SARS CoV-2 Delta variant exhibits enhanced infectivity and a minor decrease in neutralization sensitivity to convalescent or post-vaccination sera

Rapid isolation of pan-neutralizing antibodies against Omicron variants from convalescent individuals infected with SARS-CoV-2

Introduction

The emergence of SARS-CoV-2 Omicron subvariants has presented a significant challenge to global health, as these variants show resistance to most antibodies developed early in the pandemic. Therapeutic antibodies with potent efficacy to the Omicron variants are urgently demanded.

Methods

Utilizing the rapid antibody discovery platform, Berkeley Lights Beacon, we isolated two monoclonal neutralizing antibodies, 2173-A6 and 3462-A4. These antibodies were isolated from individuals who recently recovered from Omicron infections.

Results

Both antibodies, 2173-A6 and 3462-A4, demonstrated high affinity for the RBD and effectively neutralized pseudoviruses from various Omicron lineages, including BA.4/5, XBB.1.16, XBB.1.5, and EG.5.1. This neutralization was achieved through binding to identical or overlapping epitopes.

Discussion

The use of the Beacon platform enabled the rapid isolation and identification of effective neutralizing antibodies within less than 10 days. This process significantly accelerates the development of novel therapeutic antibodies, potentially reducing the time required to respond to unknown infectious diseases in the future.

Therapeutic antibodies and alternative formats against SARS-CoV-2

The COVID-19 pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) heavily burdened the entire world. Despite a prompt generation of vaccines and therapeutics to confront infection, the virus remains a threat. The ancestor viral strain has evolved into several variants of concern, with the Omicron variant now having many distinct sublineages. Consequently, most available antibodies targeting the spike went obsolete and thus new therapies or therapeutic formats are needed. In this review we focus on antibody targets, provide an overview of the therapeutic progress made so far, describe novel formats being explored, and lessons learned from therapeutic antibodies that can enhance pandemic preparedness.

Differential platelet activation through an interaction with spike proteins of different SARS-CoV-2 variants

COVID-19 disease is associated with an increased risk of thrombotic complications, which contribute to high short-term mortality. Patients with COVID-19 demonstrate enhanced platelet turnover and reactivity, which may have a role in the development of thrombotic events and disease severity. Evidence has suggested direct interaction between SARS-CoV-2 and platelets, resulting in platelets activation. Here, we compare the effect of various SARS-CoV-2 spike variants on platelet activation. Engineered lentiviral particles were pseudotyped with spike SARS-CoV-2 variants and incubated with Platelet Rich Plasma obtained from healthy individuals. The pseudotyped SARS-CoV-2 exhibiting the wild-type Wuhan-Hu spike protein stimulated platelets to increase expression of the surface CD62P and activated αIIbβ3 markers by 3.5 ± 1.2 and 3.3 ± 0.7 fold, respectively (P = 0.004 and 0.003). The Delta variant induced much higher levels of platelet activation; CD62P expression was increased by 6.6 ± 2.2 fold and activated αIIbβ3 expression was increased by 5.0 ± 1.5 fold (P = 0.005 and 0.026, respectively). The Omicron BA.1 and the Alpha variants induced the lowest level of activation; CD62P expression was increased by 1.7 ± 0.4 and 1.6 ± 0.9 fold, respectively (P = 0.003 and 0.008), and activated αIIbβ3 expression by 1.8 ± 1.1 and 1.6 ± 0.8, respectively (P = 0.003 and 0.001). The Omicron BA.2 variant induced an increase of platelets activation comparable to the Wuhan-Hu (2.8 ± 1.2 and 2.1 ± 1.3 fold for CD62P and activated αIIbβ3 markers, respectively). The results obtained for various COVID-19 variants are in correlation with the clinical severity and mortality reported for these variants.

