SARS-CoV-2 seropositivity amongst healthcare workers in South Africa during the Omicron wave: natural infection versus vaccination.

Aims: Concerns over population-level immunity have been heightened with each successive wave of COVID-19, prompting questions about whether it is primarily derived from vaccination efforts or from previous natural infections with the virus. We wished to determine the seroprevalence of SARS-CoV-2 antibodies among healthcare workers (HCWs) in Pretoria (Tshwane), South Africa, and to establish whether they were derived from vaccination or natural infection.

Methods: Serum samples were collected from HCWs during the fourth wave of COVID-19 between 1 December 2021 and 13 March 2022. The samples were tested using the Abbott SARS-CoV-2 Spike IgG (S-IgG), IgM (S-IgM) and the SARS-CoV-2 Nucleocapsid IgG (NC-IgG) kits.

Results: Of the 221 participants, 76% (n=168) were women and 24% (n=53) were men. A total of 96.4% (n=213) of the participants were vaccinated. Natural infection-derived antibodies were detected in 23% (n=51) of participants, and vaccine-derived antibodies in 74% (n=164) of the HCWs.

Conclusions: Even after three waves of COVID-19, HCWs derived most of their detectable antibodies from vaccination. Vaccination remains an essential tool to protect HCWs and patients from SARS-CoV-2 infection.