COVID-19 vaccines not associated with stroke risk, study finds
Concomitant vaccination against COVID-19 and influenza was associated with a very small increase in stroke risk, likely driven by the flu vaccine, according to the analysis of more than 5 million vaccinated Medicare beneficiaries.
Two recent studies provided data on questions regarding COVID-19 vaccination.
The first, published by JAMA on March 19, assessed whether vaccination was associated with strokes among older patients. It was a retrospective analysis of more than 5 million Medicare beneficiaries who received either brand of the COVID-19 bivalent mRNA vaccines, 11,001 of whom subsequently had a stroke. The study period was Aug. 31, 2022, through Feb. 4, 2023, and stroke rates were compared during 1 to 21 days and 22 to 42 days after vaccination versus a control window of 43 to 90 days afterward. There were no statistically significant associations between the COVID-19 vaccines and nonhemorrhagic stroke, transient ischemic attack, or hemorrhagic stroke in the early windows versus the later window. However, there were inconsistent associations between concomitant administration of COVID-19 and flu vaccines, with Pfizer plus flu vaccine associated with nonhemorrhagic stroke during the 22- to 42-day window and Moderna plus flu vaccine associated with transient ischemic attack during the 1- to 21-day window.
Flu vaccination alone was also associated with a small increase in stroke, which "suggests that the observed association between vaccination and stroke in the concomitant subgroup was likely driven by a high-dose or adjuvanted influenza vaccination," said the study authors, who noted that the implications of this finding are limited by the study not including analysis of the consequences of unvaccinated patients becoming infected with influenza. "The clinical significance of the risk of stroke after vaccination must be carefully considered together with the significant benefits of receiving an influenza vaccination," they wrote. An accompanying editorial said that the results provide "reassurance about the COVID-19 boosters" and suggest that the flu vaccine could be associated with one to three cerebrovascular events per 100,000 vaccinated patients, which would be outweighed by vaccine benefits on a public health level, but "some healthy older adults who are at an extremely low risk of serious influenza complications may not find the individual risk-to-benefit calculus favorable."
The other study, published by Annals of Internal Medicine on March 26, evaluated the effectiveness of annual COVID-19 vaccination with a booster for high-risk groups. Using data on incidence of COVID-19 in the U.S. and related hospitalizations, deaths, and health care costs, the study found it would be optimal for children younger than two years and adults ages 50 years or older to receive a booster dose five months after an annual vaccination against COVID-19. The booster would result in 123,869 fewer hospitalizations (95% uncertainty interval [UI], 121,994 to 125,742) and 5,524 fewer deaths (95% UI, 5434 to 5613), averting approximately $3.6 billion in costs. Limitations include that the calculations did not consider nonpharmaceutical interventions or pre-existing vaccine-acquired immunity, the study authors said. They noted that this study was conducted to analyze a vaccination schedule under consideration by the FDA and that the results indicate "adopting an annual vaccination campaign with the provision of a second dose to children younger than 2 years and adults aged 50 years or older can be a suitable approach to protect individuals against SARS-CoV-2 infection and associated outcomes."