SARS-CoV-2 accessory proteins reveal distinct serological signatures in children

Characterization of humoral immune responses against SARS-CoV-2 accessory proteins in infected patients and mouse model

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19, encodes several accessory proteins that have been shown to play crucial roles in regulating the innate immune response. However, their expressions in infected cells and immunogenicity in infected humans and mice are still not fully understood. This study utilized various techniques such as luciferase immunoprecipitation system (LIPS), immunofluorescence ​assay (IFA), and western ​blot (WB) to detect accessory protein-specific antibodies in sera of COVID-19 patients. Specific antibodies to proteins 3a, 3b, 7b, 8 and 9c can be detected by LIPS, but only protein 3a antibody was detected by IFA or WB. Antibodies against proteins 3a and 7b were only detected in ICU patients, which may serve as a marker for predicting disease progression. Further, we investigated the expression of accessory proteins in SARS-CoV-2-infected cells and identified the expressions of proteins 3a, 6, 7a, 8, and 9b. We also analyzed their ability to induce antibodies in immunized mice and found that only proteins 3a, 6, 7a, 8, 9b and 9c were able to induce measurable antibody productions, but these antibodies lacked neutralizing activities and did not protect mice from SARS-CoV-2 infection. Our findings validate the expression of SARS-CoV-2 accessory proteins and elucidate their humoral immune response, providing a basis for protein detection assays and their role in pathogenesis.

Inferring Incidence of Unreported SARS-CoV-2 Infections Using Seroprevalence of Open Reading Frame 8 Antigen, Hong Kong

We tested seroprevalence of open reading frame 8 antigens to infer the number of unrecognized SARS-CoV-2 Omicron infections in Hong Kong during 2022. We estimate 33.6% of the population was infected, 72.1% asymptomatically. Surveillance and control activities during large-scale outbreaks should account for potentially substantial undercounts.

Serological assays for differentiating natural COVID-19 infection from vaccine induced immunity

BACKGROUND

Natural SARS-CoV-2 infection may elicit antibodies to a range of viral proteins including non-structural protein ORF8. RNA, adenovirus vectored and sub-unit vaccines expressing SARS-CoV-2 spike would be only expected to elicit S-antibodies and antibodies to distinct domains of nucleocapsid (N) protein may reliably differentiate infection from vaccine-elicited antibody. However, inactivated whole virus vaccines may potentially elicit antibody to wider range of viral proteins, including N protein. We hypothesized that antibody to ORF8 protein will discriminate natural infection from vaccination irrespective of vaccine type.

METHODS

We optimized and validated the anti-ORF8 and anti-N C-terminal domain (NCTD) ELISA assays using sera from pre-pandemic, RT-PCR confirmed natural infection sera and BNT162b2 (BNT) or CoronaVac vaccinees. We then applied these optimized assays to a cohort of blood donor sera collected in April-July 2022 with known vaccination and self-reported infection status.

RESULTS

We optimized cut-off values for the anti-ORF8 and anti-N-CTD IgG ELISA assays using receiver-operating-characteristic (ROC) curves. The sensitivity of the anti-ORF8 and anti-N-CTD ELISA for detecting past infection was 83.2% and 99.3%, respectively. Specificity of anti-ORF8 ELISA was 96.8 % vs. the pre-pandemic cohort or 93% considering the pre-pandemic and vaccine cohorts together. The anti-N-CTD ELISA specificity of 98.9% in the pre-pandemic cohort, 93% in BNT vaccinated and only 4 % in CoronaVac vaccinated cohorts. Anti-N-CTD antibody was longer-lived than anti-ORF8 antibody after natural infection.

CONCLUSIONS

Anti-N-CTD antibody assays provide good discrimination between natural infection and vaccination in BNT162b2 vaccinated individuals. Anti-ORF8 antibody can help discriminate infection from vaccination in either type of vaccine and help estimate infection attack rates (IAR) in communities.

