Association Between COVID-19 Vaccination and Sudden Death in Young Healthy Adults: A Population-

The authors note concerns about rare but serious adverse events (myocarditis, immune thrombotic thrombocytopenia) and address the hypothesis that vaccination could elevate the risk of sudden death in young healthy adults.

• This population-based case-control study investigates whether COVID-19 vaccination is associated with an increased risk of sudden death in apparently healthy individuals aged 12–50 years.

• Data source: Linked administrative datasets for residents of Ontario, Canada, alive as of April 1, 2021.
• Population: Excluded individuals over 50 and those with preexisting cardiovascular disease, mental illness, or conditions that predispose to adverse COVID-19 outcomes.
• Case definition: Death out of hospital, or death within 24 hours of hospital presentation with a final diagnosis of cardiac arrest, between April 1, 2021 and June 30, 2023.
• Control selection: Each case matched to five controls by age, sex, region of residence, and neighborhood income quintile.
• Exposure assessment: COVID-19 vaccination status prior to the event, with adjustments for potential confounders.

• Primary method: Conditional logistic regression to estimate the association between prior vaccination and sudden death, adjusting for several potential confounders, including prior SARS-CoV-2 testing and vaccination history, influenza vaccination, and comorbidities.
• Sensitivity analyses included alternative exposure definitions and subsets of cases with matched controls.
• A secondary analysis used a modified self-controlled case series (SCCS) among vaccinated individuals meeting the case definition, allowing up to three vaccine doses.

The results suggest no evidence that vaccination increases the risk of sudden death in this population.

The report notes wide confidence intervals that reflect uncertainty for these strata.

• Sample and cases: Among 6,365,451 eligible individuals, 4,963 cases of sudden death were identified (median age 36; 74.4% male).
• Primary analysis: Vaccination was associated with a lower risk of sudden death (adjusted odds ratio [aOR] 0.57; 95% CI 0.53–0.61; p-value reported as p < 0.001).
• Dose-specific results: For the second and third vaccine doses, estimates did not indicate an elevated risk (second dose RI 0.94; 95% CI 0.57–1.57; p = 0.82; third dose RI 0.87; 95% CI 0.37–2.05; p = 0.10).
• Self-controlled analysis: The SCCS analysis was conducted as a supplementary sensitivity check, focusing on vaccinated individuals meeting the case definition during the study period.

• Inability to confirm the exact cause of all out-of-hospital deaths, which could introduce misclassification.
• Residual confounding due to differences in health-seeking behaviors between vaccinated and unvaccinated individuals, potentially affecting the case-control estimates.

• The study does not support the hypothesis that COVID-19 vaccination increases the risk of sudden cardiac death among apparently healthy young adults.