Comparative Study of the Mutations Observed in the SARS-CoV-2 RBD Variants of Concern and Their Impact on the Interaction with the ACE2 Protein

SARS-CoV-2 strains have made an appearance across the globe, causing over 757 million cases and over 6.85 million deaths at the time of writing. The emergence of these variants shows the amplitude of genetic variation to which the wild-type strains have been subjected. The rise of the different SARS-CoV-2 variants resulting from such genetic modification has significantly affected COVD-19's major impact on proliferation, virulence, and clinics. With the emergence of the variants of concern, the spike protein has been identified as a possible therapeutic target due to its critical role in binding to human cells and pathogenesis. These mutations could be linked to functional heterogeneity and use a different infection strategy. For example, the Omicron variant's multiple mutations should be carefully examined, as they represent one of the most widely spread strains and hint to us that there may be more genetic changes in the virus. As a result, we applied a common protocol where we reconstructed SARS-CoV-2 variants of concern and performed molecular dynamics simulations to study the stability of the ACE2-RBD complex in each variant. We also carried out free energy calculations to compare the binding and biophysical properties of the different SARS-CoV-2 variants when they interact with ACE2. Therefore, we were able to obtain consistent results and uncover new crucial residues that were essential for preserving a balance between maintaining a high affinity for ACE2 and the capacity to evade RBD-targeted antibodies. Our detailed structural analysis showed that SARS-CoV-2 variants of concern show a higher affinity for ACE2 compared to the Wuhan strain. Additionally, residues K417N and E484K/A might play a crucial role in antibody evasion, whereas Q498R and N501Y are specifically mutated to strengthen RBD affinity to ACE2 and, thereby, increase the viral effect of the COVID-19 virus.

Changes within the P681 residue of spike dictate cell fusion and syncytia formation of Delta and Omicron variants of SARS-CoV-2 with no effects on neutralization or infectivity

The rapid spread and dominance of the Omicron SARS-CoV-2 lineages have posed severe health challenges worldwide. While extensive research on the role of the Receptor Binding Domain (RBD) in promoting viral infectivity and vaccine sensitivity has been well documented, the functional significance of the ₆₈₁PRRAR/SV₆₈₇ polybasic motif of the viral spike is less clear. In this work, we monitored the infectivity levels and neutralization potential of the wild-type human coronavirus 2019 (hCoV-19), Delta, and Omicron SARS-CoV-2 pseudoviruses against sera samples drawn four months post administration of a third dose of the BNT162b2 mRNA vaccine. Our findings show that in comparison to hCoV-19 and Delta SARS-CoV-2, Omicron lineages BA.1 and BA.2 exhibit enhanced infectivity and a sharp decline in their sensitivity to vaccine-induced neutralizing antibodies. Interestingly, P681 mutations within the viral spike do not play a role in the neutralization potential or infectivity of SARS Cov-2 pseudoviruses carrying mutations in this position. The P681 residue however, dictates the ability of the spike protein to promote fusion and syncytia formation between infected cells. While spike from hCoV-19 (P681) and Omicron (H681) promote only modest cell fusion and formation of syncytia between cells that express the spike-protein, Delta spike (R681) displays enhanced fusogenic activity and promotes syncytia formation. Additional analysis shows that a single P681R mutation within the hCoV-19 spike, or H681R within the Omicron spike, restores fusion potential to similar levels observed for the Delta R681 spike. Conversely, R681P point mutation within the spike of Delta pseudovirus abolishes efficient fusion and syncytia formation. Our investigation also demonstrates that spike proteins from hCoV-19 and Delta SARS-CoV-2 are efficiently incorporated into viral particles relative to the spike of Omicron lineages. We conclude that the third dose of the Pfizer-BNT162b2 provides appreciable protection against the newly emerged Omicron sub-lineages. However, the neutralization sensitivity of these new variants is diminished relative to that of the hCoV-19 or Delta SARS-CoV-2. We further show that the P681 residue within spike dictates cell fusion and syncytia formation with no effects on the infectivity of the specific viral variant and on its sensitivity to vaccine-mediated neutralization.

