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FDA: Getting COVID vaccine alongside flu shot may raise risk of stroke

By CM Chaney · October 27, 2023

In brief…

  • FDA analyses link COVID+flu vaccine to small stroke increase in seniors over 85
  • But risk very small compared to strokes from COVID infection
  • Another study flagged potential seizure rise in young kids after COVID shots
  • Link disappeared when compared to high 2022 infection rates
  • Experts say benefits of shots still outweigh risks, advise spacing doses
FDA analyses suggest the COVID vaccine may increase stroke risk slightly when paired with high-dose flu shots in seniors over 85, while another study indicated a potential seizure link in young children that requires more data.  NIAID / Wikimedia

The COVID vaccine may be linked to a small increase in stroke risk when given with a high-dose flu shot, primarily in seniors over 85, according to new FDA analyses.

The agency said the Pfizer and Moderna bivalent boosters showed the strongest association when administered alongside Fluzone, a high-dose flu vaccine for older adults. But the risk remains very small, at about 3 strokes per 100,000 doses.

For comparison, the 2022 COVID death rate for over-85s was over 1,200 per 100,000, with experts saying vaccination still outweighs the risk.

It’s the second analysis linking strokes in seniors to the vaccine combo. Another flagged a potential seizure increase in young kids after COVID shots. Both studies were observational and cannot prove causation.

Scientists theorize vaccines may stress blood pressure and arteries or prompt severe inflammation affecting blood flow. Those getting high-dose flu and Moderna shots had a 35% higher mini-stroke risk; with Pfizer, a 20% increase.

Further analysis suggested the flu vaccine alone raises stroke risk around 9% in seniors. So it may drive the effect, not the COVID boosters.

Still, the absolute risk after both shots was low - 3.1 extra strokes per 100,000 Pfizer doses, 3.3 for Moderna. COVID infection brings a much higher stroke risk.

Mitigation could include spacing shots and using different arms. President Biden has urged flu shots in one arm, COVID in the other.

The pediatric analysis found a tentative seizure link in young kids after Pfizer and Moderna shots. But it disappeared when compared to 2022’s high infection rates, suggesting unrelated fevers.

Most seizures occurred with fevers, expected with shots. Experts say infections clearly raise seizure risk in kids more than vaccines.