Expected Rates of Select Adverse Events following Immunization for COVID-19 Vaccine Safety Monitoring

Background Knowledge of expected rates of potential adverse events of special interest (AESI) that may occur coincidentally following COVID-19 vaccination is essential for vaccine safety surveillance and assessment. We calculated the expected rates of 21 potential AESI following COVID-19 vaccination among vaccinated persons within 1 day, 7 days, and 42 days of vaccination. Methods We used meta-analytic methods to estimate background rates of 21 medical conditions considered potential AESI and calculated expected rates of each potential AESI within 1 day, 7 days, and 42 days of vaccination. Results Background: rates of three commonly monitored AESI, Guillain-Barre syndrome (GBS), myopericarditis, and all-cause deaths were 2.0 GBS cases/100,000 person-years, 1.3 myopericarditis cases/100,000 person-years, and 863.8 all-cause deaths/100,000 person-years, respectively. Based on these background rates, if 10,000,000 persons are vaccinated, we would expect 0.5, 3.7, and 22.5 GBS cases; 0.3, 2.4, and 14.3 myopericarditis cases; and 236.5, 1655.5, and 9932.8 all-cause deaths to occur in coincident temporal association (i.e., as a result of background incidence) within 1 day, 7 days, and 42 days of vaccination, respectively. Conclusion Knowledge of expected rates of potential AESI can help contextualize adverse health events associated temporally with immunization, aid in safety signal detection, guide COVID-19 vaccine public health communication, and inform benefit-risk assessments of COVID-19 vaccines.