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What do we know about heart and blood issues associated with COVID-19 vaccines and infections?

by Health Desk |Published on November 30, 2021 – Updated on May 11, 2022 | Explainer


What our experts say

People who have not been vaccinated are still being impacted with heart issues such as myocarditis, pericarditis, blood clots, strokes, heart attacks, and other ailments just as they were before the pandemic began.

However, COVID-19 increases the risk of blood clots and many other health issues dramatically. People who have not been vaccinated against the virus face much higher risks of severe symptoms from an infection than those who have been fully vaccinated.

Simply put, being unvaccinated greatly increases your risk of acquiring the virus and severe symptoms caused by it, hospitalization, and even death.

For instance, a recent study found that people who suffered blood clots after receiving the Oxford-AstraZeneca vaccine were much fewer in number than the people infected with COVID-19. 66 people out of roughly 10 million who received the first jab of the vaccine were found to be at risk for blood clots in the veins. In comparison, 12,614 people out of 10 million reported blood clots in the group who tested positive for the virus.

It should be noted that there have been a small amount of people who reported symptoms of myocarditis, pericarditis, and thrombocytopenia (low platelet count) after receiving a COVID-19 vaccine. Evidence has reportedly shown that the majority of these cases have been easily treated and that these conditions occur much more frequently in people who have been infected with the virus. One recent study in the United States noted that from March 2020 through January 2021, patients with COVID-19 had almost 16 times the risk for myocarditis compared with patients who were not infected, and risk varied by sex and age.

Another recent study found that myocarditis was more common after a COVID-19 infection than after a full COVID-19 vaccine course and noted that up to 28% of hospitalized patients with the virus showed clinical signs of myocardial injury

Heart issues caused by the virus are almost always more severe and cause worse health outcomes in people with infections as opposed to those who received the vaccines. This is likely due to their heart being damaged directly by the virus and causing inflammation or potentially the effect of inflammatory proteins being released into the blood.

Further, COVID-19 is closely associated with an increased risk in blood clots and inflammation in the vascular lining, especially in the heart and lungs. This can lead to poor oxygen levels and delivery to organs and increase the risk of heart attack and stroke.

Even without the risk of COVID-19 or related vaccines, cardiovascular disease is the leading cause of death globally, representing 32% of all deaths. Three-quarters of these deaths occur in low- and middle-income countries where a majority of people have not been vaccinated against COVID-19, clearly demonstrating that unvaccinated people were experiencing cardiac issues before and during the pandemic. 25% of all people around the world are dying from conditions linked to thrombosis (blood clots). Given that COVID-19 causes significantly more blood clots in infected patients than the vaccine may, the unvaccinated are at a significantly greater risk than the vaccinated population.

Context and background

Some people, particularly in the U.S., have speculated on social media that the Omicron variant is serving as a cover-up for the vaccines causing heart-related issues. Some of these posts also claim that unvaccinated people are not experiencing illnesses like heart attacks or myocarditis during the pandemic whereas vaccinated people are and at a much higher levels.

The Omicron variant was first identified by the nation of South Africa in November of 2021. After scientists there sequenced the genetic material of virus samples, they alerted the general public internationally due to the number of mutations the virus has and the likelihood that it could be highly transmissible. The World Health Organization then labeled the Omicron a "variant of concern" but noted that we need more information about the omicron before we understand how it works.

Given that the Omicron was first identified outside of the U.S. and the fact that people infected with COVID-19 have a much higher risk of virus-related heart issues, the idea that this variant is a cover-up is inaccurate. Unvaccinated and vaccinated people are still facing the daily risk of heart disease and blood clots they did before the pandemic started, but due to the virus, the unvaccinated are much more likely to develop severe COVID-19 infections and symptoms like blood clots, myocarditis, and stroke than those who have received the jabs.

