Senator Ron Johnson (R-Wisconsin) on Monday disclosed internal records indicating that officials within the Biden administration detected a statistically significant signal for ischemic stroke in elderly individuals who received the Pfizer-BioNTech COVID-19 bivalent booster. This detection reportedly occurred as early as November 2022. Despite these findings, federal health agencies continued to recommend widespread booster use for seniors aged 65 and older.
The disclosure included nearly 2,000 pages of documents and a letter from Senator Johnson to Health and Human Services (HHS) Secretary Robert F. Kennedy Jr. The accompanying letter detailed internal communications and outlined a timeline of events surrounding the stroke signal.
According to the records, a draft communications plan from the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) regarding the booster was revised by the White House in January 2023. Language within the draft describing the stroke risk was reportedly altered from "moderately elevated" to "slightly elevated." Furthermore, mentions of "potential risk" were removed from the document, as reported by the Santa Clarita Valley Signal. An internal email from a CDC official, cited in the documents, noted, "Edits reflected from the [White House]. They don’t want to see this document again," suggesting direct White House involvement in the messaging changes.
Critics, including Senator Johnson, argue that these edits served to downplay legitimate safety concerns while federal health agencies simultaneously continued to promote high booster uptake among the elderly population. Johnson's office highlighted that public statements from health officials maintained there was "no change recommended in COVID-19 vaccination practice," even as officials were conducting detailed analyses, including a specific initiative termed the "Stroke Project," to evaluate the identified safety signal. This project reportedly continued through at least September 2025.
Senator Johnson stated, "From the initial detection of the safety signal in late 2022 … through at least September 2024, health officials continued to say the vaccine was safe while simultaneously searching for evidence to support that assertion." This statement underscores his concerns about the gap between internal investigations and public messaging.
The CDC initially identified the signal through its Vaccine Safety Datalink (VSD) system. The method involved comparing stroke rates within 21 days following vaccination to rates observed in the 22- to 42-day period post-vaccination. Officials noted that this specific signal did not appear in other vaccine monitoring systems, nor had it been detected internationally.
In response to the initial findings, a joint statement from the CDC and FDA affirmed their commitment to transparency, stating, "Although the totality of the data currently suggests that it is very unlikely that the signal in VSD represents a true clinical risk, we believe it is important to share this information with the public." The agencies consistently maintained that there was no evidence of an increased stroke risk directly attributable to the Pfizer bivalent booster, reiterating its safety for elderly recipients.
Subsequent detailed analyses conducted by federal researchers indicated that the elevated stroke signal was primarily observed among elderly patients who received an influenza vaccine on the same day as a Pfizer bivalent COVID-19 booster. In this specific cohort, 40 strokes occurred within 21 days of co-administration, compared with 20 strokes observed in the 22- to 42-day period. For individuals who received only the Pfizer booster, 60 strokes were recorded in the initial 21 days, closely followed by 58 strokes in the subsequent 22- to 42-day period, suggesting a more consistent rate without the co-administration of a flu vaccine.
Based on these findings, FDA researchers concluded that the increased risk of stroke was more likely linked to high-dose or adjuvanted influenza vaccines, rather than the COVID-19 booster itself. Despite this conclusion, federal guidance continued to recommend COVID-19 vaccination for nearly all Americans aged six months and older, including guidance for co-administration with flu vaccines.
Senator Johnson criticized this ongoing approach, asserting, "As safety signals for ischemic stroke appeared, Biden HHS officials continued to urge people to get vaccinated, jeopardizing the health of millions of Americans." His letter to HHS Secretary Kennedy Jr. requested additional records pertaining to the stroke detection, including detailed information about the CDC’s "Stroke Project" and interviews with officials involved in vaccine safety monitoring. Johnson emphasized that key documents remain unreleased, leading to continued uncertainty regarding the full extent of HHS awareness and decision-making during this period.