Potent Omicron-neutralizing antibodies isolated from a patient vaccinated 6 months before Omicron emergence

Therapeutic antibodies are an important tool in the arsenal against coronavirus infection. However, most antibodies developed early in the pandemic have lost most or all efficacy against newly emergent strains of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), particularly those of the Omicron lineage. Here, we report the identification of a panel of vaccinee-derived antibodies that have broad-spectrum neutralization activity. Structural and biochemical characterization of the three broadest-spectrum antibodies reveal complementary footprints and differing requirements for avidity to overcome variant-associated mutations in their binding footprints. In the K18 mouse model of infection, these three antibodies exhibit protective efficacy against BA.1 and BA.2 infection. This study highlights the resilience and vulnerabilities of SARS-CoV-2 antibodies and provides road maps for further development of broad-spectrum therapeutics.

A potent and broad neutralization of SARS-CoV-2 variants of concern by DARPins

We report the engineering and selection of two synthetic proteins-FSR16m and FSR22-for the possible treatment of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. FSR16m and FSR22 are trimeric proteins composed of DARPin SR16m or SR22 fused with a T4 foldon. Despite selection by a spike protein from a now historical SARS-CoV-2 strain, FSR16m and FSR22 exhibit broad-spectrum neutralization of SARS-CoV-2 strains, inhibiting authentic B.1.351, B.1.617.2 and BA.1.1 viruses, with respective IC50 values of 3.4, 2.2 and 7.4 ng ml-1 for FSR16m. Cryo-EM structures revealed that these DARPins recognize a region of the receptor-binding domain (residues 456, 475, 486, 487 and 489) overlapping a critical portion of the angiotensin-converting enzyme 2 (ACE2)-binding surface. K18-hACE2 transgenic mice inoculated with B.1.617.2 and receiving intranasally administered FSR16m showed less weight loss and 10-100-fold lower viral burden in upper and lower respiratory tracts. The strong and broad neutralization potency makes FSR16m and FSR22 promising candidates for the prevention and treatment of infection by SARS-CoV-2.

Assessment of the Biological Impact of SARS-CoV-2 Genetic Variation Using an Authentic Virus Neutralisation Assay with Convalescent Plasma, Vaccinee Sera, and Standard Reagents

In the summer of 2020, it became clear that the genetic composition of SARS-CoV-2 was changing rapidly. This was highlighted by the rapid emergence of the D614G mutation at that time. In the autumn of 2020, the project entitled “Agility” was initiated with funding from the Coalition for Epidemic Preparedness Innovations (CEPI) to assess new variants of SARS-CoV-2. The project was designed to reach out and intercept swabs containing live variant viruses in order to generate highly characterised master and working stocks, and to assess the biological consequences of the rapid genetic changes using both in vitro and in vivo approaches. Since November 2020, a total of 21 variants have been acquired and tested against either a panel of convalescent sera from early in the pandemic, and/or a panel of plasma from triple-vaccinated participants. A pattern of continuous evolution of SARS-CoV-2 has been revealed. Sequential characterisation of the most globally significant variants available to us, generated in real-time, indicated that the most recent Omicron variants appear to have evolved in a manner that avoids immunological recognition by convalescent plasma from the era of the ancestral virus when analysed in an authentic virus neutralisation assay.

Emergence of a unique SARS-CoV-2 Delta sub-cluster harboring a constellation of co-appearing non-Spike mutations

Accumulation of diverse mutations across the structural and nonstructural genes is leading to rapid evolution of SARS-CoV-2, altering its pathogenicity. We performed whole genome sequencing of 239 SARS-CoV-2 RNA samples collected from both adult and pediatric patients across eastern India (West Bengal), during the second pandemic wave in India (April-May 2021). In addition to several common spike mutations within the Delta variant, a unique constellation of eight co-appearing non-Spike mutations was identified, which revealed a high degree of positive mutual correlation. Our results also demonstrated the dynamics of SARS-CoV-2 variants among unvaccinated pediatric patients. 41.4% of our studied Delta strains harbored this signature set of eight co-appearing non-Spike mutations and phylogenetically out-clustered other Delta sub-lineages like 21J, 21A, or 21I. This is the first report from eastern India that portrayed a landscape of co-appearing mutations in the non-Spike proteins, which might have led to the evolution of a distinct Delta subcluster. Accumulation of such mutations in SARS-CoV-2 may lead to the emergence of "vaccine-evading variants." Hence, monitoring of such non-Spike mutations will be significant in the formulation of any future vaccines against those SARS-CoV-2 variants that might evade the current vaccine-induced immunity, among both the pediatric and adult populations.

