Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. The incidence density of SARS-CoV-2 reinfection among a cohort of health care workers in New Delhi, India was 7.3 per 100 person-years.

2. The inactivated vaccine BBV152 offered a high protective effect of 86% in fully vaccinated individuals against reinfection, further highlighting the evidence to fully vaccinate with appropriate doses to prevent reinfection with COVID-19.

Evidence Rating Level: 2 (Good)

Study Rundown:

Between March to June 2021, the B.1.617.2 (Delta) variant of SARS-CoV-2 caused a surge of COVID-19 infection in New Delhi, India, affecting health care workers (HCWs) with different vaccination doses. This cohort study evaluated the incidence density of reinfection among HCWs and estimated the effectiveness of the inactivated whole virion vaccine BBV152 against reinfection. HCWs were categorized as fully vaccinated (2 doses and ≥15 days after second dose), partially vaccinated (1 dose or 2 doses with <15 days after second dose), or unvaccinated. The main outcome was the incidence density of COVID-19 reinfection per 100 person years, where hazard ratios (HRs) were estimated using a Cox proportional hazards. Among 4978 HCWs diagnosed with COVID-19, the incidence density of reinfection was 7.26 per 100 person years with most cases occurring after a long follow-up period during the Delta variant surge in COVID-19 cases. Among fully vaccinated HCWs, the estimated effectiveness of the BBV152 vaccine was 86% against reinfection, where partial vaccination was not associated with reduced risk of reinfection. These results provide further evidence to fully vaccinate with the recommended doses, even among individuals previously infected with COVID-19. A limitation of this study was that genomic sequencing, a required assay for confirmation of reinfection in virological studies, was only performed in a minority of cases as this was logistically impractical. Thus, most cases should be considered possible reinfections owing to a degree of confounding and statistical imprecision.

In-Depth [retrospective cohort]:

This cohort study included 4978 HCWs (mean age [SD], 36.6 [10.3] years; 55.0% male) diagnosed with COVID-19 at a tertiary care center in New Delhi, India between March 2020 and June 2021. The vaccination status of HCWs varied across 0, 1, or 2 doses of the BBV152 vaccine. Overall, 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), where 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 to unvaccinated HCWs. Specifically, reinfection was observed in 60 of 472 (12.7%) unvaccinated individuals (incidence density, 18.05 per 100 person-years; 95%CI, 14.02-23.25), 39 of 356 (11.0%) 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. Partial vaccination was not associated with reduced risk of reinfection. Thus, among fully vaccinated HCWs, the estimated effectiveness of BBV152 was 86% against reinfection (95%CI, 77%-92%), 87% for symptomatic reinfection (95%CI, 76%-93%); and 84% for asymptomatic reinfection (95%CI, 47%-95%).

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