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.

Between November 1999 and August 2002, consenting adult elective cardiac surgery patients at Oregon Health & Science University, Portland Veteran’s Administration Medical Center, and St. Vincent’s Hospital who were undergoing cardiopulmonary bypass (CPB) were randomized at admission to receive either prestorage leukoreduced red cells (PSL-RBCs) or standard red cells (S-RBCs) in a prospective double-blind fashion. Only data from those transfused were analyzed. Outcome measures included death at 60 days, 60 day infection rate, and length of hospital stay (LOS). Patients at all 3 institutions were operated on by the same group of cardiovascular surgeons. Given higher baseline infection rates for coronary artery bypass grafts (CABG) randomization was stratified by CABG vs valve replacement (VR). All RBCs were issued with blinding hoods. All platelet transfusion were prestorage leukoreduced. RBC transfusion rates were 30% for CABG, 38 % for VR, and 63% for CABG + VR. Infections were determined by infection control nurses using standardized Centers for Disease Control criteria from hospital surveillance and records and follow-up phone calls. Deaths were determined from hospital records and follow-up calls, and verified by National Death Index data. The PSL-RBC arm included 304 patients and the S-RBC arm 258 patients. The two groups were well-matched demographically and by cardiovascular risk factors. Intent-to-treat analysis showed a 60 day mortality of 9.7% in the S-RBC arm and of 4.9% in the PSL-RBC arm (p=0.029). Heart failure as the sentinel cause of death accounted for most of the difference (45.5% of deaths in the S-RBC group vs 13.3% in the PSL-LR group). Death rates were procedure specific: CABG alone > CABG + VR > VR alone. There was no significant difference between the S-RBC and PSL-RBC groups with regard to overall infection rate at 60 days. Most infections were superficial wound infections in the CABG patients; however groups did not differ in more serious infections such as bacteremia (p=0.369) or pneumonia (p=0.360). There was no significant difference between the groups with respect to LOS exclusive of in-hospital deaths. Our results essentially replicate in a North American context those of a previous European trial (Van de Watering et al Circulation1998; 97:562) involving elective cardiac surgery patients undergoing CABG and/or VR surgery randomized to receive S-RBCs prepared by the European buffy coat method vs leukoreduced RBCs. Despite technical differences in RBC preparation, the excess deaths in both studies in the S-RBC group vs the leukoreduced group suggests that elective cardiac surgery patients undergoing CPB constitute an at-risk group both in the US and Europe which may benefit from use of PSL-RBC. The significance of transfusion-related immunomodulation (TRIM) in man has been the subject of intense controversy. Interestingly the cause of the increased mortality in the S-RBC group, both in this study and the European study, could not be explained by differences in infection rates. Given the preponderance of deaths in the CABG patients it is tempting to speculate this may reflect an interaction between residual passenger leukocytes and ischemia which is independent of the TH1/TH2 lymphocyte shift postulated to underlie TRIM.

No abstract