Higher COVID-19 Vaccination Rates Are Associated with Lower COVID-19 Mortality: A Global Analysis

Mass vaccination initiatives are underway worldwide, and a considerable percentage of the world's population is now vaccinated. This study examined the association of COVID-19 deaths per 1000 cases with a fully vaccinated population. The global median deaths per 1000 cases were 15.68 (IQR 9.84, 25.87) after 6 months of vaccinations and 11.96 (IQR 6.08, 20.63) after 12 months. Across 164 countries, we found significant variations in vaccination levels of populations, booster doses, and mortality, with higher vaccine coverage and lower mortality in high-income countries. Several regression models were performed to test the association between vaccination and COVID-19 mortality. Control variables were used to account for confounding variables. A 10-percentage-point increase in vaccination was associated with an 18.1% decrease in mortality after 6 months (95%CI, 7.4-28.8%) and a 16.8% decrease after 12 months (95%CI, 6.9-26.7%). A 10-percentage-point increase in booster vaccination rates was associated with a 33.1% decrease in COVID-19 mortality (95%CI, 16.0-50.2%). This relationship is present in most analyses by country income groups with variations in the effect size. Efforts are needed to reduce vaccine hesitancy while ensuring suitable infrastructure and supply to enable all countries to increase their vaccination rates.

Case series in Indonesia: B.1.617.2 (delta) variant of SARS-CoV-2 infection after a second dose of vaccine

BACKGROUND

The B.1.617.2 (delta) variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first discovered in Maharashtra in late 2020 and has rapidly expanded across India and worldwide. It took only 2 mo for this variant to spread in Indonesia, making the country the new epicenter of the delta variant as of July 2021. Despite efforts made by accelerating massive rollouts of current vaccines to protect against infection, cases of fully-vaccinated people infected with the delta variant have been reported.

AIM

To describe the demographic statistics and clinical presentation of the delta variant infection after the second dose of vaccine in Indonesia.

METHODS

A retrospective, single-centre case series of the general consecutive population that worked or studied at Faculty of Medicine, Universitas Indonesia with confirmed Delta Variant Infection after a second dose of vaccine from 24 June and 25 June 2021. Cases were collected retrospectively based on a combination of author recall, reverse transcription-polymerase chain reaction (RT-PCR), and whole genome sequencing results from the Clinical Microbiology Laboratory, Faculty of Medicine, Universitas Indonesia.

RESULTS

Between 24 June and 25 June 2021, 15 subjects were confirmed with the B.1.617.2 (delta) variant infection after a second dose of the vaccine. Fourteen subjects were vaccinated with CoronaVac (Sinovac) and one subject with ChAdOx1 nCoV-19 (Oxford-AstraZeneca). All of the subjects remained in home isolation, with fever being the most common symptom at the onset of illness (n = 10, 66.67%). The mean duration of symptoms was 7.73 d (± 5.444). The mean time that elapsed from the first positive swab to a negative RT-PCR test for SARS-CoV-2 was 17.93 d (± 6.3464). The median time that elapsed from the second dose of vaccine to the first positive swab was 87 d (interquartile range: 86-128).

CONCLUSION

Although this case shows that after two doses of vaccine, subjects are still susceptible to the delta variant infection, currently available vaccines remain the most effective protection. They reduce clinical manifestations of COVID-19, decrease recovery time from the first positive swab to negative swab, and lower the probability of hospitalization and mortality rate compared to unvaccinated 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.

