The magnitude and cross reactivity of SARS-CoV-2 specific antibody responses in Sri Lankan children and association with the nutritional status

Background In order to determine if undernutrition affects the presence, breadth and magnitude of antibodies to SARS-CoV-2 and variants, we studied SARS-CoV-2 specific antibody responses in a large island wide serosurvey in children in Sri Lanka. Methods Using the WHO UNITY protocol, we recruited 5207 children, aged 10 to 20 years, and assessed anthropometric measures, seropositive rates, ACE2 blocking antibodies and antibodies to omicron variants, in vaccinated and unvaccinated children. Results 3111/3119 (99.7%) vaccinated and 2008/2088 (96.2%) of unvaccinated children were seropositive for SARS-CoV-2, although the detection of ACE2 blocking antibodies were significantly higher in vaccinated children (2984/3111, 95.9%) compared to unvaccinated (1346/2008, 67.0%). 1057 (22.1%) had a BMI < 3rd centile for age, and therefore were classified as underweight. Unvaccinated children, with < 3rd BMI centile had significantly lower ACE2 blocking antibodies than other groups. There were no differences in the antibody titres to XBB.1.5 or BA.2.75 based on the BMI category. Conclusions The high seropositivity rates, with high antibody titres to SARS-CoV-2 variants in unvaccinated children indicates possible multiple infections with SARS-CoV-2. The implications of lower antibody levels in underweight children should be further investigated.