The COVID-19 pandemic led to the rapid development and global rollout of vaccines. Public interest focused on their safety, including concerns about a potential link between vaccination and stroke. This article addresses these concerns by presenting evidence-based information on vaccine safety and stroke risk.
Understanding Stroke
A stroke occurs when the blood supply to part of the brain is interrupted or reduced, depriving brain tissue of oxygen and nutrients. Brain cells can begin to die within minutes. There are two primary types: ischemic stroke, caused by a blocked blood vessel, and hemorrhagic stroke, caused by a ruptured blood vessel leading to bleeding in the brain.
Several factors increase stroke risk, including high blood pressure, diabetes, high cholesterol, smoking, heart disease, and increasing age. Understanding these established risk factors provides context when examining potential associations with new medical interventions.
COVID-19 Vaccine Safety and Stroke Risk
Extensive monitoring and large-scale studies have investigated the safety of COVID-19 vaccines, including any potential link to stroke. Major health organizations, such as the Centers for Disease Control and Prevention (CDC), the Food and Drug Administration (FDA), and the World Health Organization (WHO), have continuously analyzed data from comprehensive surveillance systems. Systems like the Vaccine Adverse Event Reporting System (VAERS) in the United States and EudraVigilance in Europe collect reports of adverse events following vaccination, allowing for ongoing safety assessments.
Overall data indicates no broad causal link between COVID-19 vaccines and an increased risk of typical strokes. Studies have shown post-vaccination acute arterial ischemic stroke events are significantly less frequent than strokes in the general population or among individuals hospitalized with COVID-19. A large study of over 5 million Medicare beneficiaries who received bivalent mRNA vaccines also found no statistically significant associations with nonhemorrhagic, transient ischemic, or hemorrhagic strokes.
While the general risk of stroke is not increased by COVID-19 vaccines, rare clotting disorders, specifically Thrombosis with Thrombocytopenia Syndrome (TTS), have been associated with certain adenoviral vector vaccines, such as those from Johnson & Johnson (Janssen) and AstraZeneca. TTS involves blood clots combined with low platelet levels and can occur in unusual locations, including the brain (cerebral venous sinus thrombosis). These events are extremely rare, with estimates around 7 cases per 1 million doses for the J&J vaccine. The risk of experiencing TTS is considerably lower than the risk of blood clots from COVID-19 illness itself.
In January 2023, a preliminary safety signal for ischemic stroke in adults aged 65 years or older was identified in the CDC’s Vaccine Safety Datalink (VSD) following the Pfizer-BioNTech bivalent COVID-19 vaccine. However, subsequent analyses across multiple other surveillance systems, including VAERS, the Centers for Medicare & Medicaid Services database, and the Veterans Affairs database, did not confirm this signal. The CDC and FDA concluded that it was very unlikely this signal represented an actual clinical risk, and no changes to vaccination practices were recommended. Further studies also found no increased risk of ischemic stroke within 21 days after bivalent vaccination.
COVID-19 Illness and Stroke Risk
In contrast to the minimal association with vaccines, contracting COVID-19 disease significantly increases the risk of various cardiovascular complications, including stroke. Research indicates that the risk of stroke is highest within days of a COVID-19 diagnosis and can remain elevated for months after infection. This increased risk is attributed to several mechanisms related to the body’s response to the virus.
COVID-19 can trigger an inflammatory response throughout the body, damaging blood vessels and promoting blood clot formation. The virus can infect endothelial cells lining blood vessels, leading to the release of pro-inflammatory factors that activate platelets and other clotting components. Additionally, COVID-19 can induce a hypercoagulable state, meaning the blood becomes more prone to clotting.
Studies have consistently shown a substantially higher risk of thromboembolic and ischemic events, including stroke, after SARS-CoV-2 infection compared to after vaccination. For example, one meta-analysis highlighted that the prevalence of acute arterial ischemic stroke was approximately 200 times lower following COVID-19 vaccination than in patients hospitalized with COVID-19. Therefore, vaccination plays an important role in reducing the risk of severe COVID-19 and its associated complications, including stroke.
Recognizing Stroke Symptoms
Recognizing the signs and symptoms of a stroke is crucial for timely medical intervention, regardless of vaccination status. Immediate medical attention can significantly improve outcomes and reduce brain damage. A simple acronym, F.A.S.T., helps people remember the most common indicators of a stroke.
F.A.S.T. stands for:
Face drooping: One side of the face may droop or feel numb. Ask the person to smile to see if it is uneven.
Arm weakness: One arm may feel weak or numb. Ask the person to raise both arms. See if one arm drifts downward.
Speech difficulty: Speech may be slurred, or the person may have trouble speaking or understanding. Ask them to repeat a simple sentence.
Time to call emergency services: If any of these signs are present, even if they disappear, call for emergency medical help immediately.
Other sudden symptoms can include weakness or numbness on one side of the body, sudden blurred vision, confusion, dizziness, unsteadiness, or a severe headache. Even if symptoms are brief, they could indicate a transient ischemic attack (TIA), also known as a mini-stroke, which is a warning sign for a future stroke and requires urgent medical attention.