There is conflicting evidence around the theory that certain COVID-19 vaccines might increase the risk of stroke. However, the likelihood of stroke may be higher in unvaccinated people who develop COVID-19.

Therefore, the benefits of the vaccine outweigh the risk of stroke.

The COVID-19 vaccination helps protect against contracting SARS-CoV-2. If a person contracts the virus, they can develop COVID-19. This illness has resulted in around 6 million deaths worldwide.

This article summarizes what scientists currently know about COVID-19 vaccines and the risk of stroke.

It discusses whether these vaccines are risk factors for stroke and whether they are safe for people who have already had a stroke. It also provides information about the signs of stroke.

Coronavirus data

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date. Visit our coronavirus hub for the most recent information on COVID-19.

COVId-19 vaccines on a tray 2Share on Pinterest
Morsa Images/Getty Images

Scientists are unsure about the link between COVID-19 vaccines and the risk of stroke.

According to the National Institutes of Health (NIH), a stroke occurs when reduced blood flow within the brain causes many brain cells to die. There are two main types of stroke:

  • Ischemic stroke: These strokes occur when there is a decreased blood supply to a part of the brain. This can happen when brain arteries gradually narrow, decreasing blood flow. These can also occur when a blood clot suddenly and completely blocks an artery.
  • Hemorrhagic stroke: These strokes occur when a blood vessel bursts within the brain. Blood leaks out, depriving brain cells downstream of oxygen and nutrients. This blood leak can also send toxic chemicals into the surrounding cells and increase pressure within the skull. These processes may further harm brain cells.

The Centers for Disease Control and Prevention (CDC) state that in the early stages of vaccine roll-outs, some data indicated that the Pfizer-BioNTech COVID-19 vaccine could be a risk factor for ischemic stroke. However, the recent data sources about more recent vaccines do not indicate the same finding.

A 2022 review makes similar points, regarding the seemingly conflicting data on COVID-19 and the risk of stroke. While some studies indicate that the vaccines could be risk factors for ischemic and hemorrhagic strokes, others do not.

Why might the vaccine increase stroke risk?

Because there are so many unknowns, it is difficult to speculate about what might explain any connection between COVID-19 vaccines and the likelihood of stroke.

The 2022 review suggests that the vaccines could cause known risk factors for ischemic and hemorrhagic stroke. These include:

A 2022 study found evidence that such risk factors were likelier to develop in people who had received a COVID-19 vaccine than in the general population.

However, such risk factors were also more common in those who have COVID-19 than in the general population.

According to the above 2022 review, the risks of not receiving the COVID-19 vaccine are greater than the stroke risks from the vaccine.

The CDC concurs with this finding, advising against changes to vaccination practice, as an increase in the risk of stroke is so uncertain.

In addition, the American Heart Association (AHA) argues that people who have had a stroke would likely benefit from receiving a COVID-19 vaccine.

Therefore, the risk of stroke may actually be higher among unvaccinated individuals who develop COVID-19 than in people who receive the vaccine.

When strokes cause brain cells to die, this process can result in various neurological symptoms. According to the NIH, these symptoms include:

  • sudden confusion
  • sudden speaking difficulties, or difficulties understanding speech
  • sudden weakness or numbness in the arm, face, or leg, which may affect only one side of the body
  • sudden vision problems, in one eye or both, such as double vision
  • sudden dizziness
  • sudden loss of balance, coordination,
  • sudden difficulties walking
  • sudden severe headache

A stroke is a serious medical emergency. If an individual experiences these symptoms or notices that someone else has them, they must call emergency services right away.

Strokes are potentially life threatening conditions where not enough blood reaches a person’s brain. These health events can kill off brain cells.

There is some evidence that certain COVID-19 vaccines can increase risk factors for stroke. These risk factors include blood clots, high blood pressure, and low platelet counts. However, scientists remain unsure whether this translates into an elevated risk of stroke.

While early studies suggested some vaccines might have this effect, several vaccines never appeared to affect the risk of stroke. Furthermore, more recent studies have failed to discover robust links between COVID-19 and stroke risk. Scientists continue to study this topic.

Many doctors and scientists believe that, on balance, receiving these vaccines is less dangerous than not. This is true of people who have already had a stroke, as well as the general population.