Post-vaccination T cell immunity to omicron

In late 2021, the omicron variant of SARS Coronavirus 2 (SARS-CoV-2) emerged and replaced the previously dominant delta strain. Effectiveness of COVID-19 vaccines against omicron has been challenging to estimate in clinical studies or is not available for all vaccines or populations of interest. T cell function can be predictive of vaccine longevity and effectiveness against disease, likely in a more robust way than antibody neutralization. In this mini review, we summarize the evidence on T cell immunity against omicron including effects of boosters, homologous versus heterologous regimens, hybrid immunity, memory responses and vaccine product. Overall, T cell reactivity in post-vaccine specimens is largely preserved against omicron, indicating that vaccines utilizing the parental antigen continue to be protective against disease caused by the omicron variant.

Molecular characteristics, immune evasion, and impact of SARS-CoV-2 variants

The persistent COVID-19 pandemic since 2020 has brought an enormous public health burden to the global society and is accompanied by various evolution of the virus genome. The consistently emerging SARS-CoV-2 variants harboring critical mutations impact the molecular characteristics of viral proteins and display heterogeneous behaviors in immune evasion, transmissibility, and the clinical manifestation during infection, which differ each strain and endow them with distinguished features during populational spread. Several SARS-CoV-2 variants, identified as Variants of Concern (VOC) by the World Health Organization, challenged global efforts on COVID-19 control due to the rapid worldwide spread and enhanced immune evasion from current antibodies and vaccines. Moreover, the recent Omicron variant even exacerbated the global anxiety in the continuous pandemic. Its significant evasion from current medical treatment and disease control even highlights the necessity of combinatory investigation of the mutational pattern and influence of the mutations on viral dynamics against populational immunity, which would greatly facilitate drug and vaccine development and benefit the global public health policymaking. Hence in this review, we summarized the molecular characteristics, immune evasion, and impacts of the SARS-CoV-2 variants and focused on the parallel comparison of different variants in mutational profile, transmissibility and tropism alteration, treatment effectiveness, and clinical manifestations, in order to provide a comprehensive landscape for SARS-CoV-2 variant research.

Potent and pan-neutralization of SARS-CoV-2 variants of concern by DARPins

We report the engineering and selection of two synthetic proteins - FSR16m and FSR22 - for possible treatment of SARS-CoV-2 infection. FSR16m and FSR22 are trimeric proteins composed of DARPin SR16m or SR22 fused with a T4 foldon and exhibit broad spectrum neutralization of SARS-Cov-2 strains. The IC ₅₀ values of FSR16m against authentic B.1.351, B.1.617.2 and BA.1.1 variants are 3.4 ng/mL, 2.2 ng/mL and 7.4 ng/mL, respectively, comparable to currently used therapeutic antibodies. Despite the use of the spike protein from a now historical wild-type virus for design, FSR16m and FSR22 both exhibit increased neutralization against newly-emerged variants of concern (39- to 296-fold) in pseudovirus assays. Cryo-EM structures revealed that these DARPins recognize a region of the receptor binding domain (RBD, residues 455-456, 486-489) overlapping a critical portion of the ACE2-binding surface. K18-hACE2 transgenic mice inoculated with a B.1.617.2 variant and receiving intranasally-administered FSR16m were protected as judged by less weight loss and 10-100-fold reductions in viral burden in the upper and lower respiratory tracts. The strong and broad neutralization potency make FSR16m and FSR22 promising candidates for prevention and treatment of infection by current and potential future strains of SARS-CoV-2.

Real-Word Effectiveness of Global COVID-19 Vaccines Against SARS-CoV-2 Variants: A Systematic Review and Meta-Analysis

Background

Currently, promoted vaccinations against SARS-CoV-2 are being given out globally. However, the occurrence of numerous COVID-19 variants has hindered the goal of rapid mitigation of the COVID-19 pandemic by effective mass vaccinations. The real-word effectiveness of the current vaccines against COVID-19 variants has not been assessed by published reviews. Therefore, our study evaluated the overall effectiveness of current vaccines and the differences between the various vaccines and variants.

