Do Vaccines Cause Myocardial Infarction or Stroke?

Updated November 9, 2023



Myocardial infarction (MI) has been associated with natural influenza infection, and stroke has been associated with natural varicella infection, albeit both very rarely. Thus, influenza vaccine prevents MI and varicella vaccine prevents stroke by protecting against natural infection. Vaccines currently routinely recommended to the general population in the U.S.* have not been shown to cause myocardial infarction or stroke. Influenza vaccine has been associated with a reduced risk of stroke.

Epidemiological Evidence

The 2012 report by the Institute of Medicine (IOM), now called the National Academy of Medicine (NAM), described one study with sufficient validity and precision that reported a decreased risk of both MI and stroke within the first month after influenza vaccine 1. The report also described one study assessing stroke and varicella vaccine (Varivax®) 2, but this study did not provide convincing evidence due to a lack of validity and precision 3.

Since the 2012 IOM report, a matched case-control study of 78,706 persons found that receipt of seasonal influenza vaccine within the previous year was significantly associated with lower odds of MI (adjusted odds ratio: 0.81; 95% confidence interval: 0.77-0.85) and receipt of pneumococcal vaccine was not associated with a change in odds of MI in adults 4. Another matched case-control study of 94,022 persons found that receipt of seasonal influenza vaccine within-season was significantly associated with lower odds of stroke (aOR: 0.76; 95% CI: 0.72-0.80) and receipt of pneumococcal vaccine was not associated with a change in odds of stroke 5. A self-controlled case-series study of 17,853 persons found a reduction in incidence of stroke after receipt of influenza vaccine 6. In all three of these studies, early seasonal influenza vaccination (before mid-November) was much more beneficial than later seasonal influenza vaccination.

A 2017 meta-analysis also concluded that influenza vaccine was associated with a reduced risk of stroke (OR: 0.82; 95% CI: 0.75-0.91) 7.

A 2011 self-controlled case series found a decreased incidence of MI up to 60 days after seasonal influenza vaccination, ranging from a 32% reduction within the first 14 days (incidence rate ratio: 0.68; 95% CI: 0.60-0.78) to a 18% reduction within 29-59 days (IRR: 0.82; 95% CI: 0.75-0.90) 8.

A 2013 case-control study of 559 Australian patients also found decreased odds of MI after influenza vaccination (aOR: 0.55; 95% CI 0.35-0.85) 9. Pooled data from several studies examining adults with recent ischemic stroke found no association between influenza vaccination and MI or stroke 10.

Two case-control studies, one population-based cohort study, and one propensity score-matched retrospective cohort study of Taiwanese patients at least 65 years of age found decreased odds of cardiovascular events such as MI and stroke after influenza vaccination 11-14.

A 2019 Danish national population-based cohort study found influenza vaccination decreased the risk of stroke (and had no association with MI) among patients at least 65 years of age discharged from intensive care units 15.

A 2021 self-controlled case series using data from Norwegian national registers found a decreased risk of cardiovascular events such as MI and stroke following influenza vaccination, especially among higher-risk individuals (i.e., those using anti-diabetic, anti-obesity, anti-thrombotic, pulmonary, or cardiovascular medications) 16.

A 2021 randomized, double-blind, placebo-controlled, multicenter trial found that influenza vaccination shortly after an MI decreased the risk of a subsequent MI or cardiovascular mortality within the next year 17.

A 2014 review and meta-analysis suggested that among patients with coronary artery disease, influenza vaccination may lead to a decrease in incidence, morbidity, and mortality from MI (pooled relative risk: 0.39; 95% CI: 0.20-0.77) 18.

A 2015 Cochrane review determined that influenza vaccination may reduce cardiovascular mortality and combined cardiovascular events among patients with cardiovascular disease, although not enough evidence was available to establish whether influenza vaccination prevented primary cardiovascular disease 19.

A 2019 systematic review and meta-analysis of self-controlled case series studies found a decreased risk of MI in the four weeks after influenza vaccination (IRR: 0.84; 95%CI: 0.78-0.91) 20.

A 2021 systematic review and meta-analysis of studies among patients with cardiovascular disease found influenza vaccination associated with a lower risk of cardiovascular mortality and major cardiovascular events 21.

