Stroke Risk After COVID-19 Bivalent Vaccination Among US Older Adults

Area of Science:

• Immunology
• Epidemiology
• Public Health

Background:

• Regulatory agencies noted a potential safety concern for ischemic stroke in older adults following the Pfizer-BioNTech bivalent COVID-19 vaccine.
• This prompted an investigation into potential stroke risks associated with COVID-19 bivalent vaccines.

Purpose of the Study:

• To evaluate the risk of stroke following COVID-19 bivalent vaccination.
• To assess stroke risk after same-day administration of COVID-19 bivalent and influenza vaccines.
• To examine stroke risk after influenza vaccination alone.

Main Methods:

• A self-controlled case series study was conducted using Medicare beneficiaries aged 65 years and older.
• The study included over 5.3 million individuals vaccinated with COVID-19 bivalent vaccines between August 2022 and February 2023.
• Stroke events were analyzed within 1-21 day and 22-42 day windows post-vaccination compared to a 43-90 day control window.

Main Results:

• No statistically significant increase in stroke risk was observed after receiving either brand of the COVID-19 bivalent vaccine.
• A statistically significant association was found between the Pfizer-BioNTech bivalent vaccine and nonhemorrhagic stroke when given concomitantly with influenza vaccine.
• A statistically significant association was also found between the Moderna bivalent vaccine and transient ischemic attack when co-administered with influenza vaccine.

Conclusions:

• The study found no evidence of an elevated stroke risk in Medicare beneficiaries aged 65+ following COVID-19 bivalent vaccination.
• Concomitant administration of COVID-19 bivalent vaccines with high-dose or adjuvanted influenza vaccines showed some statistically significant associations with stroke outcomes.
• These findings suggest careful consideration for co-administration strategies in older adults.