High Post-infection Protection after COVID-19 Among Healthcare Workers: A Population-Level Observational Study Regarding SARS-CoV-2 Reinfection, Reactivation, and Re-positivity and its Severity

Abstract

Abstract Introduction: Even though over a year has passed since the coronavirus 2019 (COVID-19) outbreak, our information regarding certain aspects of the disease, such as post-infection immunity is still very limited. This study aimed to evaluate post-infection protection and COVID-19 features among healthcare workers (HCWs), during three subsequent surges.Method: The study population consisted of all HCWs in either public or private hospitals in Fars province, Southern Iran from 20 April 2020 up to 20th February 2021. We calculated the rate of infection as the number of individuals with positive PCR tests divided by the cumulative number of person-days at risk. Poisson regression was utilized to calculate the adjusted rate ratio and estimated protection. Results: During the study period, a total of 30,546 PCR tests were performed among HCWs, of which 13,749 HCWs were positive. Among a total of 141 diagnosed cases who experienced a second episode of COVID-19, 44 (31.2%) cases of reactivation and relapse, and 97 (68.8% of infected and 1.81% of total HCWs) cases of reinfection was observed. The daily rate of infection was 4.72 for previously infected HCWs, while 2.20 for HCWs without previous infection. The estimated protection against repeat infection after a previous SARS-CoV-2 infection was 94.8% (95% CI: 93.6-95.7).Conclusion: Re-positivity, relapse, and reinfection of SARS-CoV-2 are quite rare in the population of HCWs. Also, after a first episode of infection, estimated protection of 94.8% was achieved against repeat infections.