Incidence of and Risk Factors for SARS-CoV-2 Infection Among Vaccinated Healthcare Workers During Emergence of SARS-CoV-2 Gamma Variant in the Amazon Region, Brazil, 2021.

Abstract

The emergence of new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants poses a significant threat to public health and healthcare workers (HCWs). The SARS-CoV-2 Gamma variant emerged in Manaus, Brazil, in December 2020, leading to a large wave of infections and deaths. We conducted a prospective cohort study among HCWs at 2 hospitals in Manaus from 31 March to 31 May 2021. HCWs were followed up for 3 weeks with nasal swabs collected at baseline and weekly (total: 4 visits), regardless of symptoms, for SARS-CoV-2 testing. Blood samples were collected for SARS-CoV-2 serology at baseline. Staff collected data on symptoms, healthcare, and community exposures, and vaccination status at each visit. We evaluated coronavirus disease 2019 (COVID-19) attack rate, risk factors for disease, and differences in rates by vaccination status. We included 771 HCWs (388 and 383 per hospital). The median age was 40 years (IQR: 31-48), 600 (77.8%) were female, 449 (58.2%) were nurses, and 568 (73.6%) were fully vaccinated at enrollment. We identified 16 SARS-CoV-2 incident infections for an overall attack rate of 5.2 per 1000 HCW-weeks. Of the 16 infected HCWs, 12 were fully vaccinated (attack rate: 5.2/1000 HCW-weeks vs 5.9/1000 HCW-weeks among unvaccinated). All 12 vaccinated HCWs tested negative after 1-week follow-up, while 2 of the 3 infected unvaccinated individuals remained positive at follow-up (P < .05). The COVID-19 attack rate among this cohort of HCWs with high vaccine coverage was low. Among vaccinated HCWs who tested positive, none tested positive after 1 week, indicating more rapid viral clearance vs unvaccinated HCWs. HCW vaccination is an important measure for HCW safety and more resilient healthcare systems.