Background: COVID-19 has become a global pandemic, leading to the development of various vaccines to protect against infection. Sinovac-CoronaVac COVID-19 vaccine, an inactivated virus vaccine developed by Sinovac Biotech, has been approved for use. However, limited information is available regarding the immunity level provided by Sinovac-CoronaVac.

Objective: To determine the level of anti-SARS-CoV-2 spike protein antibodies 28 and 90 days after the administration of the second dose of CoronaVac.

Materials and Methods: A descriptive study was conducted, involving 132 healthcare personnel. The antibody levels were measured using the Roche Elecsys anti-SARS-CoV-2 spike protein immunoassay, both at 28 and 90 days after the second dose of CoronaVac.

Results: The majority of participants were female registered nurses. The geometric mean antibody levels on day 28 and 90 were 138.1±2.2 and 66.9±0.3, respectively. By day 90, the antibody levels had declined to 45.3% compared to day 28. Nearly all participants had immunity levels on day 90 lower than those resulting from natural infection.

Conclusion: The present study findings indicated that the immunity level, as measured by anti-SARS-CoV-2 spike protein antibodies, declined below the level observed with natural infection by day 90. Additional vaccine doses are suggested for healthcare personnel to provide rapid protection of the infection.

Keywords: Antibody level; COVID-19; Health care personnel; Immunity

DOI: 10.35755/jmedassocthai.2023.07.13819

Received 20 March 2023 | Revised 31 May 2023 | Accepted 2 June 2023