals, adaptive immunity is varied, aberrantly compromised, and late. In particular, the T-cell response is also an essential and necessary component in immunological memory and therefore should be addressed in vaccine formulation strategies.

Tolerability and immunogenicity of an intranasally-administered adenovirus-vectored COVID-19 vaccine: An open-label partially-randomised ascending dose phase I trial

BACKGROUND

Intranasal vaccination may induce protective local and systemic immune responses against respiratory pathogens. A number of intranasal SARS-CoV-2 vaccine candidates have achieved protection in pre-clinical challenge models, including ChAdOx1 nCoV-19 (AZD1222, University of Oxford / AstraZeneca).

METHODS

We performed a single-centre open-label Phase I clinical trial of intranasal vaccination with ChAdOx1 nCoV-19 in healthy adults, using the existing formulation produced for intramuscular administration. Thirty SARS-CoV-2 vaccine-naïve participants were allocated to receive 5 × 10⁹ viral particles (VP, n=6), 2 × 10¹⁰ VP (n=12), or 5 × 10¹⁰ VP (n=12). Fourteen received second intranasal doses 28 days later. A further 12 received non-study intramuscular mRNA SARS-CoV-2 vaccination between study days 22 and 46. To investigate intranasal ChAdOx1 nCoV-19 as a booster, six participants who had previously received two intramuscular doses of ChAdOx1 nCoV-19 and six who had received two intramuscular doses of BNT162b2 (Pfizer / BioNTech) were given a single intranasal dose of 5 × 10¹⁰ VP of ChAdOx1 nCoV-19. Objectives were to assess safety (primary) and mucosal antibody responses (secondary).

FINDINGS

Reactogenicity was mild or moderate. Antigen-specific mucosal antibody responses to intranasal vaccination were detectable in a minority of participants, rarely exceeding levels seen after SARS-CoV-2 infection. Systemic responses to intranasal vaccination were typically weaker than after intramuscular vaccination with ChAdOx1 nCoV-19. Antigen-specific mucosal antibody was detectable in participants who received an intramuscular mRNA vaccine after intranasal vaccination. Seven participants developed symptomatic SARS-CoV-2 infection.

INTERPRETATION

This formulation of intranasal ChAdOx1 nCoV-19 showed an acceptable tolerability profile but induced neither a consistent mucosal antibody response nor a strong systemic response.

FUNDING

AstraZeneca.