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Conjunctival and nasal mucosal antibody responses in thirty-four paediatric and forty-seven adult COVID-19 patients were measured. The mucosal antibody was IgA dominant. In the nasal epithelial lining fluid (NELF) of asymptomatic paediatric patients, SARS-CoV-2 spike protein 1 (S1) specific immunoglobulin A (IgA) was induced early. Their plasma S1-specific IgG levels were higher than symptomatic patients. More adult with mild disease had NELF S1-specific IgA than those with severe/critical illness. Within the first week of diagnosis, higher S1-specific antibodies in NELF and plasma and lower vial loads were detected in paediatric than adult patients with mild disease. The IgA and IgG levels correlated positively with the surrogate neutralization readout. The detectable NELF ‘neutralizing’ S1-specific IgA in the first week after diagnosis correlated with a rapid decline in viral load. This study highlights the effect of nasal IgA in limiting the SARS-CoV-2 replication and provides complementary information to the serum antibody measurements.

BackgroundInvestigations of the natural viral interference effect between rhinovirus (RV) and influenza virus (IV) were conducted in temperate regions. We conducted an epidemiological study in Hong Kong, a major epicentre of influenza virus in the sub-tropical region. RV is the most prevalent respiratory virus year-round and causes asymptomatic to mild symptoms while IV infection exerts a great burden of public health. We aimed to examine the correlation of RV prevalence against IV activity.MethodsNasopharyngeal aspirates (NPA) collected from patients hospitalized in the regional hospitals from 2015 to 2019 were examined for the presence of respiratory viruses. The correlation of the monthly prevalence between all pairs of virus infection, the co-infection rate and the temporal interference of RV and IV were tested. The viral interference was validatedin vitroby conducting sequential RV and IV infection in the well-differentiated primary human airway epithelial cells.FindingsA total of 112,926 NPA were evaluated, and the Enterovirus/RV was the most prevalent respiratory virus detected. The negative correlation between EV/RV and IVs prevalence was independent of age and meteorological factors. Co-infection of EV/RV and IV was significantly less when compared with other virus pairs. Prior exposure to RV inhibited the replication of influenza A, B and oseltamivir-resistance stainin vitroand the inhibition is replication dependent.InterpretationEpidemiological surveillance and the sequential infectionin vitrosuggested viral interference between EV/RV and IV operated at the population, individual and cellular levels.FundingThis study was supported by the General Research Fund (Ref: 24107017 and 14103119 to RWYC), Health and Medical Research Fund (Ref: COVID190112 to RWYC) and the Chinese University Direct Grant for Research (Ref: 2019.073 to RWYC).