Fact Check-No evidence that Pfizer’s COVID-19 vaccine causes Alzheimer’s disease

As of this article’s publication, the COVID-19 vaccine manufactured by Pfizer-BioNTech has not been shown to cause Prion diseases or neurodegenerative diseases such as Alzheimer’s and Lou Gehrig’s disease (ALS). Experts say a paper circulating online does not provide legitimate evidence otherwise.

In late April 2021, conservative outlets such as The Gateway Pundit (here) and National File (here) published stories on a paper linking Pfizer’s vaccine for the novel coronavirus to neurodegenerative diseases. Facebook posts sharing screenshots from these outlets can be seen here and here .

Titled “COVID-19 RNA Based Vaccines and the Risk of Prion Disease,” the paper in question, published in a journal called ‘Microbiology and Infectious Diseases’ in January, was authored by “J. Bart Classen, MD.”

Classen has, over several years, published papers and articles opposing the use of vaccines (here) and his work has been shared by vaccine sceptics such as Robert F. Kennedy Jr. (here).

The paper’s central claim is that Pfizer’s mRNA vaccine “contains sequences believed to induce TDP-43 and FUS to aggregate in their prion-based conformation leading to the development of common neurodegerative [sic] diseases.” In other words, he says certain "letters" in RNA code in the vaccine have the potential to trigger changes to the way particular human proteins (namely TDP-43 and FUS) fold, making them cause disease (here).

According to experts consulted by Reuters, as of this fact check’s publication, evidence does not support this claim.

A Pfizer spokesperson said: “There is no evidence” when asked by Reuters whether its mRNA COVID-19 vaccine had the potential to lead to Alzheimer’s and other neurodegenerative diseases.

The Pfizer-BioNTech COVID-19 vaccine uses new messenger RNA (mRNA) technology, which contains brief genetic instructions for human cells to temporarily manufacture proteins that mimic a small part of the novel coronavirus. The presence of those viral proteins spurs the immune system into action. No actual virus is contained in the vaccines (here).

Prions are misfolded brain proteins that can cause mad cow disease or bovine spongiform encephalopathy, Creutzfeldt Jakob disease, or CJD, chronic wasting disease in deer and elk, and scrapie in sheep (here).

These infective agents are also a rare but important cause of dementia, and scientists say the process involved in these diseases - in which prion proteins change shape and stick together to form polymers that damage the brain - is also what happens in common dementias such as Alzheimer’s, and in Parkinson’s and other neurodegenerative diseases (here).

Alzheimer’s is the most common form of dementia, in which patients progressively lose their ability to think and care for themselves. Current drugs only treat symptoms (here).

Amyotrophic lateral sclerosis (ALS), commonly known as Lou Gehrig’s disease, is a rare neurologic disorder mainly affecting the nerve cells responsible for controlling voluntary muscle movement such as walking or talking. It has no cure, and gets worse over time until it eventually leads to death, most often from respiratory failure (here).

Having reviewed the paper, which is less than three pages long and provides only three sentences describing its methodology, Dr Albert Hofman, a clinical epidemiologist at the Harvard T.H. Chan School of Public Health (here), told Reuters by phone that the paper provides no evidence for the author’s findings, which he described as “untenable.”

Hofman also stressed that those at greater risk of developing Alzheimer’s, namely individuals over 60, are also at greater risk of becoming seriously ill with COVID-19. Their vaccine need is therefore most urgent, he said, echoing the U.S. Centers for Disease Control and Prevention (CDC)’s statements (here).

According to the U.S. Alzheimer’s Association, currently available COVID-19 vaccines are safe for those living with Alzheimer’s and other dementias (here).

Dr Irina Skylar-Scott, a neurologist at Stanford Hospitals and Clinics who specializes in Alzheimer’s and other disorders of cognition and behavior (, told Reuters by phone that Classen’s claims were “overreaching to say the least,” noting that neither TDP-43 nor FUS, the two proteins he discusses, are associated with Alzheimer’s disease.

