Skip to content
Home » The bivalent COVID vaccines are not linked to strokes

The bivalent COVID vaccines are not linked to strokes

Last updated on August 15th, 2023 at 01:07 pm

The anti-vaccine world has jumped on some safety signals that seem to indicate that the bivalent COVID vaccines are linked to strokes. This group has shown how it misuses preliminary data to try to make false claims about every vaccine, especially the COVID-19 vaccines. This leads to false claims about these vaccines.

This post is going to examine what was found on VAERS, what is a safety signal, and what the FDA and CDC did to determine that there was no link between the bivalent COVID-19 vaccines and stroke. Even though this link has been dismissed, you just know that the anti-vaccine world will push it for the next few months.

Photo by Artem Podrez on

About the safety signal

The FDA and CDC reported that an early safety signal for increased risk of ischemic stroke was detected in older adults who received the Pfizer-BioNTech bivalent COVID-19 vaccine. According to the agencies, the incidence of ischemic stroke in the CDC’s Vaccine Safety Datalink (VSD) among individuals 65 and up in the 21 days following vaccination with Pfizer’s bivalent booster “met the statistical criteria to prompt additional investigation” when compared with the 22-44 days thereafter.

The VSD is a large database of medical data which includes vaccination histories, health outcomes, and subject characteristics. The VSD database contains data compiled from surveillance on more than seven million people in the United States, including about 500,000 children from birth through age six years.

Let’s clarify what is meant by a safety signal. Anti-vaxxers want to believe that it represents a causal link between the vaccine and the signal. But it’s not.

Safety signals are observations of a potential adverse event that are reported in any of the vaccine safety databases. If a safety signal is observed, then scientists need to determine if there is a causal link between the vaccine and the signal, or if it is just coincidental. There are several ways to do this:

  1. Check other vaccine databases to determine if they show the same safety signal.
  2. Compare the incidence to a non-vaccinated or general population. For example, researchers could compare the incidence of ischemic strokes after receiving bivalent COVID-19 vaccines from the VSD database and compare it to the incidence for the same age group in the general population.
  3. Perform a case-control or cohort study to accurately compare the incidence of ischemic stroke in unvaccinated and vaccinated cohorts. This takes the longest amount of time, which could be problematic if it’s a serious adverse event. Eventually, these types of studies will be completed within a year, because this type of study will be the most accurate in determining a potential causal link.

So, it’s important to note that a safety signal does not imply either correlation or causation. Further studies are required to determine if there is a link.

Bivalent COVID-19 vaccines are not linked to strokes

However, further analyses of the Vaccine Adverse Events Reporting System (VAERS), the Centers for Medicare & Medicaid Services database, and a preliminary study of the Veterans Affairs database found no safety signals and no increased risk of stroke with either Pfizer or Moderna’s bivalent vaccines. Moreover, Pfizer-BioNTech’s global safety database detected no safety signals for ischemic stroke with their bivalent vaccine. And vaccine surveillance systems in other countries also have not reported any safety signals for ischemic stroke.

The CDC and FDA concluded that:

Often these safety systems detect signals that could be due to factors other than the vaccine itself. All signals require further investigation and confirmation from formal epidemiologic studies. When one system detects a signal, the other safety monitoring systems are checked to validate whether the signal represents an actual concern with the vaccine or if it can be determined to be of no clinical relevance.

The CDC and FDA also noted that confounders, that is, variables that cause a spurious association between a cause and effect, may have contributed to the safety signal observed in the VSD database.

Although it appears that there is no evidence that this safety signal does infer a causal link between the bivalent COVID-19 vaccines and ischemic stroke, that does not mean that the CDC and FDA (along with other countries’ monitoring systems) will stop looking.

Observing safety signals does not mean that there is a link between a vaccine and an adverse — I cannot repeat that enough. It is a signal for the CDC and FDA to go looking harder to confirm or refute the suspected link. Both agencies went looking and found nothing.

So, as of this date, there is no link between the bivalent COVID-19 vaccines and ischemic stroke.

Michael Simpson

Don’t miss each new article!

We don’t spam! Read our privacy policy for more info.

Liked it? Take a second to support Michael Simpson on Patreon!
Become a patron at Patreon!