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

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

Effects of BDNF polymorphism and physical activity on episodic memory in the elderly: a cross sectional study

International audienceBackground:The brain-derived neurotrophic factor (BDNF) concentration is highest in the hippocampus comparedwith that in other brain structures and affects episodic memory, a cognitive function that is impaired in olderadults. According to the neurotrophic hypothesis, BDNF released during physical activity enhances brain plasticity andconsequently brain health. However, even if the physical activity level is involved in the secretion of neurotrophin, thisprotein is also under the control of a specific gene. The aim of the present study was to examine the effect of theinteraction between physical activity and BDNF Val66Met(rs6265), a genetic polymorphism, on episodic memory.Methods:Two hundred and five volunteers aged 55 and older with a Mini Mental State Examination score≥24participated in this study. Four groups of participants were established according to their physical activity level andpolymorphism BDNF profile (Active Val homozygous, Inactive Val homozygous, Active Met carriers, Inactive Met carriers).Episodic memory was evaluated based on the delayed recall of the Logical Memory test of the MEM III battery.Results:As expected, the physical activity level interacted with BDNF polymorphism to affect episodic memoryperformance (p< .05). The active Val homozygous participants significantly outperformed the active Met carriers andinactive Val homozygous participants.Conclusion:This study clearly demonstrates an interaction between physical activity andBDNF Val66Metpolymorphismthat affects episodic memory in the elderly and confirms that physical activity contributes to the neurotrophic mechanismimplicated in cognitive health. The interaction shows that only participants with Val/Val polymorphism benefited fromphysical activit