Slightly Increased Stroke Risk With Covid-19, Flu Vaccines Investigated

Some older recipients of Covid-19 vaccines might express concern about stroke risks when receiving their shots, especially if they are vaccinated against influenza at the same time. Here is what the CDC and FDA say about the risk, which is considered far outweighed by the dangers of older adults contracting Covid or influenza.

SILVER SPRING, MD – Earlier this year, both the U.S. Food and Drug Administration and the national Centers for Disease Control and Prevention noted a safety concern for ischemic stroke in adults 65 years and older receiving COVID-19 bivalent vaccine.

Now, results are available from a self-controlled case series analysis which evaluated stroke risk among older Medicare fee-for-service beneficiaries receiving 1) a Pfizer-BioNTech (BNT162b2; WT/OMI BA.4/BA.5) or Moderna (mRNA-1273.222) COVID-19 bivalent vaccine, 2) high-dose/adjuvanted influenza vaccines, and 3) concomitant COVID-19 bivalent vaccines and influenza vaccines, from August 31 to November 6, 2022.

The medical claims review of more than 5.3 million adults found no increased risk of stroke in the overall group after Covid-19 vaccination. Looking specifically at vaccine recipients 85 and older, the FDA-led researchers found an elevated risk of strokes caused by blood clots in those who were given Pfizer vaccines, but not Moderna shots.

The preprint study – meaning it has not yet been peer-reviewed and published in a medical journal – also identified a slightly increased risk of blood clots in the brains of adults 65 and older who got a bivalent vaccine and high-dose or adjuvanted flu shot at the same time.

The authors explained, “The primary analysis did not find elevated stroke risk following COVID-19 bivalent vaccines. In the age subgroup analyses, only the ≥85 year age group had a risk of NHS (Incident Rate Ratio (IRR)=1.36, 95% CI 1.09 – 1.69 [1-21 days]) and NHS/TIA (IRR=1.28, 95% CI 1.08 – 1.52 [1-21 days]) with BNT162b2 Bivalent WT/OMI BA.4/BA.5. Among beneficiaries receiving a concomitant COVID-19 bivalent vaccine and a high-dose/adjuvanted influenza vaccine, an increased risk was observed for NHS (IRR=1.20, 95% CI 1.01 – 1.42 [22-42 days]) with BNT162b2 Bivalent WT/OMI BA.

Presenting at a late October meeting of CDC’s Advisory Committee on Immunization Practices (ACIP), Tom T. Shimabukuro, MD, MPH, MBA, the director of the agency’s Immunization Safety Office Division of Healthcare Quality Promotion, noted that a statistical signal for ischemic stroke after Pfizer-BioNTech bivalent mRNA COVID-19 vaccine was detected in CDC’s Vaccine Safety Datalink in recipients 65 and older in the fall of 2022, and it was presented at prior ACIP meetings.

“Available data do not provide clear and consistent evidence of a safety problem for ischemic stroke with bivalent mRNA COVID-19 vaccines when given alone or given simultaneously with influenza vaccines, or when influenza vaccine is given alone,” Shimabukuro explained. “Variable and inconsistent results were obtained in some analyses of the risk of ischemic stroke following bivalent mRNA COVID-19 vaccination, simultaneous bivalent mRNA COVID-19 and influenza vaccination, and influenza vaccination alone. Most study results have not shown an association between vaccination and ischemic stroke, and no clear pattern demonstrating increased risk has emerged.”

He also emphasized that any real or theoretical risks of vaccine adverse events need to be placed in the context of the “known benefits of COVID-19 and influenza vaccination in preventing COVID-19 and influenza disease and their potentially serious complications, including stroke.”

He added that the federal vaccine safety monitoring systems are designed to be sensitive and indications of issues such as these are evidence that the process is working.