S2. proportion of reinfections caused by Gamma during the second wave in Manaus and the safety conferred by earlier infection, we recognized anti-SARS-CoV-2 antibody improving in repeat blood donors like a mean to Sulfacarbamide 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 Sulfacarbamide reinfection-induced improving. Donors were required to have three or more donations, being at least one during each epidemic wave. We propose a rigid serological definition of reinfection (reactivity improving following waning just like a V-shaped curve in both assays or three spaced boostings), Sulfacarbamide probable (two separate improving events) and possible (reinfection recognized by only one assay) reinfections. The serial samples were used to divide donors into six organizations defined based on the inferred sequence of illness and reinfection with non-Gamma and Gamma variants. Results From 3655 repeat blood donors, 238 met all inclusion criteria, and 223 experienced enough residual sample volume to perform both serological assays. We found 13.6% (95% CI 7.0C24.5%) of all presumed Gamma infections that were observed in 2021 were reinfections. If we also include instances of probable or possible reinfections, these percentages increase respectively to 22.7% (95% CI 14.3C34.2%) and 39.3% (95% CI 29.5C50.0%). Earlier illness conferred a safety against reinfection of 85.3% (95% CI 71.3C92.7%), decreasing to Sulfacarbamide respectively 72.5% (95% CI 54.7C83.6%) and 39.5% (95% CI 14.1C57.8%) if probable and possible reinfections are included. Conclusions Reinfection by Gamma is definitely common and may play a significant part in epidemics where Gamma is definitely prevalent, highlighting the continued danger variants of concern present actually to settings previously hit by considerable epidemics. Supplementary Information The online version consists of supplementary material available at 10.1186/s12879-022-07094-y. is definitely a predefined parameter equal to 141?days and 126?days for the anti-N and anti-S assays, respectively (see Additional file 1: Appendix for an explanation on how was obtained). We hypothesize that donors following this rule have had an unobserved antibody decrease after the 1st positive sample, and seroconverted again after becoming reinfected. A minimum interval between donations is required to avoid misclassifying donors sampled during the seroconversion period as probable reinfections. Table 2 Summarized definition and size of the groups used to classify donors for each assay Donors with this group have an observed seroconversion period much longer than expected120Probable reinfection by GammaOne positive result in 2020 and a higher positive result in 2021 separated by an interval of at Rabbit Polyclonal to Collagen IX alpha2 least (seroconversion period longer than expected)797Possible reinfection by GammaClassification as Reinfection by Gamma by only one assay (reinfection recognized by one assay but not both)18Unknown (anti-S assay only)Not enough volume to retest the sample with the anti-S assay15Total.238238238 Open in a separate window The final classification was obtained by combining the groups assigned by both assays relating to Table ?Table1.1. The meanings of probable reinfections depend within the parameter days for the anti-N assay and 126?days for the Sulfacarbamide anti-S assay These rules imply that a reinfected individual may be misclassified while Illness by Gamma or Illness by non-Gamma variant if samples are not collected shortly after the first illness, underestimating the proportion of reinfections. To partially account for this.