Studies have shown that post-vaccine myocarditis or inflammation of the heart is an adverse effect seen in younger men, but is extremely rare and usually resolves within days or weeks. As per the U.S. Centers for Disease Control and Prevention, the risk of myocarditis due to infection from COVID-19 is about 16 times that of not getting infected. The benefits of vaccines have been shown to far outweigh the risks associated with them. The American Heart Association, the American Academy of Pediatrics, Canadian Cardiovascular Society, Heart and Stroke Foundation of Canada, and many such organizations continue to encourage all eligible people to get vaccinated against COVID-19.

A paper published in Scientific Reports drew conclusions from its analysis of Israel’s emergency medical services (EMS) data, suggesting an increase in emergency cardiovascular events in people under-40 is linked to COVID-19 vaccination. The authors associated an increase in EMS calls related to cardiac arrests (CA) or arrhythmia and acute coronary syndrome (ACS) or heart attack for ages 16 to 39 across Israel with an increase in their vaccination rates. The conclusions of this widely circulated study have been criticized for several oversights and the editors of the journal are re-considering the paper.

Firstly, the data used for this study was at a population level, which means that the authors did not know whether the individuals experiencing CA or ACS were vaccinated against COVID-19 or not, whether they had tested positive for COVID-19 or if the people calling EMS had any other medical conditions. Without knowing these details about the individuals, making claims for an entire population of a given age group is not reliable. The paper does not discuss any other plausible reasons for an apparent increase in CA or ACS cases after the changes in conditions, lifestyle, or other factors owing to the pandemic or even the expected monthly changes in cardiac events.

Furthermore, some scientists have delved deeper into the mathematical calculations done for this study and have found several errors. They have not been able to replicate the findings of the study either. Simultaneously, another study conducted in the UK on similar research with more robust data on individual patients, and their conclusions suggest that there is no evidence to suggest an increased risk of cardiac deaths in younger individuals in the first six weeks after being vaccinated.

Additionally, Israel’s Ministry of Health had already published a study based on hospital data comparing vaccinated and unvaccinated people for a range of outcomes. Similar to other studies conducted in other countries, they had found an increased risk of myocarditis, but no other heart conditions.


  1. Myocarditis after COVID-19 mRNA vaccination: clinical observations and potential mechanisms (Nature)
  2. Association Between COVID-19 and Myocarditis Using Hospital-Based Administrative Data — United States, March 2020–January 2021 (U.S. CDC)
  3. Myocarditis after Covid-19 Vaccination in a Large Health Care Organization (New England Journal of Medicine)
  4. Safety of the BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Setting (New England Journal of Medicine)
  5. Risks of myocarditis, pericarditis, and cardiac arrhythmias associated with COVID-19 vaccination or SARS-CoV-2 infection (Nature Medicine)
  6. PubPeer comments on ‘Increased emergency cardiovascular events among under-40 population in Israel during vaccine rollout and third COVID-19 wave’ (PubPeer)
  7. Myocarditis after BNT162b2 mRNA Vaccine against Covid-19 in Israel (New England Journal of Medicine)
  8. Cardiovascular and haematological events post COVID-19 vaccination: A systematic review (Journal of Cellular and Molecular Medicine)
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  10. COVID Vaccines Don’t Cause Heart Disease (Voices for Vaccines)
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  12. Heart inflammation, COVID-19 and the rare side effects of the vaccine (UC Davis Health)
  13. Myocarditis and Pericarditis After mRNA COVID-19 Vaccination (United States Centers for Disease Control and Prevention)
  14. Covid-19 vaccines: In the rush for regulatory approval, do we need more data? (The BMJ)
  15. Vaccine-induced immune thrombotic thrombocytopenia (The Lancet Haematology)
  16. Safety of the BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Setting (The New England Journal of Medicine)
  17. COVID-19 Messenger RNA Vaccination and Myocarditis—A Rare and Mostly Mild Adverse Effect (JAMA Internal Medicine)
  18. Cardiovascular diseases (CVDs) (World Health Organization)
  19. World Thrombosis Day (WTD)
  20. Update on Omicron (World Health Organization)
  21. Copyright-free photo by thirdman94 through Used with Permission from Health Desk, a public health hub that explains emerging COVID-19 science.
This article was written and edited by the Tayo editorial desk and has been reviewed by an independent panel of subject matter experts.

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