Neurology News

Does the Pfizer Bivalent COVID-19 Booster Up Stroke Risk in Older Adults?

The Pfizer bivalent COVID-19 booster is not associated with increased risk for ischemic stroke relative to the monovalent or Moderna bivalent COVID-19 vaccines, according to study findings published in NPJ Vaccines.

At the beginning of 2023, the United States (US) Centers for Disease Control and Prevention (CDC) announced that the Pfizer bivalent vaccine met the threshold for an ischemic stroke risk investigation.

To clarify whether the Pfizer bivalent booster is associated with a higher risk for ischemic stroke compared with other COVID-19 vaccines, researchers sourced data from the TriNetX database. Individuals aged 65 and older who received the Pfizer bivalent booster (n=110,667), monovalent booster (n=96,156), or Moderna bivalent booster (n=26,962) on or before August 2023 were included in this analysis. To balance for cohort differences, a propensity matching approach was used, for a final sample size of 79,036 individuals in each cohort for the Pfizer and monovalent comparison and of 26,962 individuals in each cohort for the Pfizer and Moderna comparison.

There was also significantly reduced hazard of IS encounter diagnosis in the Pfizer bivalent versus Moderna bivalent cohorts, but only at the 1–21 day period.

After matching, the Pfizer and monovalent cohorts comprised:

  • individuals mean age, 73.63 and 73.61,
  • 55.21% and 54.98% were women,
  • 74.73% and 75.3% were White, and
  • 3.06% and 2.94% had potential health hazards due to socioeconomic and psychosocial circumstances, respectively.

Compared with the monovalent booster, the Pfizer bivalent booster was associated with lower risk for ischemic stroke at 1 to 21 days (hazard ratio [HR], 0.54; 95% CI, 0.47-0.62) and at 22 to 42 days (HR, 0.62; 95% CI, 0.54-0.72). No group differences in risk for new stroke were observed at 1to 21 days (HR, 1.072; 95% CI, 0.690-1.667) or 22 to 42 days (HR, 1.248; 95% CI, 0.839-1.856).

Compared with the Moderna bivalent booster, the Pfizer booster associated with lower ischemic stroke risk at 1 to 21 days (HR, 0.75; 95% CI, 0.58-0.96) but not at 22 to 42 days (HR, 0.99; 95% CI, 0.78-1.28).

The major limitation of this study was that these cohorts were not a representative sample of the US.

“We observed a reduced hazard of IS [ischemic stroke] encounter diagnosis in the Pfizer bivalent cohort compared to the monovalent cohort, perhaps due to bivalent boosters providing stronger protection against severe COVID-19 infection and hospitalization than their monovalent counterparts. […] There was also significantly reduced hazard of IS encounter diagnosis in the Pfizer bivalent versus Moderna bivalent cohorts, but only at the 1–21 day period,” the researchers concluded.

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