Research Summary

Ontario Study Finds No Association Between COVID Vaccination, Sudden Death

Edited by:
Kate Young

Key Highlights

  • In Ontario residents aged 12 to 50 years without major documented comorbidities, COVID-19 vaccination was not associated with increased odds of sudden death.
  • The primary analysis found lower adjusted odds of sudden death among vaccinated individuals versus matched controls.  
  • Sensitivity analyses, including vaccination within 6 weeks before death and a modified self-controlled case series, also showed no significant increase in risk.

A population-based case-control study published in PLOS Medicine found no evidence that COVID-19 vaccination increased the risk of sudden death among apparently healthy younger individuals in Ontario, Canada. The study addressed concerns that vaccination might be associated with sudden cardiac death in people aged 12 to 50 years without documented cardiovascular disease or other major illnesses predisposing to premature death.

Researchers used linked administrative health datasets from Ontario and identified residents alive on April 1, 2021. After extensive exclusions, including age 50 years or older, cardiovascular disease, diabetes, cancer, chronic kidney or liver disease, schizophrenia, frailty, and other conditions that could confound the analysis, 6,365,451 eligible individuals remained. Cases were defined as out-of-hospital deaths or deaths occurring in the emergency department or within 24 hours of hospital admission with diagnoses consistent with cardiac arrest, sudden death, or ventricular arrhythmia. Each case was matched with up to 5 controls by age, sex, geographic area, and neighborhood income quintile. Exposure was receipt of any COVID-19 vaccine, and the primary analysis used conditional logistic regression adjusted for recent and prior SARS-CoV-2 testing, influenza vaccination, PCR testing frequency, asthma, hypertension, and mood or anxiety disorders.

Study Findings

Among 6,365,451 eligible individuals, investigators identified 4,963 cases of sudden death during the study period from April 1, 2021, through June 30, 2023; 4,806 cases were included in the primary matched analysis. The median age of cases was 36 years, and 74.4% were male. Prior COVID-19 vaccination was documented in 67.4% of cases and 77.1% of controls. In the primary model, vaccination was associated with lower odds of sudden death (aOR, 0.57; 95% CI, 0.53-0.61; P < .001).

The findings were consistent across sensitivity analyses. Vaccination within 6 weeks before the index date was also not associated with increased risk (aOR, 0.63; 95% CI, 0.55-0.72). Results were similar in people younger than 40 years (aOR, 0.53; 95% CI, 0.48-0.58), in those who died in hospital or the emergency department (aOR, 0.71; 95% CI, 0.55-0.91), and after exclusion of opioid-related deaths (aOR, 0.57; 95% CI, 0.51-0.64). In a modified self-controlled case series, no significant increase in sudden death rate was seen in the 6 weeks after dose 1 (RI, 0.87), dose 2 (RI, 0.94), or dose 3 (RI, 0.87).

Clinical Implications

According to the study authors, the findings do not support the hypothesis that COVID-19 vaccines increase the risk of sudden cardiac death in young healthy adults. They wrote that the results may help address concerns that could discourage future vaccination.

The main limitations reported by the authors were the inability to confirm the cause of out-of-hospital deaths and the potential for residual confounding related to differences in healthcare-seeking behavior. They also noted that undiagnosed disease could not be fully excluded in registry-based analyses.

Expert Commentary

“These data do not support the hypothesis that COVID-19 vaccines increase the risk of sudden cardiac death,” the researchers concluded.

Reference
Abdel-Qadir H, Bhatt HA, Swayze S, et al. Association between COVID-19 vaccination and sudden death in apparently healthy younger individuals: A population-based case-control study. PLoS Med. 2026;23(3):e1004924. doi:10.1371/journal.pmed.1004924.