Abstract
A surge of COVID-19 occurred from March to June 2021, in New Delhi, India, linked to the B.1.617.2 (Delta) variant of SARS-CoV-2. COVID-19 vaccines were rolled out for health care workers (HCWs) starting in January 2021. To assess the incidence density of reinfection among a cohort of HCWs and estimate the effectiveness of the inactivated whole virion vaccine BBV152 against reinfection. This was a retrospective cohort study among HCWs working at a tertiary care center in New Delhi, India. Vaccination with 0, 1, or 2 doses of BBV152. The HCWs were categorized as fully vaccinated (with 2 doses and ≥15 days after the second dose), partially vaccinated (with 1 dose or 2 doses with <15 days after the second dose), or unvaccinated. The incidence density of COVID-19 reinfection per 100 person-years was computed, and events from March 3, 2020, to June 18, 2021, were included for analysis. Unadjusted and adjusted hazard ratios (HRs) were estimated using a Cox proportional hazards model. Estimated vaccine effectiveness (1 - adjusted HR) was reported. Among 15 244 HCWs who participated in the study, 4978 (32.7%) were diagnosed with COVID-19. The mean (SD) age was 36.6 (10.3) years, and 55.0% were male. The reinfection incidence density was 7.26 (95% CI: 6.09-8.66) per 100 person-years (124 HCWs [2.5%], total person follow-up period of 1696 person-years as time at risk). Fully vaccinated HCWs had lower risk of reinfection (HR, 0.14 [95% CI, 0.08-0.23]), symptomatic reinfection (HR, 0.13 [95% CI, 0.07-0.24]), and asymptomatic reinfection (HR, 0.16 [95% CI, 0.05-0.53]) compared with unvaccinated HCWs. Accordingly, among the 3 vaccine categories, reinfection was observed in 60 of 472 (12.7%) of unvaccinated (incidence density, 18.05 per 100 person-years; 95% CI, 14.02-23.25), 39 of 356 (11.0%) of partially vaccinated (incidence density 15.62 per 100 person-years; 95% CI, 11.42-21.38), and 17 of 1089 (1.6%) fully vaccinated (incidence density 2.18 per 100 person-years; 95% CI, 1.35-3.51) HCWs. The estimated effectiveness of BBV152 against reinfection was 86% (95% CI, 77%-92%); symptomatic reinfection, 87% (95% CI, 76%-93%); and asymptomatic reinfection, 84% (95% CI, 47%-95%) among fully vaccinated HCWs. Partial vaccination was not associated with reduced risk of reinfection. These findings suggest that BBV152 was associated with protection against both symptomatic and asymptomatic reinfection in HCWs after a complete vaccination schedule, when the predominant circulating variant was B.1.617.2.
Highlights
The global COVID-19 pandemic has been ongoing since March 2020.1 As of November 23, 2021, more than 257 million COVID-19 cases and 5.15 million fatalities had been reported
Among 15 244 health care worker (HCW) who participated in the study, 4978 (32.7%) were diagnosed with COVID-19
SARS-CoV-2 Reinfection Rates Among Health Care Workers After Vaccination With BBV152. These findings suggest that BBV152 was associated with protection against both symptomatic and asymptomatic reinfection in HCWs after a complete vaccination schedule, when the predominant circulating variant was B.1.617.2
Summary
The global COVID-19 pandemic has been ongoing since March 2020.1 As of November 23, 2021, more than 257 million COVID-19 cases and 5.15 million fatalities had been reported. The second wave recorded a greater magnitude of cases and fatalities, owing to high transmissibility and virulence of the B.1.617.2 (Delta) variant.[3]. Health care workers (HCWs) are at increased risk for SARS-CoV-2 infection as a result of potential occupational exposure.[4,5] Cases of reinfection among HCWs have been reported since June 2020.6,7 Multiple reasons have been posited for reinfection among HCWs, including persistent occupational exposure; waning natural immunity over time; insufficient seroconversion during a first, milder episode; pandemic fatigue with laxity in personal protection and/or COVID-appropriate behavior; and, possibly, immune escape due to new variants.[8] Emergency use authorization was awarded to inactivated whole virion vaccine BBV152 (Bharat Biotech Ltd), which is produced in India; this was used in the initial launch of a vaccination program against COVID-19 for HCWs that began on January 16, 2021.9 This vaccine requires refrigeration storage at 2 to 8 °C and is available in multidose vials
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