Seroprevalence of SARS-CoV-2 infection in the Colombo Municipality region, Sri Lanka (preprint)

Background As the Municipality Council area in Colombo (CMC) experienced the highest number of cases until end of January 2021, in Sri Lanka, we carried out a serosurvey prior to initiation of the vaccination program to understand the extent of the SARS-CoV-2 outbreak. Methods SARS-CoV-2 seropositivity was determined in 2547 individuals between the ages of 10 to 86 years, by the Wantai total antibody ELISA. We also compared to seroprevalence using the haemagglutination test (HAT) to evaluate its usefulness in carrying out serosurveys. Results The overall seropositivity rate was 24.46%, while seropositivity by HAT was 18.9%. Although the SARS-CoV-2 infection detection rates by PCR were highest in the population between the ages of 20 to 60 years of age, the seropositivity rates were equal among all age groups. The seropositivity rate was highest in the 10 to 20 age group (34.03%), whereas the PCR positivity rates was 9.8%. Differences in the PCR positivity rates and seropositivity rates were also seen in 60- to 70-year-olds (8.9% vs 30.4%) and in individuals >70 year (4.1% vs 1.2%). The seropositivity rates of the females was 29.7% (290/976), which was significantly higher (p<0.002) than in males 21.2% (333/1571). Conclusions A high seroprevalence rate (24.5%) was seen in all age groups in the CMC suggesting that a high level of transmission was seen during this area. The PCR positivity rates, appear to underestimate the true extent of the outbreak and the age groups which were infected.

Antibody and T-cell responses to a single dose of the AZD1222/Covishield vaccine in previously SARS-CoV-2 infected and naive health care workers in Sri Lanka (preprint)

BackgroundIn order to determine the immunogenicity of a single dose of the AZD1222/Covishield vaccine in a real-world situation, we assessed the immunogenicity, in a large cohort of health care workers in Sri Lanka. MethodsSARS-CoV-2 antibodies was carried out in 607 naive and 26 previously infected health care workers (HCWs) 28 to 32 days following a single dose of the vaccine. Haemagglutination test (HAT) for antibodies to the receptor binding domain (RBD) of the wild type virus, B.1.1.7, B.1.351 and the surrogate neutralization assay (sVNT) was carried out in 69 naive and 26 previously infected individuals. Spike protein (pools S1 and S2) specific T cell responses were measured by ex vivo ELISpot IFN{gamma} assays in 76 individuals. Results92.9% of previously naive HCWs seroconverted to a single dose of the vaccine, irrespective of age and gender; and ACE2 blocking antibodies were detected in 67/69 (97.1%) previously naive vaccine recipients. Although high levels of antibodies were found to the RBD of the wild type virus, the titres for B.1.1.7 and B.1.351 were lower in previously naive HCWs. Ex vivo T cell responses were observed to S1 in 63.9% HCWs and S2 in 31.9%. The ACE2 blocking titres measured by the sVNT significantly increased (p<0.0001) from a median of 54.1 to 97.9 % of inhibition, in previously infected HCWs and antibodies to the RBD for the variants B.1.1.7 and B.1.351 also significantly increased. Discussiona single dose of the AZD1222/Covishield vaccine was shown to be highly immunogenic in previously naive individuals inducing antibody levels greater than following natural infection. In infected individuals, a single dose induced very high levels of ACE2 blocking antibodies and antibodies to RBDs of SARS-CoV-2 variants of concern. FundingWe are grateful to the World Health Organization, UK Medical Research Council and the Foreign and Commonwealth Office.