Results
From June 18, 2022 to March 18, 2023, 135 005 doses of Pfizer-BioNTech COVID-19 vaccine were given to children aged 6 months to 4 years, and 112 006 doses of Moderna COVID-19 vaccine were given to children aged 6 months to 5 years in the VSD population (Table 1). For most outcomes, including myocarditis and pericarditis, no events occurred in the risk interval (Table 2). RRs were not elevated for any prespecified outcomes following any dose of Pfizer-BioNTech and Moderna vaccine, and none of the outcomes met the signaling threshold of P < .011. For example, the RR for convulsions and seizures in 0 to 7 days postvaccination was 0.64 (95% CI: 0.25–1.51, P = .89) after Pfizer-BioNTech and 0.85 (95% CI: 0.27–2.32, P = .70) after Moderna. One case of hemorrhagic stroke and 1 case of pulmonary embolism were identified after vaccination; however, chart review found each outcome was unrelated to vaccination (both children had congenital abnormalities).