Methods

PubMed, Embase, Cochrane Library, medRxiv, bioRxiv, and arXiv were searched to screen the eligible studies. The Newcastle-Ottawa scale and the Egger test were applied to estimate the quality of the literature and any publication bias, respectively. The pooled incident rates of different variants after vaccination were estimated by single-arm analysis. Meanwhile, the pooled efficacies of various vaccines against variants were evaluated by two-arm analysis using odds ratios (ORs) and vaccine effectiveness (VE).

Results

A total of 6,118 studies were identified initially and 44 articles were included. We found that the overall incidence of variants post first/second vaccine were 0.07 and 0.03, respectively. The VE of the incidence of variants post first vaccine between the vaccine and the placebo or unvaccinated population was 40% and post second vaccine was 96%, respectively. The sub-single-arm analysis showed a low prevalence rate of COVID-19 variants after specific vaccination with the pooled incidence below 0.10 in most subgroups. Meanwhile, the sub-two-arm analysis indicated that most current vaccines had a good or moderate preventive effect on certain variants considering that the VE in these subgroups was between 66 and 95%, which was broadly in line with the results of the sub-single-arm analysis.

Conclusion

Our meta-analysis shows that the current vaccines that are used globally could prevent COVID-19 infection and restrict the spread of variants to a great extent. We would also support maximizing vaccine uptake with two doses, as the effectiveness of which was more marked compared with one dose. Although the mRNA vaccine was the most effective against variants according to our study, specific vaccines should be taken into account based on the local dominant prevalence of variants.

Functional Analysis of Spike from SARS-CoV-2 Variants Reveals the Role of Distinct Mutations in Neutralization Potential and Viral Infectivity

Enhanced viral transmission and escape from vaccine–elicited neutralizing antibodies drive worldwide spread of SARS-CoV-2 variants and promote disease progression. However, the impact of specific spike mutations that are carried by different viral variants on viral infectivity and neutralization sensitivity has not been completely defined. Here, we use pseudoviruses to assess the contribution of spike mutations within the Receptor Binding Domain (RBD) and the Furin Cleavage Site (FCS), and appear in circulating viral variants, on viral infectivity and neutralization potential against sera that was drawn from fully vaccinated individuals. Our functional analysis demonstrates that single, P681H, P681R or A701V–FCS mutations do not play a role in viral infectivity and neutralization potential. However, when in conjunction with the RBD–N501Y mutation, viral infectivity is enhanced. Similarly, combining the E484K–RBD mutation to the spike that carries FCS mutations reduces neutralization sensitivity with no effects on viral infectivity. Employing a similar approach onto the spike from Delta or Lota SARS-CoV-2 variants further reveals that specific RBD mutations affect neutralization sensitivity or viral infectivity differently. Our results validate the efficacy of the Pfizer third dose vaccine against Delta and Lota SARS-CoV-2 variants, and outline the significance of distinct RBD mutations in promoting viral infectivity and neutralization sensitivity to post–vaccination sera.

Neutralization of SARS-CoV-2 Omicron by BNT162b2 mRNA vaccine-elicited human sera

The globally circulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant of concern Omicron (B.1.1.529) has a large number of mutations, especially in the spike protein, indicating that recognition by neutralizing antibodies may be compromised. We tested Wuhan (Wuhan-Hu-1 reference strain), Beta (B.1.351), Delta (B.1.617.2), or Omicron pseudoviruses with sera of 51 participants who received two or three doses of the messenger RNA (mRNA)-based COVID-19 vaccine BNT162b2. After two doses, Omicron-neutralizing titers were reduced >22-fold compared with Wuhan-neutralizing titers. One month after the third vaccine dose, Omicron-neutralizing titers were increased 23-fold relative to their levels after two doses and were similar to levels of Wuhan-neutralizing titers after two doses. The requirement of a third vaccine dose to effectively neutralize Omicron was confirmed with sera from a subset of participants using live SARS-CoV-2. These data suggest that three doses of the mRNA vaccine BNT162b2 may protect against Omicron-mediated COVID-19.