ORF3c is expressed in SARS-CoV-2-infected cells and inhibits innate sensing by targeting MAVS

Most SARS-CoV-2 proteins are translated from subgenomic RNAs (sgRNAs). While the majority of these sgRNAs are monocistronic, some viral mRNAs encode more than one protein. One example is the ORF3a sgRNA that also encodes ORF3c, an enigmatic 41-amino-acid peptide. Here, we show that ORF3c is expressed in SARS-CoV-2-infected cells and suppresses RIG-I- and MDA5-mediated IFN-β induction. ORF3c interacts with the signaling adaptor MAVS, induces its C-terminal cleavage, and inhibits the interaction of RIG-I with MAVS. The immunosuppressive activity of ORF3c is conserved among members of the subgenus sarbecovirus, including SARS-CoV and coronaviruses isolated from bats. Notably, however, the SARS-CoV-2 delta and kappa variants harbor premature stop codons in ORF3c, demonstrating that this reading frame is not essential for efficient viral replication in vivo and is likely compensated by other viral proteins. In agreement with this, disruption of ORF3c does not significantly affect SARS-CoV-2 replication in CaCo-2, CaLu-3, or Rhinolophus alcyone cells. In summary, we here identify ORF3c as an immune evasion factor of SARS-CoV-2 that suppresses innate sensing in infected cells.

Humoral immune response to SARS-CoV-2 and endemic coronaviruses in urban and indigenous children in Colombia

BACKGROUND

Although anti-SARS-CoV-2 humoral immune responses and epidemiology have been extensively studied, data gaps remain for certain populations such as indigenous people or children especially in low- and middle-income countries. To address this gap, we evaluated SARS-CoV-2 seroprevalence and humoral immunity towards the parental B.1 strain, local SARS-CoV-2 variants, and endemic coronaviruses in children from Colombia from March to April 2021.

METHODS

We performed a cross-sectional seroprevalence study with 80 children from Bogotá and expanded our analysis by comparing results with an independent observational study of 82 children from the Wiwa community living in the north-eastern Colombian territories. Antibody IgG titers towards SARS-CoV-2 and the endemic coronaviruses as well as ACE2 binding inhibition as a proxy for neutralization towards several SARS-CoV-2 variants were analyzed using two multiplex-based immunoassays.

RESULTS

While we find seroprevalence estimates of 21.3% in children from Bogotá, seroprevalence is higher with 34.1% in Wiwa children. We observe a robust induction of antibodies towards the surface-exposed spike protein, its S1-, S2- and receptor-binding-subdomains in all SARS-CoV-2 seropositive children. Only nucleocapsid-specific IgG is significantly lower in the indigenous participants. ACE2 binding inhibition is low for all SARS-CoV-2 variants examined. We observe a dominance of NL63 S1 IgG levels in urban and indigenous children which suggests an early exposure to this respiratory virus independent of living conditions and geographic location. SARS-CoV-2 seropositivity does not correlate with antibody levels towards any of the four endemic coronaviruses indicating the absence of cross-protective immunity.

CONCLUSIONS

Overall, antibody titers, but in particular ACE2 binding inhibition are low within Colombian samples, requiring further investigation to determine any potential clinical significance.

Distinguishing SARS-CoV-2 infection and vaccine responses up to 18 months post-infection using nucleocapsid protein and receptor-binding domain antibodies

