The use of residual serum samples to perform serological surveillance of severe acute respiratory syndrome coronavirus 2 in Dili and regional areas of Timor-Leste

Background Lack of access to diagnostic testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can limit disease surveillance in remote areas. Serological surveillance can indicate the true extent and distribution of infections in such settings. Methods This study monitored SARS-CoV-2 seroprevalence in residual serum samples salvaged from laboratories at five healthcare facilities across Timor-Leste from March to October 2021. Results Seroprevalence increased from 8.3% to 87.0% during the study period. Potential immunity gaps were identified among children aged 0-15 y (who had not been eligible for vaccination) and individuals aged >60 y. Conclusions Efforts to vaccinate vulnerable individuals including older people should be maintained. Residual serum samples can be analysed to give local, contemporary information about the extent and distribution of antibodies to infections, especially SARS-CoV-2, in areas where epidemiological information is limited.