Variable Definition
Age was recorded at the time of transfusion. Sex (male or female), race (white, black, other, or multirace) and ethnicity (Hispanic or non-Hispanic) were self-reported at enrollment. BMI was calculated using height and weight at enrollment. The date of transfusion was used as a surrogate for variant. Transfusions before 15 June 2021 were classified as during the pre-Alpha/Alpha wave, and those from 15 June to 1 October 2021 as during the Delta wave. We used the self-reported time of symptom onset to calculate the time from symptom onset to transfusion. Baseline comorbid conditions were self-reported at day 0. Vaccination status was defined as fully vaccinated (≥2 weeks from the final dose in the primary vaccine series to transfusion), partially vaccinated (receipt of 1 dose in a 2-dose primary vaccine series or <2 weeks from the final dose in the primary vaccine series to transfusion) or unvaccinated.