Skylar-Scott said she knew of no evidence linking any of the COVID-19 vaccines to Alzheimer’s, and emphasized that Alzheimer’s patients are particularly vulnerable to the novel coronavirus because the infection may put their cognition at risk.

“Once they become ill, they don’t recover always to their prior mental baseline,” Skylar-Scott said of Alzheimer’s patients, a high-risk population she said would benefit from COVID-19 vaccination.

As for ALS, the ALS Association says on its website that it continues to consult with ALS medical specialists nationwide and remains “encouraged by the safety and efficacy data” of the vaccines thus far (here).

Citing data from the U.S. Department of Veterans Affairs showing veterans with ALS are three times more likely to die of COVID-19 than veterans without ALS, a Feb. 4 letter from the ALS Association to the U.S. Department of Health says “people with ALS should receive the COVID-19 vaccine at the earliest possible phase” (here).

“ALS takes away the ability to walk, speak, swallow and, eventually, to breathe. Most people with ALS die from respiratory failure, a circumstance that is severely exacerbated by COVID’s respiratory effects,” the letter reads.

Dr Brian Appleby, a neurologist at the Case Western Reserve University School of Medicine who specializes in both prion disease and Alzheimer’s (here), told Reuters by phone that there is no evidence mRNA vaccines cause neurodegenerative diseases, and that the journal article in question uses the term prion disease “quite loosely” to refer to other protein misfolding disorders.

“In isolation, it seems to be speculative,” Appleby said, noting that there was “no experimental model per se associated with the study” and that there is “certainly no data from the vaccine makers that this is a concern.”

The U.S. Food and Drug Administration’s briefing documents for both the Pfizer vaccine (here) and the Moderna vaccine (here), which also uses mRNA technology, do not mention anything about the development of neurodegenerative diseases during clinical trials that involved tens of thousands of volunteers.

A CDC spokesperson told Reuters via email that it “is aware of no evidence to date that vaccination contributes to the development of prion-related disease or neurodegenerative diseases like ALS and Alzheimer’s.”

It is worth noting that the last paragraph of Classen’s paper says: “Many have raised the warning that the current epidemic of COVID-19 is actually the result of an [sic] bio-weapons attack released in part by individuals in the United States government,” while citing two sources authored by Classen himself. The same claim has been espoused by larger “plandemic” conspiracy theories that Reuters has debunked here , here and here .

As reported here by USA Today, Classen proposed in 1999 that the influenza vaccine caused type 1 diabetes (here), a claim disproved by the Johns Hopkins Institute for Vaccine Safety here .

When reached for comment via email, Classen told Reuters: “You should leave the scientific criticism to scientists” (which Reuters has done throughout this article) and that Reuters was “not qualified to criticize my work.” He did not provide further evidence or comment on his paper’s findings.

Reuters reached out to both Microbiology and Infectious Diseases and SciVision, the paper’s journal and publisher, respectively, for comment but did not receive a response.

“It’s hard to believe this paper stood up to the peer-review process,” Dr David Irani, a professor of neurology at the University of Michigan Medical School (here), told Reuters via email.

Echoing Appleby, Irani said that the paper’s author “provides no detail regarding how his analyses were conducted and no actual data for his readers to evaluate for themselves.”

Irani noted that the paper was “rife with ambiguous phrases such as ‘may cause’ and ‘the potential to’ that heighten its speculative tone,” describing the discussion as “straying into areas that are completely unfounded” as Classen “heavily references his own prior publications in a way that identifies him as an anti-vaccine advocate rather than an objective scientific investigator.”

“Experience over the last 9 months has certainly taught us that mRNA vaccines against COVID-19 can cause side effects in some individuals, but there is absolutely no evidence linking them to neurodegenerative disease,” Irani concluded.


False. As of this article’s publication, there is no evidence that mRNA COVID-19 vaccines lead to prion disease, Alzheimer’s, or ALS.

This article was produced by the Reuters Fact Check team. Read more about our work to fact-check social media posts here .