What the CDC and FDA Disclosed

Let's summarize the critical points from their announcement. Due to the extensive administration of the updated Covid-19 bivalent mRNA vaccine, the CDC's Vaccine Safety Datalink (VSD) conducted further analysis on vaccine safety, focusing specifically on ischemic stroke in individuals aged 65 and older.

The CDC acknowledged that this demographic exhibited a higher likelihood of experiencing an ischemic stroke within 21 days following vaccination compared to 22-42 days after receiving the Pfizer bivalent vaccine. However, this risk was not observed with the Moderna bivalent vaccine.

Assuring the public, the CDC stated that other surveillance systems—including the Centers for Medicare and Medicaid Services database, the Veterans Affairs database, and the Vaccine Adverse Event Reporting System (VAERS)—did not detect this stroke signal. Consequently, the CDC recommended maintaining current vaccination practices.

"Although the totality of the data currently suggests that it is very unlikely that the signal in VSD represents a true clinical risk," the CDC noted, "we believe it is essential to share this information with the public, as we have in the past, when one of our safety monitoring systems detects a signal."

The CDC and FDA committed to ongoing monitoring of the situation, intending to share further data at the FDA's Vaccines and Related Biological Products Advisory Committee meeting on January 26.

Recent Developments from the FDA Meeting

Following the three-week period, the FDA released meeting slides. The session began with an overview of the bivalent mRNA booster, first administered in the U.S. in September 2022. By January 11, 2023, approximately 49.5 million doses had been given to individuals over five years old, including 21.4 million doses to those over 65.

Dr. Nicola Klein, a vaccinology expert at Kaiser Permanente, led the preliminary analysis of ischemic stroke occurrences following Pfizer's bivalent mRNA vaccination within the VSD.

Established in 1990, the VSD is a collaborative project between the CDC and various healthcare organizations, encompassing the electronic health records of roughly 12.5 million individuals across the U.S.

Dr. Klein utilized concurrent vaccinated comparators to assess the risk of ischemic stroke between 1-21 days and 22-42 days post-vaccination. This approach aimed to ensure that recently vaccinated individuals were more comparable to current vaccinees than to those who were unvaccinated, thereby minimizing potential confounding factors such as genetics and behavior. All analyses were adjusted for age, sex, race or ethnicity, VSD site, calendar time, and seasonality.

The analysis revealed a 1.47 times (47%) increased risk of ischemic stroke in the 1-21 day period compared to the 22-42 day period after receiving Pfizer's bivalent mRNA vaccine. This risk was statistically significant (p = .005), with a 95% confidence interval ranging from 1.11 to 1.95, indicating an increase in risk at the extremes of the distribution.

The analysis indicated that the signal for increased stroke risk persisted but gradually diminished over the following seven weeks, with a peak increase occurring between 11-22 days post-vaccination.

A review of 22 cases of post-bivalent mRNA vaccine strokes showed that the median age was 77.5 years, with none having a prior history of stroke. Interestingly, 23% had previously contracted SARS-CoV-2, though only one had a recent infection within the last six months.

Dr. Klein's research also indicated that co-vaccination with the high-dose or adjuvanted influenza vaccine resulted in a two-fold increase in stroke risk during the first 21 days compared to the 22-42 day period. However, no significant differences in stroke risk were observed when comparing the bivalent mRNA vaccine alone, standard-dose influenza vaccination, or influenza vaccination on its own.

These findings suggest that strong immune responses from the combination of the bivalent mRNA and high-dose or adjuvanted influenza vaccines may heighten stroke risk, while using a standard-dose influenza vaccine appears to mitigate this risk.

Dr. Klein recommended continued surveillance of stroke risks following bivalent mRNA vaccination across various systems, while still endorsing the vaccine for eligible individuals. However, it may be prudent for those aged 65 and older to refrain from receiving the high-dose or adjuvanted influenza vaccine on the same day as the bivalent mRNA vaccine booster, as this combination might overly stimulate the immune system and potentially contribute to stroke.

What Additional Research Indicates

The CDC's assertion that no stroke signal was detected in other countries may not be entirely accurate. It's possible they referred specifically to the bivalent mRNA vaccine, which may be valid. However, some countries have reported increased stroke risk linked to the monovalent mRNA vaccine.

In a semi-systematic review of extensive safety surveillance studies on Pfizer's mRNA vaccine conducted last July, I outlined key investigations into rare adverse events associated with the vaccine. These studies, primarily from the U.S., U.K., Denmark, and Israel, involved control groups and sample sizes exceeding 100,000 vaccine recipients.

While myocarditis was consistently associated with Pfizer's mRNA vaccine, findings regarding stroke risk were mixed, with some studies indicating significant increases, decreases, or no changes at all.

In a previous article, I analyzed these surveillance studies and concluded that robust studies revealed mixed signals concerning hemorrhagic stroke. However, evidence suggests a slight increase in ischemic stroke risk associated with Pfizer's mRNA vaccine.

A recent preprint study from Emory University explored the stroke risk following the initial Covid vaccination among 5 million vaccinees. They reported significantly increased risks of both ischemic and hemorrhagic strokes among those who contracted Covid within 21 days of vaccination.

Nevertheless, this study lacked a comparison of stroke risks from Covid alone, making it challenging to ascertain whether the stroke risks stemmed from the vaccination or the Covid infection.

In conclusion, while the mRNA vaccine does carry some risk of ischemic stroke, this risk appears to be contingent upon certain factors, such as co-vaccination with high-dose or adjuvanted influenza vaccines or co-infection with SARS-CoV-2.

Nonetheless, public perception may not reflect these nuanced findings, often leading to unfounded claims against Pfizer's mRNA vaccine. The consistency of trends observed in various studies remains crucial for understanding these associations.

As further research is warranted to clarify the relationship between mRNA vaccines, influenza vaccines, Covid disease, and stroke, it may be prudent to delay the simultaneous administration of the Covid bivalent mRNA vaccine and high-dose or adjuvanted influenza vaccines until more definitive answers emerge.

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