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.

Risk of SARS-CoV-2 reinfection: a systematic review and meta-analysis

“…As the data related to SARS-CoV-2 reinfection becomes more available, sub-analyses could be explored to examine the rates of reinfection by a variety of covariates, such as age, sex, comorbidities and history of vaccination. The results from this meta-analysis may serve as a comparison to future research on the risk of reinfection of Omicron and new emerging variants among the widely vaccinated population 61 , 62 .…”

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.…”

Estimation of Near-kink Reproduction Numbers During the Emergent Variants of the COVID-19 Pandemic: Log-quadratic and Forward-imputation Approach

“…Currently, COVID- 19 has not yet been globally eliminated and experienced multiple waves of variants [31][32][33][34][35][36][37][38][39]. The proposed method partially incorporated the uncertainty of imputed cases, the heterogeneity of transmission dynamics, and the uncertainty of the growth rate estimates through the channels of sliding windows, data distribution, generation intervals, and reporting rates.…”

“…Studies found that non-compulsory measures reduced population mobility using mobile-phone data in Tokyo [8,34]. The survey conducted in Bulgaria implied that prior records of infections could confer certain levels of immunity protection, implicitly yielding an impact on the trajectory of later reinfection [35]. Second, other exterior driving factors may be playing roles as well, such as policies, environmental scenarios, urban space features, and potential interactions [36].…”