Risk of work-related Corona virus disease 2019 (COVID-19) among healthcare workers of the Royal Thai Army before and after COVID 19 vaccination between 2020-2021
Abstract:
COVID-19 is an infectious respiratory disease spreading extensively worldwide and causing a wide range of symptoms, extending from mild to fatal. Previously, research showed that healthcare workers (HCWs) caring specifically for COVID-19 or general patients are at a higher risk of contracting the COVID-19 than health management and support workers. However, existing studies are mostly cross-sectional, thereby limiting causal inference. This retrospective cohort study aimed to determine the incidence rate of COVID-19 infection among 3 groups of HCWs (i.e. those caring for COVID-19 patients, those caring for general patients, and those not caring for patients) of the Royal Thai Army during the pandemic years 2020-2021. Data relating to personal demographics, job characteristics, and histories of COVID-19 infections and vaccinations during the study period were collected from the relevant documents of 27 hospitals under the jurisdiction of the Royal Thai Army and covered 9,576 healthcare workers in total. The result showed that the incidence rate (95% confidence interval: CI) of COVID-19 infection among HCWs caring for COVID-19 patients, those caring for general patients, and those not caring for patients were 1,431.53 (970.90, 1,755.65), 1,306.34 (970.90, 1,755.65), and 1,699.81 (1,394.30, 2,069.55) persons per 100,000 person-years respectively. Group comparison via the relative risk (RR) showed that the infection risk among these HCWs did not differ significantly, with the adjusted RR (95%CI) of 0.86 (0.51, 1.45) and 0.89 (0.50, 1.61) respectively for the first and second comparing to the third HCW groups. Further analyses by categorizing into pre- and post-vaccination periods did not materially change this finding, although the infection incidence enormously increased during the latter period, probably coincident with the pre- and post-delta variant periods. In conclusion, our results implied that community-acquired COVID-19 infection is as important, if not more, as work-related infection for the HCWs. Prevention the HCWs against this and similar infections in future epidemics should therefore focus on both the infectious sources from community and work.