Genetic polymorphisms in blood donors may contribute to donor-specific differences in the survival of red blood cells (RBCs) during cold storage and after transfusion. Genetic variability is anticipated to be high in donors with racial admixture from malaria endemic regions such as Africa and Asia. The purpose of this study was to test the hypothesis that donor genetic background, reflected by sex and self-reported ethnicity, significantly modulates RBC phenotypes in storage. High throughput hemolysis assays were developed and used to evaluate stored RBC samples from 11 115 African American, Asian, white, and Hispanic blood donors from 4 geographically diverse regions in the United States. Leukocyte-reduced RBC concentrate-derived samples were stored for 39 to 42 days (1–6°C) and then evaluated for storage, osmotic, and oxidative hemolysis. Male sex was strongly associated with increased susceptibility to all 3 hemolysis measures (P < .0001). African American background was associated with resistance to osmotic hemolysis compared with other racial groups (adjusted P < .0001). Donor race/ethnicity was also associated with extreme (>1%) levels of storage hemolysis exceeding US Food and Drug Administration regulations for transfusion (hemolysis >1% was observed in 3.51% of Asian and 2.47% of African American donors vs 1.67% of white donors). These findings highlight the impact of donor genetic traits on measures of RBC hemolysis during routine cold storage, and they support current plans for genome-wide association studies, which may help identify hereditable variants with substantive effects on RBC storage stability and possibly posttransfusion outcomes.

While progress has been made in characterizing humoral immunity to Zika virus (ZIKV) in humans, little is known regarding the corresponding T cell responses to ZIKV. Here, we investigate the kinetics and viral epitopes targeted by T cells responding to ZIKV and address the critical question of whether preexisting dengue virus (DENV) T cell immunity modulates these responses. We find that memory T cell responses elicited by prior infection with DENV or vaccination with tetravalent dengue attenuated vaccines (TDLAV) recognize ZIKV-derived peptides. This cross-reactivity is explained by the sequence similarity of the two viruses, as the ZIKV peptides recognized by DENV-elicited memory T cells are identical or highly conserved in DENV and ZIKV. DENV exposure prior to ZIKV infection also influences the timing and magnitude of the T cell response. ZIKV-reactive T cells in the acute phase of infection are detected earlier and in greater magnitude in DENV-immune patients. Conversely, the frequency of ZIKV-reactive T cells continues to rise in the convalescent phase in DENV-naive donors but declines in DENV-preexposed donors, compatible with more efficient control of ZIKV replication and/or clearance of ZIKV antigen. The quality of responses is also influenced by previous DENV exposure, and ZIKV-specific CD8 T cells from DENV-preexposed donors selectively upregulated granzyme B and PD1, unlike DENV-naive donors. Finally, we discovered that ZIKV

IMPORTANCE People who have been infected with or vaccinated against SARS-CoV-2 have reduced risk of subsequent infection, but the proportion of people in the US with SARS-CoV-2 antibodies from infection or vaccination is uncertain.OBJECTIVE To estimate trends in SARS-CoV-2 seroprevalence related to infection and vaccination in the US population. DESIGN, SETTING, AND PARTICIPANTSIn a repeated cross-sectional study conducted each month during July 2020 through May 2021, 17 blood collection organizations with blood donations from all 50 US states; Washington, DC; and Puerto Rico were organized into 66 study-specific regions, representing a catchment of 74% of the US population. For each study region, specimens from a median of approximately 2000 blood donors were selected and tested each month; a total of 1 594 363 specimens were initially selected and tested. The final date of blood donation collection was May 31, 2021. EXPOSURE Calendar time.MAIN OUTCOMES AND MEASURES Proportion of persons with detectable SARS-CoV-2 spike and nucleocapsid antibodies. Seroprevalence was weighted for demographic differences between the blood donor sample and general population. Infection-induced seroprevalence was defined as the prevalence of the population with both spike and nucleocapsid antibodies. Combined infection-and vaccination-induced seroprevalence was defined as the prevalence of the population with spike antibodies. The seroprevalence estimates were compared with cumulative COVID-19 case report incidence rates. RESULTS Among 1 443 519 specimens included, 733 052 (50.8%) were from women, 174 842 (12.1%) were from persons aged 16 to 29 years, 292 258 (20.2%) were from persons aged 65 years and older, 36 654 (2.5%) were from non-Hispanic Black persons, and 88 773 (6.1%) were from Hispanic persons. The overall infection-induced SARS-CoV-2 seroprevalence estimate increased from 3.5% (95% CI, 3.2%-3.8%) in July 2020 to 20.2% (95% CI, 19.9%-20.6%) in May 2021; the combined infection-and vaccination-induced seroprevalence estimate in May 2021 was 83.3% (95% CI, 82.9%-83.7%). By May 2021, 2.1 SARS-CoV-2 infections (95% CI, 2.0-2.1) per reported COVID-19 case were estimated to have occurred. CONCLUSIONS AND RELEVANCEBased on a sample of blood donations in the US from July 2020 through May 2021, vaccine-and infection-induced SARS-CoV-2 seroprevalence increased over time and varied by age, race and ethnicity, and geographic region. Despite weighting to adjust for demographic differences, these findings from a national sample of blood donors may not be representative of the entire US population.