Background. We studied the safety and reactogenicity SARS-CoV-2 mRNA vaccines in transplant recipients because immunosuppressed patients were excluded from vaccine trials. Methods. US transplant recipients were recruited into this prospective cohort study through social media; those who completed the full vaccine series between December 9, 2020 and March 1, 2021 were included. We collected demographics, medical history, and safety information within 7 d after doses 1 and 2 (D1, D2). Associations between characteristics and reactions were evaluated using modified Poisson regression. Results. We studied 741 transplant recipients who underwent BNT162b2 (54%) or mRNA-1273 (46%) vaccination. Median (interquartile range) age was 60 (44-69) y, 57% were female, and 10% were non-White. Although local site reactions decreased after D2 (85% D1 versus 78% D2, P < 0.001), systemic reactions increased (49% D1 versus 69% D2, P < 0.001). Younger participants were more likely to develop systemic symptoms after D1 (adjusted incidence rate ratio [aIRR] per 10 y = 0.850.900.94, P < 0.001) and D2 (aIRR per 10 y = 0.910.930.96, P < 0.001). Participants who experienced pain (aIRR = 1.111.662.47, P = 0.01) or redness (aIRR = 1.833.928.41, P < 0.01) were more likely to develop an antibody response to D1 of mRNA vaccines. No anaphylaxis, neurologic diagnoses, or SARS-CoV-2 diagnoses were reported. Infections were minimal (3% after D1, <0.01% after D2). One patient reported incident acute rejection post-D2. Conclusions. In solid organ transplant recipients undergoing mRNA vaccination, reactogenicity was similar to that reported in the original trials. Severe reactions were rare. These early safety data may help address vaccine hesitancy in transplant recipients.
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