Claim linking Pfizer COVID-19 vaccine, cancer in mouse distorts study | Fact check

The claim: New study proves Pfizer COVID-19 vaccine causes cancer

An Aug. 20 Instagram post (direct link, archive link) shows two dissected mice with their inner organs exposed.

“SHOCKING: New Study proves Pfizer mRNA induced turbo cancer,” the post reads.

The post received more than 1,000 likes in nine days. A similar post shared on X, formerly Twitter, in July was reshared more than 10,000 times.

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Our rating: False

There is no evidence that COVID-19 vaccines cause cancer. The post distorts a case report focused on a mouse that died of lymphoma after it was given a second dose of the Pfizer COVID-19 vaccine during a study. The report did not claim the two events were causally linked.

Report finds evidence of causality ‘lacking’

The Instagram post references a case report published in Frontiers in Oncology in May that examined a study involving 14 mice injected with the Pfizer COVID-19 vaccine. The case report focused on one mouse in the study that died of lymphoma, a cancer of the lymphatic system, two days after receiving its second dose of the vaccine.

But the report does not assert this event “proves” the mouse developed cancer because of the vaccine, as the Instagram post claims.

In fact, the report states evidence to make such a determination is “lacking” and that a causal link between the two events “cannot be unequivocally established and may represent coincidence.”

There are also several problems with the study that make the claim faulty, Dr. David Gorski, a professor of surgery and oncology at Wayne State University, told USA TODAY.

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First, the vaccine doses given to the mice were between 480 and 600 times the size of those typically given to humans when accounting for body weight, Gorski wrote in a blog post that also debunked the claim.

Another problem stems from the way the vaccine was given, Gorski said. Humans receive it as a shot into a muscle. But the report detailed how the vaccine was injected directly into the mice’s tail veins in the study, which Gorski said gives the vaccine a direct path to the animals’ heart and lungs.

“If it’s injected into the muscle, most of the vaccine stays in a relatively small area. It doesn’t really go very far,” Gorski told USA TODAY. “If you inject it into the bloodstream, it’s in the bloodstream – it’s going everywhere. … Nothing like what is done in real life.”

The study also tracked the body weights of the mice. Roughly a week before it received the vaccine, the mouse that died prematurely began losing weight – a key indicator of illness in mice. And the particular breed of mouse used in the study is known to spontaneously develop cancers, specifically lymphomas, Gorski said.

“That leads me to think the mouse probably had cancer before,” he said.

There is no evidence that the COVID-19 vaccines cause cancer, according to the National Cancer Institute.

The post shared on X is from the account for the 2022 film “Died Suddenly,” which promotes baseless claims about the COVID-19 vaccines. Far-right conspiracy theorist Stew Peters produced the film.

USA TODAY has debunked other inaccurate claims promoted by Peters, including the false claims that the COVID-19 vaccine is made from snake venom and that the war in Ukraine is fabricated.

USA TODAY reached out to Peters and to the social media user who shared the post but did not receive responses from either.

Health Feedback also debunked the claim.

Our fact-check sources:

• Frontiers in Oncology, May 1, B-cell lymphoblastic lymphoma following intravenous BNT162b2 mRNA booster in a BALB/c mouse: A case report

• David Gorski, Aug. 28, Phone interview with USA TODAY

• Respectful Insolence, July 12, A mouse “died suddenly” of “turbo cancer” after COVID-19 vaccination

• National Cancer Institute, Aug. 1, COVID-19 Vaccines and People with Cancer

• Boston University, July 11, Humane Endpoints

• National Library of Medicine, January 1983, Immunomorphologic classification of spontaneous lymphoid cell neoplasms occurring in female BALB/c mice

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This article originally appeared on USA TODAY: Post falsely links Pfizer COVID-19 vaccine, mouse cancer | Fact check