SARS-CoV-2 reinfection after previous infection and vaccine breakthrough infection through the second wave of pandemic in India: An observational study

BACKGROUND: There are sparse longitudinal data on SARS-CoV-2 infection after previous infection and after partial or full vaccination. METHODS: This study of a cohort of healthcare workers used Kaplan-Meier analysis with appropriate definition of events and censoring and used Cox models to assess outcomes, with data cut-off on June 18, 2021. RESULTS: A total of 1806 individuals with median age of 32 (18-64) years, 1483 (82.1%) with at least one vaccine dose, 1085 (60.1%) with 2 vaccine doses, 408 (22.6%) with at least one episode of SARS-CoV-2 infection, and 6 (1.47%) with 2 episodes of infection were included in the analysis. At median follow-up of 38.4 weeks after first SARS-CoV-2 infection (n=408), the 52-week probability of reinfection was 2.2% (95% CI, 1.0-4.91%); and at median follow-up of 13.3 weeks after second dose, the 16-week probability of breakthrough infection was 5.6% (95% CI, 4.33-7.23%), which was significantly higher among those without previous SARS-CoV-2 infection versus with previous infection (6.4% vs 1.8%, p=0.016, adjusted Cox HR=3.49, 95% CI, 1.09-11.20, p=0.036) and females versus males (7.9% vs 3.8%, p=0.007, adjusted Cox HR=2.06, 95% CI 1.19-3.56, p=0.01). CONCLUSIONS: There was low probability of reinfection after previous SARS-CoV-2 infection and higher vaccine breakthrough infections among females and those without previous infection.