The prediction of the durability of immunity against COVID-19 is relevant, and longitudinal studies are essential for unraveling the details regarding protective SARS-CoV-2 antibody responses. It has become challenging to discriminate between COVID-19 vaccine- and infection-induced immune responses since all approved vaccines in Europe and the USA are based on the viral spike (S) protein, which is also the most commonly used antigen in immunoassays measuring immunoglobulins (Igs) against SARS-CoV-2. We have developed a nucleocapsid (N) protein-based sandwich ELISA for detecting pan anti-SARS-CoV-2 Ig with a sensitivity and specificity of 97%. Generalized mixed models were used to determine the degree of long-term humoral immunity against the N protein and the receptor-binding domain (RBD) of the S protein in a cohort of infected individuals to distinguish between COVID-19 vaccine- and infection-induced immunity. N-specific waning could be observed in individuals who did not experience reinfection, while individuals who experienced reinfection had a new significant increase in N-specific Ig levels. In individuals that seroconverted without a reinfection, 70.1% remained anti-N seropositive after 550 days. The anti-RBD Ig dynamics were unaffected by reinfection but exhibited a clear increase in RBD-specific Ig when vaccination was initiated. In conclusion, a clear difference in the dynamics of the antibody response against N protein and RBD was observed over time. Anti-N protein-specific Igs can be detected up to 18 months after SARS-CoV-2 infection allowing long-term discrimination of infectious and vaccine antibody responses.IMPORTANCELongitudinal studies are essential to unravel details regarding the protective antibody responses after COVID-19 infection and vaccination. It has become challenging to distinguish long-term immune responses to SARS-CoV-2 infection and vaccination since most approved vaccines are based on the viral spike (S) protein, which is also mostly used in immunoassays measuring immunoglobulins (Igs) against SARS-CoV-2. We have developed a novel nucleocapsid (N) protein-based sandwich ELISA for detecting pan-anti-SARS-CoV-2 Ig, exhibiting high sensitivity and specificity. Generalized mixed models were used to determine long-term humoral immunity in a cohort of infected individuals from the Faroe Islands, distinguishing between COVID-19 vaccine- and infection-induced immunity. A clear difference in the dynamics of the antibody response against N protein and S protein was observed over time, and the anti-N protein-specific Igs could be detected up to 18 months after SARS-CoV-2 infection. This enables long-term discrimination between natural infection and vaccine-dependent antibody responses.

SARS-CoV-2 serology in pediatrics: Seroprevalence studies in unvaccinated children and humoral antibody response post vaccination

BACKGROUND

Humoral response against SARS-CoV-2 is increasingly accepted as the central correlate of immune protection. Recent pediatric seroprevalence data are extremely limited. Significant knowledge gaps also exist in immune response to mRNA SARS-CoV-2 vaccination in children. As children demonstrate distinct response to naïve infection relative to adults, it is essential to investigate age-specific differences in seroprevalence and antibody response to SARS-CoV-2 vaccination.

METHODS

Seroprevalence was assessed through two cross-sectional serosurveys prior to COVID-19 vaccination approval in children <5 years using residual patient specimens (n = 2902). To assess antibody response post-vaccination, 842 participants (580 children, 262 adults) were prospectively recruited with informed consent. Participation required completion of a health questionnaire and blood donation. Samples were collected at varying times post-vaccination and assayed using the Abbott AdviseDx SARS-CoV-2 IgG II and DiaSorin LIAISON SARS-CoV-2 TrimericS IgG assays.

RESULTS

Significant increases in seroprevalence were observed between the first and second serosurveys in unvaccinated children <6 months to 5 years (38-75%). In the prospective vaccination cohort, serokinetic response decreased with time post-dose of an mRNA vaccine. Measured IgG titres were significantly higher in children relative to adults across all time points.

CONCLUSIONS

This is the largest evaluation of quantitative SARS-CoV-2 antibody assays in a cohort of Canadian children, adolescents, and adults. Findings suggest high rates of SARS-CoV-2 exposure among unvaccinated young children in the Toronto community. Additional data supports children have higher antibody titres relative to adults post-vaccination.

Elevated binding and functional antibody responses to SARS-CoV-2 in infants versus mothers

Infant antibody responses to viral infection can differ from those in adults. However, data on the specificity and function of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies in infants, and direct comparisons between infants and adults are limited. Here, we characterize antibody binding and functionality against Wuhan-Hu-1 (B lineage) strain SARS-CoV-2 in convalescent plasma from 36 postpartum women and 14 of their infants infected with SARS-CoV-2 from a vaccine-naïve prospective cohort in Nairobi, Kenya. We find significantly higher antibody titers against SARS-CoV-2 Spike, receptor binding domain and N-terminal domain, and Spike-expressing cell-surface staining levels in infants versus mothers. Plasma antibodies from mothers and infants bind to similar regions of the Spike S2 subunit, including the fusion peptide (FP) and stem helix-heptad repeat 2. However, infants display higher antibody levels and more consistent antibody escape pathways in the FP region compared to mothers. Finally, infants have significantly higher levels of antibody-dependent cellular cytotoxicity (ADCC), though, surprisingly, Spike pseudovirus neutralization titers between infants and mothers are similar. These results suggest infants develop distinct SARS-CoV-2 binding and functional antibody activities and reveal age-related differences in humoral immunity to SARS-CoV-2 infection that could be relevant to protection and COVID-19 disease outcomes.

