A seroprevalence study of SARS-CoV-2 and seasonal coronaviruses after the first SARS-CoV-2 circulation in New Caledonia, Pacific region

Objective The aim of this study was to determine the seroprevalence of IgG antibodies targeting SARS-CoV-2 and other human coronaviruses after the first circulation of SARS-CoV-2 in New Caledonia, Pacific region. Methodology Blood samples were collected to detect the presence of SARS-CoV-2 IgG antibodies. Sampling took place between July 2021 and July 2022 but was interrupted following the first circulation of SARS-CoV-2 (September 2021-March 2022) in New Caledonia. Data on ethnicity, age, gender, main residence and anteriority of COVID-19 and vaccination were collected and analyzed. Findings A total of 747 participants, representative of New Caledonia's adult population, were included in the study. We found that 81% of the population had antibody responses to SARS-CoV-2 at the end of July 2022. The vaccination rate was 75%, while infections had affected 40% of the population. Individuals aged >45 were significantly more vaccinated than those aged 18-44 (80% (95% CI 74-84%). Oceanians were the most infected (50% (95% CI 42-57%). Conclusions In New Caledonia, we show a high immunity rate (81%) following the first waves of SARS-CoV-2 circulation and the vaccination campaign. The analyses showed spatial heterogeneities in the infection rate across the territory and revealed that Oceanians were the most infected. Our study also highlighted high exposure of New Caledonia's population to other human coronaviruses.