Surveillance of SARS-CoV-2 in Healthcare Workers Before and After COVID-19 Vaccination: A Cohort Study in a Primary Care Unit of Brazil

Introduction: Healthcare workers (HCWs) are at higher risk of SARS-CoV-2 infection. Viral surveillance for early detection of COVID-19 is a critical strategy to understand this population's infection dynamics and prevent transmission. The study examines SARS-CoV-2 infection and reinfection among HCWs vaccinated against COVID-19 working at a primary healthcare unit serving a disenfranchised community in Brazil.

Methods: The study was conducted in Cidade Estrutural, Federal District, Brazil, between February and October 2021. Participants were interviewed and provided samples. A prospective open cohort study was used to analyze the frequency of SARS-CoV-2 infection and reinfection, and the vaccine-induced seroconversion. Nasopharyngeal swab specimen was collected from workers presenting with flu-like symptoms and subjected to RT-qPCR. Peripheral blood samples were also collected every 30 ± 2 days for eight months, starting from the day participants received their first dose of COVID-19 vaccine, and submitted to serological testing (IgM and IgG chemiluminescence). The frequencies of infection and reinfection (RT-qPCR positive results 90 days after the infection) were calculated along with their respective confidence intervals (95% CI).

Results: Of the 128 workers, 61 (47.65%; CI: 39.19-56.25) reported probable SARS-CoV-2 infection before vaccination and 50 (39.06%; CI: 31.04-47.71) had SARS-CoV-2 infection after vaccination, confirmed by molecular test. Reinfection was identified in seven workers (7/50, 14%; CI: 6.95-26.18) based on the 90-day interval between results. The serological data from the 128 workers during the cohort indicated that 68 (53.12%; CI: 44.5-61.5) had IgG antibodies and 46 had IgM antibodies (35.93%; CI: 28.14-44.54) against SARS-CoV-2. SARS-CoV-2 infection was common in 56% of the community health workers (CHWs), 50% of registered nurses, and licensed vocational nurses (33%). Following the COVID-19 vaccination, the percentage of infections among HCWs decreased from 47.83% to 4.35%.

Conclusion: These results demonstrate that (i) approximately 40% of the workers were infected with SARS-CoV-2 in 2021 and (ii) reinfections confirmed by RT-qPCR occurred in 14% of the HCWs after vaccination. The results provide valuable insights into the circulation of SARS-CoV-2 among HCWs in a primary care unit serving a minoritized community.