Performance of vaccination with CoronaVac in a cohort of healthcare workers (HCW) - preliminary report

Faria, E.; Guedes, A. R.; Oliveira, M. S.; Moreira, M. V. G.; Maia, F. L.; Barboza, A. S.; Leme, M. D.; Letaif, L. S. H.; Miethke-Morais, A.; Bonfa, E.; Segurado, A. C.; Tomazini, F. M.; Santos, A. A.; Figueiredo, P.; Andrade, P. S.; Oliveira, F. M.; Eliodoro, R. H. d. A.; de Jesus, J. G.; Lazari, C. S.; Sabino, E. C.; Costa, S. F.; Pedroso de Lima, A. C.; Levin, A. S.

Background: CoronaVac, a vaccine containing inactivated SARS-CoV-2, demonstrated efficacy of 50.39% 14 days or more after the 2nd dose. The objective of this study is to report the occurrence of symptomatic COVID-19 in a cohort of HCW vaccinated with CoronaVac and to estimate its effectiveness. Methods: CoronaVac was given to HCWs in Hospital das Clinicas on 18-21 January, 2021 (epi week 3) (22,402 HCWs), and on 14-16 February, 2021 (epi week 7) (21,652 HCWs). Weekly cases of symptomatic COVID-19 were evaluated. Using the period from 2020 epi week 24 through 2021 epi week 2 (before vaccination), a Poisson regression was fit to model the HCWs with COVID-19 of the hospital, and the officially reported cases in the city of Sao Paulo. The predicted numbers of cases among HCWs for 2021 epi weeks 3-12 were then compared to the observed numbers of cases (after vaccination). Effectiveness was estimated for weeks 9-12 (2 to 5 weeks after the 2nd dose). 142 samples after vaccination were evaluated for SARS-CoV-2 variants of concern. Results: Since the 1st dose there were 380 HCW diagnosed with COVID-19. On visual analysis, the number of cases of COVID-19 in the city increased sharply in 2021. The number of cases among the HCW did not follow. The estimated effectiveness 2 and 3 weeks after 2nd dose was 50.7% and 51.8%, respectively, and increased over the next 2 weeks. 67/142 samples (47%) were variants of concern, mostly P1 (57). Conclusion: Coronavac is effective in preventing COVID-19.