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

Abstract

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.

Keywords: COVID-19 pandemic; Healthcare workers; Nucleocapsid antibody; SARS-CoV-2 antibodies; Seroprevalence; Spike protein antibody.

Figure 1

The timeline of the study. T1 to T5 reflects the five time points when sampling was done for the seroprevalence study. The first coronavirus disease 2019 (COVID-19) case was reported in India on 27^th January 2020. The index case of COVID-19 was reported in our institution on 28^th March 2020 while the first confirmed COVID-19 infection in a healthcare worker (HCW) was reported on 5^th July 2020. The period T1 to T3 denotes the first wave of the pandemic during which time vaccine was not available. Vaccination for COVID-19 started in India for HCWs on January 16^th, 2021. T4 and T5 denote the period when vaccination was rolled out in a phased manner and also reflects the period when the second wave of the pandemic occurred in India. COVID-19: Coronavirus disease 2019; HCW: Healthcare worker.

Figure 2

The seropositivity outcomes among healthcare workers working in high-risk and low-risk areas in our hospital. High-risk areas refer to those working in the emergency department and/or the medical intensive care unit; low-risk (LR) areas refer to those working in paraclinical areas such as anatomy, physiology, biochemistry, or community medicine. Although healthcare workers (HCWs) in LR areas were not supposed to work in coronavirus disease 2019 (COVID-19) wards, they were requested to work in COVID-19 wards for short periods during the peak of the 2^nd wave when the health system was overwhelmed with many patients. Clinical infection occurred among 120 of the 366 HCWs who were working in high-risk (HR) areas. Sero-study was done in 143 of the 366 HCWs in HR areas. At the end of the study 66.4% were positive for nucleocapsid antibodies and 97.9% were positive for spike antibodies. Among HCWs working in LR areas, 22 of the 82 HCWs developed clinical infection. At the end of the study 59.3% were positive for nucleocapsid antibodies and 94.9% were positive for spike antibodies. ¹Only 202 HCWs who gave at least one sample for antibodies during the second wave (T4 or T5) and at least one baseline or T2 or T3 sample, and those who were unvaccinated or were vaccinated with COVISHIELD™ were included for the analysis on sero-study outcome. HCWs who were vaccinated with COVAXIN^® were excluded from the sero-study analysis as it triggers nucleocapsid and spike antibodies and mimics infection. Clinical outcomes were followed up for all 448 HCWs.