Policies on children and schools during the SARS-CoV-2 pandemic in Western Europe

During the pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), mitigation policies for children have been a topic of considerable uncertainty and debate. Although some children have co-morbidities which increase their risk for severe coronavirus disease (COVID-19), and complications such as multisystem inflammatory syndrome and long COVID, most children only get mild COVID-19. On the other hand, consistent evidence shows that mass mitigation measures had enormous adverse impacts on children. A central question can thus be posed: What amount of mitigation should children bear, in response to a disease that is disproportionally affecting older people? In this review, we analyze the distinct child versus adult epidemiology, policies, mitigation trade-offs and outcomes in children in Western Europe. The highly heterogenous European policies applied to children compared to adults did not lead to significant measurable differences in outcomes. Remarkably, the relative epidemiological importance of transmission from school-age children to other age groups remains uncertain, with current evidence suggesting that schools often follow, rather than lead, community transmission. Important learning points for future pandemics are summarized.

Immunization with Recombinant Accessory Protein-Deficient SARS-CoV-2 Protects against Lethal Challenge and Viral Transmission

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to a worldwide coronavirus disease 2019 (COVID-19) pandemic. Despite the high efficacy of the authorized vaccines, there may be uncertain and unknown side effects or disadvantages associated with current vaccination approaches. Live-attenuated vaccines (LAVs) have been shown to elicit robust and long-term protection by the induction of host innate and adaptive immune responses. In this study, we sought to verify an attenuation strategy by generating 3 double open reading frame (ORF)-deficient recombinant SARS-CoV-2s (rSARS-CoV-2s) simultaneously lacking two accessory ORF proteins (ORF3a/ORF6, ORF3a/ORF7a, and ORF3a/ORF7b). We report that these double ORF-deficient rSARS-CoV-2s have slower replication kinetics and reduced fitness in cultured cells compared with their parental wild-type (WT) counterpart. Importantly, these double ORF-deficient rSARS-CoV-2s showed attenuation in both K18 hACE2 transgenic mice and golden Syrian hamsters. A single intranasal dose vaccination induced high levels of neutralizing antibodies against SARS-CoV-2 and some variants of concern and activated viral component-specific T cell responses. Notably, double ORF-deficient rSARS-CoV-2s were able to protect, as determined by the inhibition of viral replication, shedding, and transmission, against challenge with SARS-CoV-2 in both K18 hACE2 mice and golden Syrian hamsters. Collectively, our results demonstrate the feasibility of implementing the double ORF-deficient strategy to develop safe, immunogenic, and protective LAVs to prevent SARS-CoV-2 infection and associated COVID-19. IMPORTANCE Live-attenuated vaccines (LAVs) are able to induce robust immune responses, including both humoral and cellular immunity, representing a very promising option to provide broad and long-term immunity. To develop LAVs for SARS-CoV-2, we engineered attenuated recombinant SARS-CoV-2 (rSARS-CoV-2) that simultaneously lacks the viral open reading frame 3a (ORF3a) in combination with either ORF6, ORF7a, or ORF7b (Δ3a/Δ6, Δ3a/Δ7a, and Δ3a/Δ7b, respectively) proteins. Among them, the rSARS-CoV-2 Δ3a/Δ7b was completely attenuated and able to provide 100% protection against an otherwise lethal challenge in K18 hACE2 transgenic mice. Moreover, the rSARS-CoV-2 Δ3a/Δ7b conferred protection against viral transmission between golden Syrian hamsters.

Viral immunity: Basic mechanisms and therapeutic applications-a Keystone Symposia report

Viruses infect millions of people each year. Both endemic viruses circulating throughout the population as well as novel epidemic and pandemic viruses pose ongoing threats to global public health. Developing more effective tools to address viruses requires not only in-depth knowledge of the virus itself but also of our immune system's response to infection. On June 29 to July 2, 2022, researchers met for the Keystone symposium "Viral Immunity: Basic Mechanisms and Therapeutic Applications." This report presents concise summaries from several of the symposium presenters.

