Impact of age on the transmission of SARS-CoV-2 in healthcare workers

Background The incidence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection was highest among older adults early in the COVID-19 pandemic; however, this pattern was later reversed with young adults showing the highest incidence. The aim of this study was to identify risk factors in healthcare workers (HCWs) associated with this evolution. Methods We conducted a survey nested within a prospective cohort study of 680 HCWs from a tertiary referral public hospital who received 2 doses of SARS-CoV-2 vaccine in January and February 2021 (VACCICO-VAO cohort). In October 2022 all participants were invited to participate in a survey. Risk factors were tested for association with COVID-19 ever, the number of COVID-19 episodes, and the time to the first episode. Results Among 350 respondents (51% response rate, 90% female, mean age 48.1 years), 323 COVID-19 episodes were diagnosed during the study period. Multivariable analysis revealed that age < 35 years vs. > 50 years (odds ratio, OR 2.12, 95% confidence interval, CI 1.27-3.51; P = 0.004) and not maintaining social distance at social events (OR: 1.82, 95% CI: 1.16-3.19; P = 0.011) were associated with a higher risk of COVID-19. Age < 35 years (hazard ratio, HR 1.70, 95% CI 1.14-2.54; P = 0.010), and not maintaining social distance (HR 1.34, 95% CI 1.05-1.72; P = 0.020) were also associated with the time to the first episode. Conclusions The youngest HCWs had the highest incidence rate of COVID-19, which was not explained by occupational risk factors or health conditions. The increase in nonoccupational exposure since the end of the lockdowns in summer 2020 could by a key factor. [GRAPHICS]