(357) Risks of Cardiovascular Events Following COVID-19 Vaccination – Results From a Nationwide Cohort Study of 8 Million Swedish Adults

Background: While the rationale for vaccination for COVID-19 is to reduce complications and overall survival, some cardiovascular complications to the vaccine itself have been demonstrated. In younger age groups, myocarditis and pericarditis are recognized as rare acute adverse events after mRNA vaccines.

Objectives: To investigate risks of adverse cardiovascular events after vaccination. We hypothesized that underlying mechanisms of vaccine-related myopericarditis could manifest as other adverse cardiovascular events in other age groups, with varying time lags.

Methods: This is a nationwide register-based cohort study of all Swedish adults (n=8,070,674) with a study period from 27 December 2020 (start date of vaccinations in Sweden) to 31 December 2022. Data were obtained from national registers.
Exposure was COVID-19 vaccination, by dose (1, 2 and 3) and vaccine product (BNT162b2, mRNA-1273 and AZD1222).
Outcomes were dysrhythmias [extrasystoles, atrial fibrillation (AF) and arrhythmias], heart failure (HF), myocardial infarction (MI), and cerebrovascular events [transit ischemic attack (TIA) and stroke], together with myopericarditis as a positive control.
We used Cox regression to estimate post-vaccination risks for each outcome in five mutually exclusive risk windows [1-7 days (week 1), 8-14 days (week 2), 15-21 days (week 3), 22-28 days (week 4), and 29-42 days (week 5-6)] after each dose compared to unvaccinated status, with adjustments for potential confounders (sociodemographics, prior comorbidities and drugs, and time-varying first COVID-19 infection).

Results: Most of the outcomes showed decreased risks after vaccination, especially after dose 3 (overall HRs ranged from 0.69 to 0.81 for AF, arrhythmias, HF, MI and stroke in 1-6 weeks after dose 3), while we also replicated the increased risk for myopericarditis within 4 weeks after one or two doses of mRNA vaccination [e.g., HR=4.52 (3.25-6.30) after second dose of mRNA-1273)]. Slightly increased risks, similar across vaccine products, were observed for extrasystoles in 1-6 weeks after the first two doses [HR 1.17 (1.06-1.28) for dose 1 and HR 1.22 (1.10-1.36) for dose 2]. The increased risks were stronger in older adults and males. A similar risk was observed for TIA in 1-6 weeks after dose 2 [HR 1.13 (1.05-1.23)], mainly in older adults.

Conclusions: While there is a transient increase in the risk of myopericarditis (mRNA vaccines only), extrasystoles (but not for arrhythmias) and TIA (but not for stroke) following COVID-19 vaccines, it’s important to note that full vaccination substantially reduces the risks of more severe complications associated with COVID-19, underscoring that the risks are outweighed by the benefits of complete vaccination.