A 2021 systematic review determined influenza vaccination decreased risk of cardiovascular mortality and cardiovascular events such as MI 22.

Prospective cohorts of older adults found that receipt of pneumococcal polysaccharide vaccine was either not associated with MI or stroke 23,24 or associated with a decreased risk of acute coronary syndrome events in general 25,26. A prospective cohort of 27,204 Spanish individuals initially found a decreased risk of stroke in individuals receiving 23-valent pneumococcal polysaccharide vaccine (PPV) 27; however, this association was later refuted by the authors 28. This study did show that influenza vaccine was associated with reduced risk of death from stroke 29, and that pneumococcal vaccine was not associated with MI 30.

A retrospective observational study of adults hospitalized in the US found combined PPV and influenza vaccination was associated with a reduced risk of cardiac arrest and mortality among those admitted with MI or stroke 31. A 2020 systematic review and meta-analysis found PPV was associated with a reduced risk of cardiovascular events (RR: 0.91; 95% CI: 0.84-0.99) and MI (RR: 0.88; 95% CI: 0.79-0.98) 32.

A study in 193,083 adults at least 50 years of age found no association between herpes zoster vaccine and MI using both case-centered and self-controlled case series analyses 33. A population-based cohort study including 1.6 million Medicare beneficiaries receiving herpes zoster vaccine and 1.6 million propensity score-matched unvaccinated beneficiaries found that vaccination was associated with lower incidence of stroke 34. A self-controlled case series among Australians 70-79 years old found a decreased risk of stroke (relative incidence: 0.58; 95% CI: 0.44-0.78) and no change in the risk of MI in the 42 days after herpes zoster vaccination versus control periods 35. Herpes zoster vaccine was not associated with an increased risk of stroke or cardiovascular events in numerous other safety studies 36.

Two large Vaccine Safety Datalink studies found no association between stroke and receipt of quadrivalent HPV vaccine (Gardasil®) in females age 9 to 26 37 or receipt of the DTaP-IPV combination vaccine (Kinrix®) in children age 4 to 6 38, respectively. A review of quadrivalent HPV vaccine safety data published between 2006 and 2015 found no increase in incidence of stroke compared to background rates 39.

A 2020 self-controlled risk interval analysis of Taiwanese children using nationwide data found no increased risk of ischemic stroke after varicella vaccination 40. A 2015 international case-control study concluded that routine vaccinations in childhood appear to be protective against stroke 41.

Analyses of safety surveillance data from the Vaccine Safety Datalink found no significant associations between mRNA COVID-19 vaccines and 23 serious health outcomes (including acute myocardial infarction and stroke) 42. A self-controlled case series using national English data found an increased risk of hemorrhagic stroke 15-21 days after vaccination with Comirnaty, the Pfizer-BioNTech COVID-19 vaccine (IRR: 1.38; 95% CI: 1.12-1.71) 43. Another self-controlled case series analysis using national English data found an increased risk of ischemic stroke 15-21 days after vaccination with Comirnaty (IRR: 1.12; 95%CI: 1.04-1.20) 44. A self-controlled case series analysis using national French data found no increased risk of MI or stroke among persons at least 75 years old within 14 days of vaccination with Comirnaty 45.

Proposed Biological Mechanism

Potential mechanisms for MI include viral infection and alterations in the coagulation cascade 3. MI has been associated with natural influenza infection, albeit very rarely 20,46. Potential mechanisms for stroke include direct viral infection, viral reactivation, and alterations in the coagulation cascade 3. Stroke has been associated with natural varicella infection, at an incidence of about 1 in 15,000 cases 47.

The IOM concluded that the only mechanistic evidence for an association between MI and live attenuated influenza vaccine or between stroke and varicella vaccine was knowledge about the natural infections. The IOM also concluded that there was no mechanistic evidence for an association between stroke and influenza vaccine or between MI and inactivated influenza vaccine, as the publications reviewed provided little evidence beyond a temporal association 3.

* These conclusions do not necessarily consider vaccines recommended only for special populations in the United States such as Yellow Fever vaccine (international travelers) or Smallpox vaccine (military personnel), or vaccines no longer recommended to the public such as the Janssen (J&J) COVID-19 vaccine.


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