Advancing Luciferase-Based Antibody Immunoassays to Next-Generation Mix and Read Testing

Antibody measurements play a central role in the diagnosis of many autoimmune and infectious diseases. One antibody detection technology, Luciferase Immunoprecipitation Systems (LIPS), utilizes genetically encoded recombinant luciferase antigen fusion proteins in an immunoglobulin capture format to generate robust antibody measurement with high diagnostic sensitivity and specificity. The LIPS technology has been highly useful in detecting antibodies for research diagnostics and the discovery of new autoantigens. The methodology of the assay requires immunoglobulin binding reagents such as protein A/G beads and washing steps to process the immune complex before antibody levels are measured by light production with a luminometer. Recently, simplified mix and read immunoassays based on split components of the nanoluciferase enzyme in a complementation format have been developed for antibody measurements without requiring immunoglobulin-capturing beads or washing steps. The mix and read immunoassays utilize two or three nanoluciferase fragments which when reconstituted via antigen-specific antibody binding generate a functional enzyme. At present, these split luciferase tests have been developed mainly for detecting SARS-CoV-2 antibodies. Here, we describe the traditional LIPS technology and compare it to the new split luciferase methodologies focusing on their technical features, strengths, limitations, and future opportunities for diagnostic research, and clinical applications.

Immune profiling of SARS-CoV-2 epitopes in asymptomatic and symptomatic pediatric and adult patients

BACKGROUND

The infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has unpredictable manifestations of coronavirus disease (COVID-19) and variable clinical course with some patients being asymptomatic whereas others experiencing severe respiratory distress, or even death. We aimed to evaluate the immunoglobulin G (IgG) response towards linear peptides on a peptide array containing sequences from SARS-CoV-2, Middle East respiratory syndrome-related coronavirus (MERS) and common-cold coronaviruses 229E, OC43, NL63 and HKU1 antigens, in order to identify immunological indicators of disease outcome in SARS-CoV-2 infected patients.

METHODS

We included in the study 79 subjects, comprising 19 pediatric and 30 adult SARS-CoV-2 infected patients with increasing disease severity, from mild to critical illness, and 30 uninfected subjects who were vaccinated with one dose of SARS-CoV-2 spike mRNA BNT162b2 vaccine. Serum samples were analyzed by a peptide microarray containing 5828 overlapping 15-mer synthetic peptides corresponding to the full SARS-CoV-2 proteome and selected linear epitopes of spike (S), envelope (E) and membrane (M) glycoproteins as well as nucleoprotein (N) of MERS, SARS and coronaviruses 229E, OC43, NL63 and HKU1 (isolates 1, 2 and 5).

RESULTS

All patients exhibited high IgG reactivity against the central region and C-terminus peptides of both SARS-CoV-2 N and S proteins. Setting the threshold value for serum reactivity above 25,000 units, 100% and 81% of patients with severe disease, 36% and 29% of subjects with mild symptoms, and 8% and 17% of children younger than 8-years reacted against N and S proteins, respectively. Overall, the total number of peptides in the SARS-CoV-2 proteome targeted by serum samples was much higher in children compared to adults. Notably, we revealed a differential antibody response to SARS-CoV-2 peptides of M protein between adults, mainly reacting against the C-terminus epitopes, and children, who were highly responsive to the N-terminus of M protein. In addition, IgG signals against NS7B, NS8 and ORF10 peptides were found elevated mainly among adults with mild (63%) symptoms. Antibodies towards S and N proteins of other coronaviruses (MERS, 229E, OC43, NL63 and HKU1) were detected in all groups without a significant correlation with SARS-CoV-2 antibody levels.

CONCLUSIONS

Overall, our results showed that antibodies elicited by specific linear epitopes of SARS-CoV-2 proteome are age dependent and related to COVID-19 clinical severity. Cross-reaction of antibodies to epitopes of other human coronaviruses was evident in all patients with distinct profiles between children and adult patients. Several SARS-CoV-2 peptides identified in this study are of particular interest for the development of vaccines and diagnostic tests to predict the clinical outcome of SARS-CoV-2 infection.

