The Covid vaccines developed by Pfizer-BioNTech and Moderna may have a slight association with an increased risk of stroke when administered along with a high-dose flu vaccine, as per a recent analysis by the Food and Drug Administration (FDA). This risk is most evident in adults aged 85 and older, who usually receive the high-dose flu vaccine. However, the increase in risk appears to be very small, and it is possible that the risk may be related to the flu vaccine alone. Another analysis by the FDA indicates a small increase in the occurrence of seizures in children aged 2 to 5 after Covid vaccinations. These studies have not been peer-reviewed or published in scientific journals yet, but experts in vaccine safety have commended the studies.
It should be noted that neither study is definitive, and even if the associations are confirmed, the benefits of vaccination far outweigh the risks, especially in older adults. Both the flu and Covid infections themselves increase the risk of stroke. However, the findings suggest that further investigation is needed to fully understand these risks and ensure vaccine safety.
The FDA has not provided interviews with the researchers, but they have made the information available through the publication of these papers for transparency purposes. Both studies are based on observational data, which means that causality cannot be determined. The FDA plans to conduct a more robust study to explore the occurrence of seizures in children following vaccination.
Simultaneous administration of flu and Covid vaccines, or a combination vaccine, is increasingly being recommended by health officials to enhance vaccine uptake and simplify logistics. However, it is important to ensure the safety of this strategy.
Dr. Marco Cavaleri, who leads the office of biological health threats and vaccines strategy at the European Medicines Agency, is not yet convinced of the real increase in stroke risk. He highlights that strokes and related health issues are common in individuals aged 85 or older. Therefore, further investigation with larger datasets is required to clarify the situation.
US authorities initially raised concerns about a possible association between the Covid vaccines and stroke risk about a year ago. However, a more thorough investigation suggested that the link was highly unlikely, and other surveillance systems worldwide did not find any connections.
The recent study conducted by FDA and the Centers for Medicare and Medicaid Services analyzed stroke risk in over 5.4 million Medicare beneficiaries aged 65 and older. They examined the health records of those who received a Covid vaccine alone or with the flu vaccine between August 31 and November 6, 2022. The initial analysis did not find any statistically significant increases in stroke risk associated with the Covid vaccines administered alone. However, a breakdown by age revealed an increased stroke risk in individuals aged 85 or older who received the Pfizer-BioNTech vaccine and those aged 65 to 74 who received the Moderna vaccine. The association was most prominent when the Covid vaccine was given along with a high-dose flu vaccine or one containing an adjuvant.
Additional analysis of the relationship between the flu vaccine and stroke involved nearly 7 million Medicare participants who received a high-dose or adjuvanted flu vaccine. It showed a small but statistically significant increase of approximately 9 percent in stroke risk after receiving only the flu vaccine. This suggests that the high-dose flu vaccine itself may be responsible for the observed increase in strokes in the study.
Although these findings do not warrant changes to vaccine recommendations, they indicate the need for further investigation. The small number of additional strokes and seizures observed are not cause for alarm, especially considering that the diseases themselves also carry a risk of stroke. However, it is important to gather more data to ensure vaccine safety.