Reinfection by the SARS-CoV-2 Gamma variant in blood donors in Manaus, Brazil

Abstract

Background The city of Manaus, north Brazil, was stricken by a second epidemic wave of SARS-CoV-2 despite high seroprevalence estimates, coinciding with the emergence of the Gamma (P.1) variant. Reinfections were postulated as a partial explanation for the second surge. However, accurate calculation of reinfection rates is difficult when stringent criteria as two time-separated RT-PCR tests and/or genome sequencing are required. To estimate the proportion of reinfections caused by Gamma during the second wave in Manaus and the protection conferred by previous infection, we identified anti-SARS-CoV-2 antibody boosting in repeat blood donors as a mean to infer reinfection. Methods We tested serial blood samples from unvaccinated repeat blood donors in Manaus for the presence of anti-SARS-CoV-2 IgG antibodies using two assays that display waning in early convalescence, enabling the detection of reinfection-induced boosting. Donors were required to have three or more donations, being at least one during each epidemic wave. We propose a strict serological definition of reinfection (reactivity boosting following waning like a V-shaped curve in both assays or three spaced boostings), probable (two separate boosting events) and possible (reinfection detected by only one assay) reinfections. The serial samples were used to divide donors into six groups defined based on the inferred sequence of infection and reinfection with non-Gamma and Gamma variants. Results From 3655 repeat blood donors, 238 met all inclusion criteria, and 223 had enough residual sample volume to perform both serological assays. We found 13.6% (95% CI 7.0–24.5%) of all presumed Gamma infections that were observed in 2021 were reinfections. If we also include cases of probable or possible reinfections, these percentages increase respectively to 22.7% (95% CI 14.3–34.2%) and 39.3% (95% CI 29.5–50.0%). Previous infection conferred a protection against reinfection of 85.3% (95% CI 71.3–92.7%), decreasing to respectively 72.5% (95% CI 54.7–83.6%) and 39.5% (95% CI 14.1–57.8%) if probable and possible reinfections are included. Conclusions Reinfection by Gamma is common and may play a significant role in epidemics where Gamma is prevalent, highlighting the continued threat variants of concern pose even to settings previously hit by substantial epidemics.

SARS‐CoV‐2 variants and vulnerability at the global level

“… 64 Reinfection by Gamma is widespread and may play a large role in epidemics where Gamma is ubiquitous, emphasizing the ongoing hazard variations of concern pose even in situations where big epidemics have occurred. 69 Although the clinical significance and transmissibility of reinfections were not investigated, the projected reinfection rates imply that the Gamma variation may cause a greater infection risk than earlier non‐Gamma versions. As the majority of blood donors had asymptomatic or oligosymptomatic illnesses, the found protection against reinfection does not generalize to cohorts of exclusively hospitalized or symptomatic people.…”

“…As the majority of blood donors had asymptomatic or oligosymptomatic illnesses, the found protection against reinfection does not generalize to cohorts of exclusively hospitalized or symptomatic people. 64 , 69 , 70 …”

“…Gamma was discovered to be prevalent in adolescent ICU patients in February 2021 64 . Reinfection by gamma is widespread and may play a large role in epidemics where gamma is ubiquitous, emphasizing the ongoing hazard variations of concern pose even in situations where big epidemics have occurred 69 . Although the clinical significance and transmissibility of reinfections were not investigated, the projected reinfection rates imply that the gamma variation may cause a greater infection risk than earlier non‐gamma versions.…”

Transmission dynamics of COVID-19 pandemic with combined effects of relapse, reinfection and environmental contribution: A modeling analysis

“…Furthermore, heterogeneity and super-spreading event have also been investigated [27] , [28] . In addition, the issue of reactivation [29] , [30] , [31] , [32] , [33] , [34] , [35] , [36] , and reinfection [37] , [38] , [39] , [40] , [41] , [42] , [43] have also been studied to explore their impact on the overall transmission of SARS-CoV-2.…”

“…A relapse (which is of no or less infectiousness) observed during the first eight weeks of sickness implies that retest or isolation is unneeded [46] . Reinfection of SARS-CoV-2 is typically defined as clinical recurrence of COVID-19 followed by a positive PCR test in ( )90 days (on average) after commencement of the primary infection; it usually has reduced infectiousness compared to new infection [39] , [46] . Moreover, after a symptom-free interval and re-positive PCR outcomes, the motley of clinical recurrence of SARS-CoV-2 infection has not been researched vastly and may be rare in outpatients.…”