Impact of prior SARS-CoV-2 infection on incidence of hospitalization and adverse events following mRNA SARS-CoV-2 vaccination: A nationwide, retrospective cohort study

• Main Authors: Branch-Elliman, W. (Author), Do, N.V (Author), Fillmore, N.R (Author), La, J. (Author), Li, L.L (Author), Monach, P.A (Author), Strymish, J.M (Author), Zheng, C. (Author)
• Format: Article
• Language: English
• Published: Elsevier Ltd 2022
• Subjects: adult; Adverse events; aged; Aged; Article; clinical trial; cohort analysis; comorbidity; controlled study; coronavirus disease 2019; Covid-19; COVID-19; COVID-19 Vaccines; drug safety; elasomeran; falling; female; fever; hospitalization; Hospitalization; human; Humans; incidence; Incidence; longitudinal study; major clinical study; male; medical history; medical record review; messenger RNA; microbiological examination; middle aged; mortality; mortality risk; mRNA vaccine; mRNA Vaccines; multicenter study; recombinant vaccine; Retrospective Studies; retrospective study; RNA vaccine; RNA, Messenger; SARS-CoV-2; Severe acute respiratory syndrome coronavirus 2; side effect; Surveillance; tozinameran; Trigger tools; vaccination; Vaccination; Vaccines, Synthetic; veteran; weakness
• Online Access: View Fulltext in Publisher

 Background: Previous studies evaluated the SARS-CoV-2 vaccine safety or compared adverse events following vaccination to those from infection. Limited data about the impact of prior infection on post-vaccine adverse events are available. The objective of this study was to evaluate the impact of prior SARS-CoV-2 infection on outcomes shortly after vaccination using a longitudinal design. Methods: Nationwide, multicenter, retrospective cohort study of hospitalization, death, and pre-specified adverse event rates among Veterans who received mRNA vaccines within the Veterans Health Administration between 12/11/2020 and 8/31/2021. Daily incidence rates were compared before and after vaccine doses, stratified by history of microbiologically-confirmed SARS-CoV-2. Results: 3,118,802 patients received a first dose and 2,979,326 a second, including 102,829 with a history of SARS-CoV-2 infection. Daily incident hospitalization rates were unchanged before and after the second dose among patients without previous infection (28.8/100,000 post-dose versus 28.6/100,000 pre-dose, p = 0.92). In previously-infected patients, the hospitalization rate increased above baseline one day following vaccination (158.2/100,000 after dose 2 versus 57.3/100,000 pre-dose, p < 0.001), then returned to baseline. Chart review indicated vaccine side effects, such as fever, constitutional symptoms, weakness, or falls, as the definite (39%) or possible (18%) cause of hospitalization. Affected patients had mean age 75, and 90% had at least one serious comorbidity. Hospitalizations were brief (median 2 days), with rapid return to baseline health. Worse baseline health among previously-infected patients prevented conclusions about mortality risk. Conclusions: Two-dose mRNA vaccine regimens are safe in a population with many comorbidities. Transient increased risks of hospitalization were identified among patients with prior SARS-CoV-2, absolute risk ∼1:1000. Findings support additional study regarding the optimal dosing schedule in this population. Funding: None. © 2022