Do vaccines cause cancer?

The verdict

No. There is no evidence that vaccines cause cancer.

The evidence runs the other way. Two vaccines in routine use prevent cancers, by preventing the infections that cause them. That is the part of this subject worth your attention.

What the evidence shows

Start with what is actually established. NCI states that certain infectious agents, including viruses, bacteria, and parasites, can cause cancer or raise the risk of it. Some viruses disrupt the signaling that keeps cell growth in check. Some infections weaken the immune system.

Two of those infections can be prevented with a vaccine.

Human papillomavirus is the first. NCI states that infection with high-risk HPV types causes nearly all cervical cancers, along with most anal cancers and many oropharyngeal, vaginal, vulvar, and penile cancers.

Hepatitis B is the second. NCI states that chronic infection with hepatitis B or hepatitis C can cause liver cancer, and notes that infants in the United States and most other countries have been routinely vaccinated against hepatitis B since the 1980s.

How well the HPV vaccine works

NCI's account is specific. Clinical trials showed the vaccines are highly effective at preventing HPV infections at multiple sites in both men and women. Protection is greatest when given before first exposure to the virus, though adults still benefit.

Beyond preventing infection and precancer, NCI notes that real-world data now show the vaccine greatly reduces the incidence of cancer. Protection against the targeted HPV types has so far been found to last more than a decade.

On safety, NCI is equally direct. More than two decades of safety monitoring show the vaccines have caused no serious side effects. The most common problems have been brief soreness and other local symptoms at the injection site, similar to other vaccines.

Where the confusion comes from

Three things get tangled together.

The first is timing. Vaccines are given to almost everyone, and cancer is common. Any two common things will co-occur often. That is coincidence, not cause.

The second is a real historical episode. Polio vaccines made in monkey kidney cell cultures between 1955 and 1963 were contaminated with a virus called SV40. A published review in Oncogene reports that up to 30 percent of US polio vaccines were affected, and that a meta-analysis of five studies did not support the idea that SV40 exposure raised overall cancer incidence or cancer mortality. That was a manufacturing problem of that era, and it was investigated for decades. It is not a statement about vaccines in general.

The third is a misreading of how vaccines work. A vaccine teaches the immune system to recognize a target. It does not alter the growth-control genes in your cells, which is what cancer requires. Our page on what cancer is explains that mechanism.

What the vaccines cannot do

Being accurate cuts both ways, and overstating the benefit is its own problem.

NCI notes that the HPV vaccine will not clear an existing HPV infection and does not treat an abnormal Pap result. It protects against types not yet acquired.

Vaccination also does not replace screening. People who have been vaccinated still follow the cervical screening schedule, because the vaccine does not cover every cancer-causing type. Our page on cancer screening covers why both are needed.

What to actually do

• Ask about HPV vaccination for children at ages 11 or 12. NCI notes it can start at 9, and is recommended through age 26 for people not adequately vaccinated earlier.
• Check whether you had the hepatitis B series. Adults at increased risk who were never vaccinated should ask about it.
• Keep to your cervical screening schedule regardless of vaccination status.
• Bring specific claims you have read to a clinician rather than judging them alone. Ask what the evidence behind a claim actually is.

Where to take a real concern

If you have had a reaction to a vaccine, that is a medical matter and deserves attention on its own terms. Report it and discuss it with a clinician. It is a separate question from whether vaccines cause cancer, and treating them as one question helps nobody.

If someone shows you a study claiming a link, two questions do most of the work. Was it a randomized trial or a population study, or a laboratory finding in cells? And has anyone replicated it? A single unreplicated result is a lead, not a conclusion. Our page on cancer risk factors covers how established causes are actually identified.

What this does not mean

• No vaccine is free of side effects. Sore arms, brief fevers, and rare allergic reactions are real and documented.
• "No evidence of a link" is a statement about the evidence, which is extensive here, spanning more than two decades of monitoring.
• HPV and hepatitis B vaccines prevent specific cancers. They do not prevent cancer in general.
• Nothing here is advice about your own vaccination schedule, which is a conversation with your clinician.

Sources

• NCI: HPV Vaccine Fact Sheet
• NCI: Infectious Agents and Cancer
• NCI: Common Cancer Myths and Misconceptions
• FDA: Gardasil 9
• Dang-Tan T, et al. Polio vaccines, Simian Virus 40, and human cancer. Oncogene 2004 — abstract via NCBI E-utilities

How this page was made

An AI-assisted editorial system helped prepare this page. This article has not been reviewed by a healthcare professional unless a named reviewer is specifically shown. Cancer Explained is published by the National Cancer Information Foundation as a nonprofit-oriented public-interest education project. It is not a diagnostic service, does not recommend treatments, and is not for emergencies.

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