The Coronavirus Pandemic – 2022: Viruses, Variants & Vaccines

Since the beginning of the COVID-19 pandemic in 2019–2020, Cytokine & Growth Factor Reviews has published several Special Issues focused on the biology, pathogenesis and therapeutic options in the treatment of COVID-19 infection, including articles on the involvement of the chemokine system in the cytokine storm in COVID-19, intervention in the early stages of COVID-19 pneumonia, the therapeutic value of corticosteroid treatment, early clinical intervention with type 1 interferons, progress in vaccine development, and organ specific complications of COVID-19. By 2022, multiple highly efficacious vaccines are available and are being administered in countries around the world, therapeutic options have been clinically evaluated and approved, and SARS-CoV-2 has arguably become the most thoroughly studied virus in history. But, with progress has also come unanticipated problems – misinformation, anti-vaxxers, opposition to protective masks, and politically motivated interference disguised as knowledge. With this issue of CGFR, we continue to document the global coronavirus pandemic and provide an update on the emergence of viral variants, the global effort to administer vaccines and the impediments to progress posed by misinformation and anti-vaccine sentiment.

Mucosal immune response in BNT162b2 COVID-19 vaccine recipients

BACKGROUND

Although the BNT162b2 COVID-19 vaccine is known to induce IgG neutralizing antibodies in serum protecting against COVID-19, it has not been studied in detail whether it could generate specific immunity at mucosal sites, which represent the primary route of entry of SARS-CoV-2.

METHODS

Samples of serum and saliva of 60 BNT162b2-vaccinated healthcare workers were collected at baseline, two weeks after the first dose and two weeks after the second dose. Anti-S1-protein IgG and IgA total antibodies titres and the presence of neutralizing antibodies against the Receptor Binding Domain in both serum and saliva were measured by quantitative and by competitive ELISA, respectively.

FINDINGS

Complete vaccination cycle generates a high serum IgG antibody titre as a single dose in previously infected seropositive individuals. Serum IgA concentration reaches a plateau after a single dose in seropositive individuals and two vaccine doses in seronegative subjects. After the second dose IgA level was higher in seronegative than in seropositive subjects. In saliva, IgG level is almost two orders of magnitude lower than in serum, reaching the highest values after the second dose. IgA concentration remains low and increases significantly only in seropositive individuals after the second dose. Neutralizing antibody titres were much higher in serum than in saliva.

INTERPRETATION

The mRNA BNT162b2 vaccination elicits a strong systemic immune response by drastically boosting neutralizing antibodies development in serum, but not in saliva, indicating that at least oral mucosal immunity is poorly activated by this vaccination protocol, thus failing in limiting virus acquisition upon its entry through this route.

FUNDING

This work was funded by the Department of Medicine and Surgery, University of Insubria, and partially supported by Fondazione Umberto Veronesi (COVID-19 Insieme per la ricerca di tutti, 2020).

EARLY INTRODUCTION, DISPERSAL AND EVOLUTION OF DELTA SARS-CoV-2 IN SOUTHERN BRAZIL, LATE PREDOMINANCE OF AY.99.2 AND AY.101 RELATED LINEAGES

The emergence of Variants of Concern (VOC) presenting an unusual number of new mutations is one of the most remarkable features of SARS-CoV-2. The Delta variant, since its appearance, replaced the VOC Gamma, which was responsible for the major COVID-19 wave in Brazil. In this study, we performed a Delta whole-genome sequencing of 183 samples as part of a major genomic surveillance study performed since the beginning of the pandemic. Here, we showed an emergence, widespread dispersion and consolidation of the Delta variant in Rio Grande do Sul State, completely replacing the Gamma variant in a four to five months period. Performing the phylogenetic and phylodynamic analysis, the majority of the sequences generated herein were classified as AY.99.2, AY.99.2-like and AY.101. AY.99.2 Delta-related lineage has been widely reported in Brazil and in the Americas as well. Altogether, our findings provided a mutational profile of the sequences and presented high substitutions per site in the root-to-tip phylogenetic tree, corroborating studies that show the high mutational rate of SARS-CoV-2 over time.