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

BackgroundWe investigated the seropositivity rates of Sri Lankan children in a large island wide serosurvey, to determine the magnitude and breadth of antibody responses to SARS-CoV-2 variants and the association with the vaccination and nutritional status to understand the likely impact of newer variants in Sri Lanka. MethodsUsing the WHO UNITY protocol, we recruited 5207 children, aged 10 to 20 years, representative of the 9 provinces of Sri Lanka, and assessed seropositive rates, ACE2 blocking antibodies and antibodies to BA.2.75 and XBB.1.5, in vaccinated and unvaccinated children. Anthropometric measurements were taken to determine the association between nutrition status and antibody levels. Results3111/3119 (99.7%) vaccinated and 2008/2088 (96.2%) of unvaccinated children, were seropositive for SARS-CoV-2. 2984/3111 (95.9%) of vaccinated children had ACE2 blocking antibodies above the cut-off threshold, compared to 1346/2008 (67.0%) of unvaccinated children. 27.2 % unvaccinated children had positive antibody responses to BA.2.75 and 30.7% to XBB.1.5, while 64.3% of vaccinated had a positive response to BA.2.75 and 43.1% to XBB.1.5. Vaccinated children had significantly higher titres of total antibodies, ACE2 blocking antibodies and antibodies to XBB.1.5 and BA.2.75 than unvaccinated children. However, the vaccinated had significantly higher responses to BA.2.75 (p<0.0001), than XBB.1.5. Unvaccinated children, with <3rd BMI centile had significantly lower ACE2 blocking antibodies than other groups. DiscussionThe high seropositivity rates and antibody titres to SARS-CoV-2 variants in unvaccinated children, suggests that they are likely to have been infected more than once with SARS-CoV-2. The implications of lower antibody levels in undernourished children should be further investigated.