COVID vaccines don't cause cancer. But false claims persist in sea of misinformation

A health worker administers a dose of COVID-19 vaccine during a vaccination clinic in Reading, Pa. on Friday, Oct. 7, 2022. THE CANADIAN PRESS/AP-Matt Rourke

Anyone who spends even a moderate amount of time online has likely come across social media posts falsely claiming that COVID-19 vaccines are harmful to human health.

Among the most widely debunked claims is that vaccines developed with messenger RNA technology can cause cancer because they contain “monkey virus DNA."

Such claims were even repeated during a U.S. congressional hearing on vaccine injuries last year, but North American and European health authorities have stressed that there is no proof of a causal link between COVID vaccines and cancer, or that mRNA vaccines can alter human DNA in any way.

A senior policy analyst with the Canadian Cancer Society also debunked such claims while noting the added harm of false beliefs is that they can derail the deployment of proven therapies.

“Misinformation can increase vaccine hesitancy and can delay the provision of health care,” Apiramy Jeyapalan said in an emailed statement.

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The fact that cancer patients and others may still be exposed to that kind of misinformation online and elsewhere is very concerning and shouldn’t be ignored by the medical and scientific community, says a Canadian scientist whose areas of expertise include health literacy.

Cheryl Peters, a senior scientist at BC Cancer and the BC Centre for Disease Control, said going through cancer treatment is “a highly vulnerable time," especially for patients who are feeling overwhelmed and may be susceptible to information from dubious sources. 

“We have to be aware that these things are circulating and be aware that our friends and family could be getting exposed to these conspiracy theories that might really actually materially harm them if they listen to them,” Peters said. 

She noted that people who spread vaccine misinformation online attribute all sorts of things – from heart attacks to sudden deaths – to COVID shots. So when it comes to false claims, for example, that the vaccines are also the reason younger age groups are seeing higher rates of certain types of cancer than previously, “your Spidey senses should go up.”

“There's no sort of one exposure to something — whether it be a vaccine or other (things) — that's going to be able to cause every single kind of negative health outcome. That's just not how our biology works,” Peters said. 

Dr. Aaron Schimmer, director of research at the Princess Margaret Cancer Centre in Toronto, said he believes the level of misinformation surrounding COVID vaccines has decreased over time, but acknowledged that false claims still creep up. 

“I think a number of patients, especially around the time when the vaccines were introduced, if they were newly diagnosed with cancer around that time … would say, ‘Well, you know, my cancer was caused by the vaccine.’ Of course, again, biologically that's not true. Those cancers have been there probably growing slowly (over) many years,” he said. 

Schimmer, who mainly treats leukemia in his clinical practice, said none of his own patients have raised specific conspiracy theories about vaccines and cancer, “but I've definitely had patients who've had concerns about the vaccine, the safety and questions as to whether the vaccine was the trigger for their cancer.”

The irony, Schimmer said, is that mRNA vaccines were being tested as potential cancer treatment long before the COVID pandemic hit. The idea is that mRNA could train an individual's immune system to target specific cancer cells. 

“It was the investments that were being made at the time to understand how these may work as cancer treatments that actually allowed us to generate a COVID vaccine so quickly,” he said. 

Peters, the BC Cancer scientist, said mRNA vaccines have great value and there is promising work to be done with them in the future. But she wonders if the science behind that is being properly translated and communicated to the masses.

“That's a bit of an existential question for science in general, I think,” she said. 

Samara Perez, a clinical psychologist in the psychosocial oncology department of McGill University Health Centre in Montreal, says the vast majority of patients consider doctors and health-care professionals to be the most trusted sources of information, and research over the years has backed that up. 

Even though a cancer diagnosis can set off a range of psychological responses, such as depression and anxiety, Perez does not believe a particular vulnerability to misinformation is among them. 

“I think people that are susceptible to misinformation prior to (getting) cancer would be the same after," said Perez, who is also a professor at McGill University, noting that she debunks any cancer myths raised by her patients "right away."

Both Schimmer and Peters said there’s nothing wrong with a healthy dose of skepticism when it comes to making personal medical choices. Peters said she also understands why some patients – especially those from historically marginalized communities – distrust the system. 

But that’s where doctors, scientists and health-care authorities have to step up and ensure that they are being upfront about the rare, but real, vaccine side-effects and other potential negative outcomes, she said, noting that transparency goes a long way toward building trust. 

A study co-authored by Peters and published earlier this year found that Canadians were better at identifying known cancer risk factors, such as tobacco use, than recognizing cancer myths. 

For example, more than half of survey respondents incorrectly believed that stress and consuming additives increases cancer risk. Between 20 and 30 per cent believed risk is increased by wearing deodorant, using hair dye, living near power lines and "having bad luck." But the vast majority of respondents did not believe that vaccination, in general, is a risk factor. 

Peters believes that myths and misinformation now play a bigger role in health-care choices people make than in the past because “we all have basically unlimited access to information” – and some people are intentionally peddling false claims online so they can profit from unproven "remedies."

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“And that, I think, is not a problem that's going away,” Peters added. “Cancer patients and other people with chronic conditions really need support.”

The Canadian Cancer Society advises people to approach unverified sources of information with caution. On its website, the society aims to dispel some common myths – such as the belief that certain foods can prevent or cure cancer – and urges people who have questions or are unsure about something to call its cancer information helpline. 

“For people with cancer, talk to your health-care team about which of the approved COVID-19 vaccines is right for you, and to determine the best timing of the doses based on your unique circumstance," the society said in a statement.

This report by The Canadian Press was first published March 23, 2024.