ABSTRACT
Monitoring population protective immunity against SARS-CoV-2 variants is critical for risk assessment. In this serosurveillance study, older adults show much lower seropositive rates of neutralizing antibody (NAb) against ancestral virus than the younger population. The increase in NAb seopositive rate generally follows the population vaccination uptake rate, but older adults have a much lower NAb seropositive rate than vaccination uptake rate. For all age groups, the seropositive rates of NAb against Omicron variant are much lower than those against the ancestral virus. During the fifth wave of COVID-19 in Hong Kong which is dominated by Omicron sublineage BA.2, the case-fatality rate is exceptionally high in the ≥80 year-old age group (9.2%). Our study suggests that the severe BA.2 outbreak in Hong Kong can be attributed by the lack of protective immunity in the population, especially among the vulnerable older adults, and highlights the importance of continual surveillance of protective immunity against emerging variants of SARS-CoV-2.
Subject(s)
COVID-19ABSTRACT
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is transmitted largely by respiratory droplets or airborne aerosols. Despite being frequently found in the immediate environment and faeces of patients, evidence supporting oral acquisition of SARS-CoV-2 is unavailable. Utilizing Syrian hamster model, we demonstrated that the severity of pneumonia induced by intranasal inhalation of SARS-CoV-2 increased with virus inoculum. SARS-CoV-2 retained its infectivity in vitro in simulated human fed-gastric and fasted-intestinal fluid after two hours. Oral inoculation with the highest intranasal inoculum (10 5 PFU) caused only mild pneumonia in 67% (4/6) of the animals with no clinical symptoms. The lung histopathology and viral load were significantly lower than those infected by the lowest intranasal inoculum (100 PFU). However, 83% oral infection (10/12 hamsters) had similar level of detectable viral shedding from oral swabs and faeces as intranasally infected hamsters. Our findings indicated oral acquisition of SARS-CoV-2 can establish asymptomatic respiratory infection with less efficiency.
Subject(s)
Pneumonia , Severe Acute Respiratory SyndromeABSTRACT
Objective: Currently available COVID-19 antibody tests using enzyme immunoassay (EIA) or immunochromatographic assay have variable sensitivity and specificity. Here, we developed and evaluated a novel microsphere-based antibody assay (MBA) for the detection of immunoglobulin G (IgG) against SARS-CoV-2 nucleoprotein (NP) and spike protein receptor binding domain (RBD). Method: We developed a microsphere-based assay (MBA) to determine the levels of IgG against SARS-CoV-2 NP and spike RBD. The seropositive cut-off mean fluorescent intensity (MFI) was set using a cohort of 294 anonymous serum specimens collected in 2018. The specificity was assessed using serum specimens collected from organ donors or influenza patients before 2020. Seropositive rate was determined among patients with COVID-19. Time-to-seropositivity and signal-to-cutoff (S/CO) ratio were compared between MBA and EIA. Results: MBA had a specificity of 100% (93/93; 95% confidence interval [CI], 96-100%) for anti-NP IgG and 98.9% (92/93; 95% CI 94.2-100%) for anti-RBD IgG. The MBA seropositive rate for convalescent serum specimens of COVID-19 patients were 89.8% (35/39) for anti-NP IgG and 79.5% (31/39) for anti-RBD IgG. The time-to-seropositivity was shorter with MBA than that of EIA. When compared with EIA, MBA could better differentiate between COVID-19 patients and negative controls with significantly higher S/CO ratio for COVID-19 patients and lower S/CO ratio with negative controls. MBA also had fewer specimens in the equivocal range (S/CO 0.9-1.1) than EIA. Conclusion: MBA is robust and simple, and is suitable for clinical microbiology laboratory for the accurate determination of anti-SARS-CoV-2 antibody for retrospective diagnosis, serosurveillance, and vaccine trials.