Elevated binding and functional antibody responses to SARS-CoV-2 in infants versus mothers

Infant antibody responses to viral infection can differ from those in adults. However, data on the specificity and function of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies in infants, and direct comparisons between infants and adults are limited. We characterized antibody binding and functionality in convalescent plasma from postpartum women and their infants infected with SARS-CoV-2 from a vaccine-naïve prospective cohort in Nairobi, Kenya. Antibody titers against SARS-CoV-2 Spike, receptor binding domain and N-terminal domain, and Spike-expressing cell-surface staining levels were significantly higher in infants than in mothers. Plasma antibodies from mothers and infants bound to similar regions of the Spike S2 subunit, including the fusion peptide (FP) and stem helix-heptad repeat 2. However, infants displayed higher antibody levels and more consistent antibody escape pathways in the FP region compared to mothers. Finally, infants had significantly higher levels of antibody-dependent cellular cytotoxicity (ADCC), though, surprisingly, neutralization titers between infants and mothers were similar. These results suggest infants develop distinct SARS-CoV-2 binding and functional antibody repertoires and reveal age-related differences in humoral immunity to SARS-CoV-2 infection that could be relevant to protection and COVID-19 disease outcomes.

Real-world COVID-19 vaccine effectiveness against the Omicron BA.2 variant in a SARS-CoV-2 infection-naive population

The SARS-CoV-2 Omicron variant has demonstrated enhanced transmissibility and escape of vaccine-derived immunity. Although first-generation vaccines remain effective against severe disease and death, robust evidence on vaccine effectiveness (VE) against all Omicron infections, irrespective of symptoms, remains sparse. We used a community-wide serosurvey with 5,310 subjects to estimate how vaccination histories modulated risk of infection in infection-naive Hong Kong during a large wave of Omicron BA.2 epidemic in January-July 2022. We estimated that Omicron infected 45% (41-48%) of the local population. Three and four doses of BNT162b2 or CoronaVac were effective against Omicron infection 7 days after vaccination (VE of 48% (95% credible interval 34-64%) and 69% (46-98%) for three and four doses of BNT162b2, respectively; VE of 30% (1-66%) and 56% (6-97%) for three and four doses of CoronaVac, respectively). At 100 days after immunization, VE waned to 26% (7-41%) and 35% (10-71%) for three and four doses of BNT162b2, and to 6% (0-29%) and 11% (0-54%) for three and four doses of CoronaVac. The rapid waning of VE against infection conferred by first-generation vaccines and an increasingly complex viral evolutionary landscape highlight the necessity for rapidly deploying updated vaccines followed by vigilant monitoring of VE.

The clinical characteristics of pediatric patients infected by SARS-CoV-2 Omicron variant and whole viral genome sequencing analysis

Pediatric population was generally less affected clinically by SARS-CoV-2 infection. Few pediatric cases of COVID-19 have been reported compared to those reported in infected adults. However, a rapid increase in the hospitalization rate of SARS-CoV-2 infected pediatric patients was observed during Omicron variant dominated COVID-19 outbreak. In this study, we analyzed the B.1.1.529 (Omicron) genome sequences collected from pediatric patients by whole viral genome amplicon sequencing using Illumina next generation sequencing platform, followed by phylogenetic analysis. The demographic, epidemiologic and clinical data of these pediatric patients are also reported in this study. Fever, cough, running nose, sore throat and vomiting were the more commonly reported symptoms in children infected by Omicron variant. A novel frameshift mutation was found in the ORF1b region (NSP12) of the genome of Omicron variant. Seven mutations were identified in the target regions of the WHO listed SARS-CoV-2 primers and probes. On protein level, eighty-three amino acid substitutions and fifteen amino acid deletions were identified. Our results indicate that asymptomatic infection and transmission among children infected by Omicron subvariants BA.2.2 and BA.2.10.1 are not common. Omicron may have different pathogenesis in pediatric population.

