SARS-CoV-2 reinfections during the first three major COVID-19 waves in Bulgaria

Abstract

Background: The COVID-19 pandemic has had a devastating impact on the world over the past two years (2020-2021). One of the key questions about its future trajectory is the protection from subsequent infections and disease conferred by a previous infection, as the SARS-CoV-2 virus belongs to the coronaviruses, a group of viruses the members of which are known for their ability to reinfect convalescent individuals. Bulgaria, with high rates of previous infections combined with low vaccination rates and an elderly population, presents a somewhat unique context to study this question. Methods: We use detailed governmental data on registered COVID-19 cases to evaluate the incidence and outcomes of COVID-19 reinfections in Bulgaria in the period between March 2020 and early December 2021. Results: For the period analyzed, a total of 4,106 cases of individuals infected more than once were observed, including 31 cases of three infections and one of four infections. The number of reinfections increased dramatically during the Delta variant-driven wave of the pandemic towards the end of 2021. We observe a moderate reduction of severe outcomes (hospitalization and death) in reinfections relative to primary infections, and a more substantial reduction of severe outcomes in breakthrough infections in vaccinated individuals. Conclusions: In the available datasets from Bulgaria, prior infection appears to provide some protection from severe outcomes, but to a lower degree than the reduction in severity of breakthrough infections in the vaccinated compared to primary infections in the unvaccinated.

The impact and progression of the COVID-19 pandemic in Bulgaria in its first two years

“…First, a majority of the population must have been infected by that point (other-wise the IFR in Bulgaria would have to exceed 2%, which is unlikely), although how many exactly have been infected is not possible to say in the absence of an anti-nucleocapside serosurvey (and even then, seroreversion would probaly bias estimates downwards). Second, reinfections became an increasingly common phenomenon, first with the arrival of the Delta variant 38 , and especially after the appearance of Omicron. Third, the virulence of SARS-CoV-2 prior to Omicron was increasing, with the Alpha variant being more severe than the WT and the Delta variant being even more severe than Alpha; meanwhile the IFR estimates from 2020 and early 2021 were based on the WT virus.…”

SARS-CoV-2 Reinfection is Preceded by Unique Biomarkers and Related to Initial Infection Timing and Severity: an N3C RECOVER EHR-Based Cohort Study

“…15,16 One study found that the reduced risk of hospitalization following reinfection persisted when disaggregated by age. 17 No study has clearly disaggregated by severity of hospitalization, such as considering the distinction between an emergency department (ED) visit, an inpatient hospitalization, and an inpatient hospitalization requiring intensive care. In this work, we aim to assess the association between the severity of initial infection and severity of first reinfection to contribute more granular findings disaggregated by severity of hospitalization.…”