Association Between COVID-19 Vaccination and Sudden Death in Younger Adults: A Population-Based

Vaccination and Sudden Death in Young Adults: Design, Signals, and Interpretive Boundaries

Exposure assessment centered on prior COVID-19 vaccination.

• A population-based case-control study conducted in Ontario, Canada, targeting residents aged 12–50 years who were alive as of April 1, 2021.
• Exclusion criteria encompassed individuals older than 50, plus those with preexisting cardiovascular disease, mental illness, or conditions that elevate risk for adverse COVID-19 outcomes.
• Cases were defined as out-of-hospital deaths or deaths within 24 hours of hospital presentation with a final cardiac arrest diagnosis between April 1, 2021 and June 30, 2023.
• Each case was matched to five controls on age, sex, region, and neighborhood income quintile.

• The primary analysis employed conditional logistic regression to estimate the association between prior vaccination and sudden death, adjusting for a range of potential confounders, including SARS-CoV-2 test status, number of PCR tests, influenza vaccination, and common comorbidities.
• Sensitivity analyses were performed using alternative exposure definitions and subsets of cases with matched controls, in addition to a modified self-controlled case series (SCCS) among vaccinated individuals who met the case definition during the study window, allowing up to three vaccine doses.

• Among 6,365,451 eligible individuals, 4,963 cases met the sudden death criteria (approximately 0.08% of the cohort), with a median age of 36 years and 74.4% male.
• The analysis reports risk estimates for vaccination relative to sudden death, across doses, with results indicating lower or nonsignificant associations but not demonstrating increased risk.

P-values consistently indicated statistical significance for the primary exposure assessment.

• In the primary analysis, prior COVID-19 vaccination was associated with a reduced risk of sudden death in this population (adjusted odds ratio [aOR] 0.57; 95% CI 0.53–0.61).
• For the second dose, the rate ratio (RI) was 0.94 (95% CI 0.57–1.57; p = 0.82), and for the third dose, RI was 0.87 (95% CI 0.37–2.05; p = 0.10), reflecting imprecision and wide confidence intervals in these subgroup analyses.
• The study evaluated multiple analytic angles, including sensitivity analyses with alternative exposure definitions and a modified SCCS, to test robustness.

• Acknowledged limitations include the inability to definitively verify causes of all out-of-hospital deaths, potentially misclassification of sudden death cases, and residual confounding stemming from health-seeking behaviors that differ between cases and controls.
• The authors note that the findings do not support a hypothesis that COVID-19 vaccination elevates the risk of sudden cardiac death among young, apparently healthy adults; instead, vaccination was associated with a lower observed risk in the primary analysis.
• The results are contingent on observational methods and linked administrative datasets, with limitations inherent to such designs.