Long-Term Persistence of SARS-CoV-2 Neutralizing Antibody Responses After Infection and Estimates of the Duration of Protection (preprint)

The duration of immunity in SARS-CoV-2 infected people remains unclear. Neutralizing antibody responses are the best available correlate of protection against re-infection. Recent studies have estimated that the correlate of 50% protection from re-infection was 20% of the mean convalescent neutralizing antibody titre. We used sera collected from a cohort of 125 individuals with RT-PCR confirmed SARS-CoV-2 infections up to 386 days after symptom onset. In the subset of 65 sera collected from day 151 to 386 after symptom onset, all remained positive in 50% plaque reduction neutralization tests (PRNT50). Because antibody waning follows a bimodal pattern with slower waning beyond day 90 after illness, we fitted lines of decay to 115 sera from 62 patients collected beyond 90 after symptom onset and estimate that PRNT50 antibody will remain detectable for around 1,717 days after symptom onset and that 50% protective antibody titers will be maintained for around 990 days post-symptom onset, in symptomatic patients. Peak PRNT titres in mildly symptomatic children did not differ from those in mildly symptomatic adults but these antibody titres appear to wane faster in children. There was a high level of correlation between PRNT50 antibody titers and the % of inhibition in surrogate virus neutralization tests. We conclude that there will be relatively long-lived protection from re-infection following symptomatic COVID-19 disease.Funding Information: The study was supported by the Health and Medical Research Fund, Commissioned research on Novel Coronavirus Disease (COVID-19) (Reference no COVID190126) from the Food and Health Bureau, Hong Kong SAR Government and the Theme-based Research Scheme project no. T11-712/19-N, the University Grants Committee of the Hong Kong Government.Declaration of Interests: None of the authors have any conflicts of interest to declare.Ethics Approval Statement: Written informed consent was obtained from the participants or their parents (when the participant was a child) and the studies were approved by the institutional review boards of the respective hospitals, viz. Kowloon West Cluster (KW/EX-20-039 (144-27)), Kowloon Central / Kowloon East cluster (KC/KE-20-0154/ER2) and HKU/HA Hong Kong West Cluster (UW 20-273).

SARS-CoV-2 specific T cell responses are lower in children and increase with age and time after infection (preprint)

SARS-CoV-2 infection of children leads to a mild illness and the immunological differences with adults remains unclear. We quantified the SARS-CoV-2 specific T cell responses in adults and children (<13 years of age) with RT-PCR confirmed asymptomatic and symptomatic infection for long-term memory, phenotype and polyfunctional cytokines. Acute and memory CD4 + T cell responses to structural SARS-CoV-2 proteins significantly increased with age, whilst CD8 + T cell responses increased with time post infection. Infected children had significantly lower CD4 + and CD8 + T cell responses to SARS-CoV-2 structural and ORF1ab proteins compared to infected adults. SARS-CoV-2-specific CD8 + T cell responses were comparable in magnitude to uninfected negative adult controls. In infected adults CD4 + T cell specificity was skewed towards structural peptides, whilst children had increased contribution of ORF1ab responses. This may reflect differing T cell compartmentalisation for antigen processing during antigen exposure or lower recruitment of memory populations. T cell polyfunctional cytokine production was comparable between children and adults, but children had a lower proportion of SARS-CoV-2 CD4 + T cell effector memory. Compared to adults, children had significantly lower levels of antibodies to β-coronaviruses, indicating differing baseline immunity. Total T follicular helper responses was increased in children during acute infection indicating rapid co-ordination of the T and B cell responses. However total monocyte responses were reduced in children which may be reflective of differing levels of inflammation between children and adults. Therefore, reduced prior β-coronavirus immunity and reduced activation and recruitment of de novo responses in children may drive milder COVID-19 pathogenesis.

The SARS-CoV-2 antibody landscape is lower in magnitude for structural proteins, diversified for accessory proteins and stable long-term in children (preprint)

BackgroundChildren are less clinically affected by SARS-CoV-2 infection than adults with the majority of cases being mild or asymptomatic and the differences in infection outcomes are poorly understood. The kinetics, magnitude and landscape of the antibody response may impact the clinical severity and serological diagnosis of COVID-19. Thus, a comprehensive investigation of the antibody landscape in children and adults is needed. MethodsWe tested 254 plasma from 122 children with symptomatic and asymptomatic SARS-CoV-2 infections in Hong Kong up to 206 days post symptom onset, including 146 longitudinal samples from 58 children. Adult COVID-19 patients and pre-pandemic controls were included for comparison. We assessed antibodies to a 14-wide panel of SARS-CoV-2 structural and accessory proteins by Luciferase Immunoprecipitation System (LIPS). FindingsChildren have lower levels of Spike and Nucleocapsid antibodies than adults, and their cumulative humoral response is more expanded to accessory proteins (NSP1 and Open Reading Frames (ORFs)). Sensitive serology using the three N, ORF3b, ORF8 antibodies can discriminate COVID-19 in children. Principal component analysis revealed distinct serological signatures in children and the highest contribution to variance were responses to non-structural proteins ORF3b, NSP1, ORF7a and ORF8. Longitudinal sampling revealed maintenance or increase of antibodies for at least 6 months, except for ORF7b antibodies which showed decline. It was interesting to note that children have higher antibody responses towards known IFN antagonists: ORF3b, ORF6 and ORF7a. The diversified SARS-CoV-2 antibody response in children may be an important factor in driving control of SARS-CoV-2 infection.