COVID-19 vaccine effectiveness among healthcare workers in Portugal: results from a hospital-based cohort study, December 2020 to November 2021

IntroductionHealthcare workers (HCW) were amongst the first prioritized for COVID-19 vaccination but data on COVID-19 vaccine effectiveness among HCW is still limited. This study aims to estimate the COVID-19 vaccine effectiveness (VE) against SARS-CoV-2 symptomatic infection among HCW from Portuguese hospitals. MethodsIn this prospective cohort study, we analysed data from HCW (all professional categories) from two central hospitals in the Lisbon and Tagus Valley and Centre regions of mainland Portugal between December 2020 and November 2021. VE against symptomatic SARS-CoV-2 infection was estimated as one minus the confounder adjusted hazard ratios by Cox models considering age group, sex, presence of chronic disease and occupational exposure to patients diagnosed with COVID-19 as adjustment variables. ResultsDuring the 11 months of follow up, the 2213 HCW contributed a total of 1950 person-years at risk and 171 SARS-CoV-2 events occurred. The COVID-19 incidence rate for unvaccinated HCW was 348.7 per 1000 person-years while for fully vaccinated HCW was 43.0 per 1000 person-years. We observed a VE against symptomatic SARS-CoV-2 infection of 73.9% (95% CI: 26.2-90.8%) for complete vaccination status. ConclusionThis cohort study found a high COVID-19 VE against symptomatic SARS-CoV-2 infection in Portuguese HCW, which is in concordance with previous studies from other countries. Monitoring of VE in this HCW cohort continues during the winter 2021/2022 to evaluate potential VE decay and booster vaccine effect.