Comparison of antibody responses to SARS-CoV-2 variants in Australian children

There is limited understanding of antibody responses in children across different SARS-CoV-2 variants. As part of an ongoing household cohort study, we assessed the antibody response among unvaccinated children infected with Wuhan, Delta, or Omicron variants, as well as vaccinated children with breakthrough Omicron infection, using a SARS-CoV-2 S1-specific IgG assay and surrogate virus neutralization test (% inhibition). Most children infected with Delta (100%, 35/35) or Omicron (81.3%, 13/16) variants seroconverted by one month following infection. In contrast, 37.5% (21/56) children infected with Wuhan seroconverted, as previously reported. However, Omicron-infected children (geometric mean concentration 46.4 binding antibody units/ml; % inhibition = 16.3%) mounted a significantly lower antibody response than Delta (435.5 binding antibody untis/mL, % inhibition = 76.9%) or Wuhan (359.0 binding antibody units/mL, % inhibition = 74.0%). Vaccinated children with breakthrough Omicron infection mounted the highest antibody response (2856 binding antibody units/mL, % inhibition = 96.5%). Our findings suggest that despite a high seropositivity rate, Omicron infection in children results in lower antibody levels and function compared with Wuhan or Delta infection or with vaccinated children with breakthrough Omicron infection. Our data have important implications for public health measures and vaccination strategies to protect children.

Development of a highly sensitive Gaussia luciferase immunoprecipitation assay for the detection of antibodies against African swine fever virus

In recent years, African swine fever (ASF) has caused a devastating blow to the swine industry globally. Since no effective vaccine is available, strict biosafety measures and rapid diagnosis are the most effective strategies for ASF control. ASFV p30 is one of the most antigenic viral proteins that have been widely used in the field for serological diagnosis of ASF infection. In this study, we developed a luciferase immunoprecipitation system (LIPS) assay for the detection of ASFV antibodies in pig serum using Gaussia luciferase (GLuc)-tagged p30 as a diagnostic antigen. The optimal GLuc-p30 input of 10⁷ luminance units (LU) and optimal serum dilution factor of 1/100 were set to achieve the highest P/N ratio. Based on 87 ASFV-positive and negative pig sera, the cutoff value of the S/N ratio could be set between 2.298 and 30.59 to achieve 100% sensitivity and 100% specificity. Moreover, the diagnostic sensitivity of this LIPS is comparable to that of a commercial enzyme-linked immunosorbent assay (ELISA) and the specificity of LIPS is even superior to the tested ELISA. In conclusion, we have established a LIPS assay for ASFV antibody detection, which could be a potential method for ASFV diagnosis in laboratories and farms.

Immunogenicity and reactogenicity of SARS-CoV-2 vaccines BNT162b2 and CoronaVac in healthy adolescents

We present an interim analysis of a registered clinical study (NCT04800133) to establish immunobridging with various antibody and cellular immunity markers and to compare the immunogenicity and reactogenicity of 2-dose BNT162b2 and CoronaVac in healthy adolescents as primary objectives. One-dose BNT162b2, recommended in some localities for risk reduction of myocarditis, is also assessed. Antibodies and T cell immune responses are non-inferior or similar in adolescents receiving 2 doses of BNT162b2 (BB, N = 116) and CoronaVac (CC, N = 123) versus adults after 2 doses of the same vaccine (BB, N = 147; CC, N = 141) but not in adolescents after 1-dose BNT162b2 (B, N = 116). CC induces SARS-CoV-2 N and N C-terminal domain seropositivity in a higher proportion of adolescents than adults. Adverse reactions are mostly mild for both vaccines and more frequent for BNT162b2. We find higher S, neutralising, avidity and Fc receptor-binding antibody responses in adolescents receiving BB than CC, and a similar induction of strong S-specific T cells by the 2 vaccines, in addition to N- and M-specific T cells induced by CoronaVac but not BNT162b2, possibly implying differential durability and cross-variant protection by BNT162b2 and CoronaVac, the 2 most used SARS-CoV-2 vaccines worldwide. Our results support the use of both vaccines in adolescents.

There are adverse events associated with COVID-19 vaccines, such as myocarditis for adolescents following receipt of SARS-CoV-2 mRNA vaccines. Here the authors compare the immunogenicity and reactogenicity of two widely available SARS-CoV-2 vaccines (BNT162b2, an mRNA vaccine, and CoronaVac, a whole-virus inactivated vaccine) in healthy adolescents.