Risk of COVID-19 infection among frontline healthcare workers during the COVID-19 pandemic.

Background: In the initial stages of the coronavirus disease 2019 (COVID-19) pandemic, healthcare workers (HCWs) who were immunologically naive to COVID-19, were exposed to a highly transmissible virus.

Aim: To compare infection risk among HCWs in high-risk (HR) and low-risk (LR) areas.

Methods: Data on reverse transcriptase-polymerase chain reaction confirmed clinical infection and samples for nucleocapsid, and spike protein antibodies were collected at five time-points (T1 to T5) from HCWs in the emergency department and intensive care unit (HR group) and pre-clinical and para-clinical areas (LR). For the sero-study, only participants who provided at least one baseline sample and one during the second wave (T4 or T5) were analysed. Since Covishield^TM elicits only spike protein antibodies, subclinical infection was diagnosed if asymptomatic unvaccinated and Covishield^TM vaccinated individuals tested positive for nucleocapsid antibody.

Results: Overall, by T5, clinical infection rate was similar in the HR (120/366, 32.8%) and LR (22/82, 26.8%) groups (P = 0.17). However, before vaccination (T3), more HCWs in the HR group developed COVID-19 infection (21.9% vs 8.8%, P = 0.046). In the sero-study group, clinical infection occurred in 31.5% (45/143) and 23.7% (14/59) in the HR and LR groups respectively (P = 0.23). Spike antibody was detected in 140/143 (97.9%) and 56/59 (94.9%) and nucleocapsid antibody was positive in 95/143 (66.4%) and 35/59 (59.3%) in the HR and LR groups respectively (P = 0.34). Subclinical infection rate (HR 34.9%, LR 35.6%, P = 0.37) and hospitalization rate were similar. There was no mortality.

Conclusion: Before vaccination, HCWs in HR areas had a higher risk of infection. Seroprevalence studies suggest that sub-clinical infection was not uncommon.