LAUSR

Background : Serosurveillance can be used to investigate the extent and distribution of immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) within a population. Characterisation of humoral immune responses gives insight into whether immunity is infection- or vaccine-derived. Methods : A longitudinal study of healthcare workers (HCWs) in Dili, Timor-Leste was conducted during vaccine roll-out (ChAdOx1) and a concurrent SARS-CoV-2 outbreak. Results : Three-hundred-and-twenty-four HCWs were included at baseline (April-May 2021). Thirty-two (9.9%) were anti-Nucleocapsid protein IgG (anti-N), indicating significant subclinical infection among HCWs early in the local outbreak. One-hundred-and-fifty-seven (48.5%) participants were followed-up (July-September 2021), by which time there had been high uptake of vaccination (91.7%) and 86.0% were anti-S seropositive. Acquisition of anti-N antibodies was observed in partially vaccinated HCWs (30/76, 39.5%), indicating some post-dose 1 infections. Discussion : Serosurveillance of HCWs may provide early-warning of SARS-CoV-2 outbreaks and should be considered in non-endemic settings, particularly where there is limited availability/uptake of testing for acute infection. Characterisation of humoral immune responses may be used to assess vaccine impact as well as coverage. Such studies should be considered in national and international efforts to investigate and mitigate against future emerging pathogens.