Epidemiological assessment of SARS-COV-2 reinfection

Objectives: SARS-CoV-2 vaccination has shown reduced infection severity; however, the reinfection frequency amongst unvaccinated, partially vaccinated and fully vaccinated remains unclear. This study aims to elucidate the rates and associated factors for such occurrences.

Methods: This retrospective epidemiological report included 1362 COVID-19 reinfection cases in Bahrain between April 2020 and July 2021. We analysed differences in disease severity and reinfection characteristics between various vaccination statuses; fully vaccinated, interrupted vaccination, one vaccination dose, post-reinfection vaccination and unvaccinated.

Results: Reinfection cases increased from zero cases per month in April - June 2020 to a sharp peak of 579 reinfection cases in May 2021. Males constituted a significantly larger proportion of reinfections (60.3%, p<0.0001). Reinfection episodes were highest amongst the 30-39 years of age (29.7%). The least reinfection episodes occurred at 3-6 months after the first infection (20.6%) and most occurred ≥9 months after initial infection (46.4%). Most individuals were asymptomatic during both episodes (35.7%), Reinfection disease severity was mild, with vaccinated patients less likely to have symptomatic reinfection (OR 0·71, p=0·004). Only 6.6% reinfection cases required hospitalization. One death was recorded, corresponding to unvaccinated group.

Conclusion: Vaccine-induced immunity and prior infection with or without vaccination were effective in reducing reinfection disease severity.