Quick answer (TL;DR): About 1 in 8 new cancers worldwide in 2024, roughly 2.3 million cases, were linked to infections, according to a new analysis by the International Agency for Research on Cancer (IARC). Five infections (H. pylori, HPV, hepatitis B, Epstein-Barr virus and hepatitis C) account for nearly all of them, and vaccination, screening and treatment can prevent many of these cancers.
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What did the new study find?
The analysis was carried out by IARC, the cancer agency of the World Health Organization (WHO), and published in The Lancet Oncology on 28 September 2026. It estimates that about 2.3 million new cancer cases worldwide in 2024, or 12% of all new cases, were attributed to infections with viruses, bacteria or parasites. The researchers say many of these cancers could be prevented with tools that already exist: vaccination, screening, and testing and treatment of the infections themselves.
The study covered 12 infections that are already established as causes of cancer in humans. According to IARC, the burden was highest in Eastern Asia, Sub-Saharan Africa, Central and Eastern Europe, and South-East Asia.
Which five infections are behind most of these cases?
Five infections account for nearly all of the infection-linked cases. H. pylori and HPV alone were behind roughly 1.5 million cases in 2024.
| Infection | Approx. cases in 2024 | Main cancers | Key prevention |
|---|---|---|---|
| Helicobacter pylori (H. pylori) | 760,000 | Mainly stomach (gastric) cancer | Testing and antibiotic treatment |
| Human papillomavirus (HPV) | 750,000 | Mostly cervical cancer; also anal, vulvar, vaginal, penile and some head and neck cancers | HPV vaccination and cervical screening |
| Hepatitis B virus | 360,000 | Mostly liver cancer | Vaccination and antiviral treatment |
| Epstein-Barr virus (EBV) | 260,000 | Mainly nasopharyngeal cancer and Hodgkin lymphoma; some gastric cancers | No widely available vaccine |
| Hepatitis C virus | 160,000 | Mostly liver cancer | Testing and antiviral treatment |
How can an infection lead to cancer?
An infection does not cause cancer overnight. Certain long-term infections can quietly damage cells over many years, and in some people that slow, cumulative damage eventually leads to cancer. This is why prevention works on a long timeline: treating or vaccinating against the infection can interrupt the process long before cancer develops. Most people who have these infections never develop cancer.
Which of these cancers can be prevented?
Unlike many cancer risk factors, these infections have known countermeasures:
- Vaccines: HPV and hepatitis B vaccines are among the most effective tools we have, and they work best when given before exposure.
- Testing and treatment: H. pylori can be detected with simple tests and treated with antibiotics. Chronic hepatitis B and C have antiviral treatments that lower the risk of liver cancer.
- Screening: Cervical screening catches HPV-related changes early, when they are most treatable.
- Preventing transmission: IARC also points to measures such as safe injection practices.
The IARC authors say policymakers should prioritize scaling up these proven interventions. For another example of disease prevention through vaccination, see our World Polio Day 2026 guide.
Does the HPV vaccine affect fertility?
From my community health work: One worry I have come across is that HPV vaccination in teenage girls could cause infertility or problems having children later. It tends to spread at first among some parents and people with limited or no formal education, when a new vaccine reaches a community. It is an understandable worry, and it deserves a clear answer.
What the evidence says: The concern traces back to a small number of individual case reports since 2012 that linked HPV vaccination to premature ovarian insufficiency, a condition in which the ovaries stop working normally before age 40. WHO's Global Advisory Committee on Vaccine Safety reviewed the evidence in 2019, including case reports, surveillance data and epidemiological studies, and concluded that the available data do not support an association between HPV vaccination and infertility. WHO describes the vaccine's safety profile as extremely favorable.
Preventing cervical cancer also helps protect future fertility, because treatments for cervical cancer, such as surgery or radiation, can affect a woman's ability to have children. If you are a parent with this worry, ask the health worker or doctor offering the vaccine.
Why do some students faint after vaccination at school?
From my community health work: After vaccination in some schools, one or two girls faint or feel dizzy because of fear or anxiety. Seeing this can frighten other students and parents, and some then become unwilling to have the vaccine.
What the evidence says: WHO calls these events immunization stress-related responses. They usually happen within the first 15 minutes after the injection and mostly involve school-age children. The term is used because such responses are not specific to vaccines: they come from fear, pain or the stress of the injection process, not from the vaccine itself. Fainting can happen after any vaccine, and a faint is not a sign that a vaccine is unsafe.
The main risk is getting hurt in a fall. A few simple steps help:
- Eat normally and drink water before the vaccination.
- Tell the vaccinator if you have fainted before or feel dizzy or very nervous.
- Sit or lie down for the injection, and stay seated for about 15 minutes afterwards.
- If someone feels faint, lie them down or sit them with their head lowered, and keep calm. Seeing a calm response helps other students feel calm too.
- Get urgent medical help for trouble breathing, swelling of the face or lips, or if a person does not recover quickly.
What can this study not tell us?
- It estimates shares across whole populations, not the risk for any one person.
- It relies on cancer data from each country, and the availability and accuracy of that data vary.
- It counted only infections already established as cancer-causing, so the total effect of infections may be underestimated.
What can you do?
- Ask a doctor whether HPV and hepatitis B vaccination are right for you or your children.
- If you or your child tends to feel faint around injections, tell the vaccinator beforehand.
- If you have an ulcer or persistent upper stomach pain, ask about testing for H. pylori.
- Follow the cancer screening advice that applies to your age and local health guidance.
- Keep up the basics: not smoking, a balanced diet and regular physical activity.
Frequently Asked Questions
If I get one of these infections, will I get cancer?
No. Most infections never lead to cancer. The study estimates population-level shares, not individual risk. Cancer develops in some people after years of persistent infection. If you have symptoms or concerns, talk to a clinician rather than trying to assess your own risk.
What should I ask my doctor about?
HPV vaccination, hepatitis B vaccination, and testing or treatment for H. pylori if you have persistent stomach symptoms are the topics most often highlighted. Which of these apply to you depends on your age, history and local health guidance, so a clinician can advise on what fits your situation.
Does the HPV vaccine cause infertility?
No. WHO's Global Advisory Committee on Vaccine Safety reviewed the evidence in 2019 and concluded that the available data do not support an association between HPV vaccination and infertility. Parents who are worried can ask the health worker or doctor offering the vaccine.
Is it normal for a student to faint after a vaccine?
Fainting around injections is common, especially in school-age children and adolescents. It is usually a stress response to fear, pain or the injection process, not a reaction to the vaccine itself, and it can happen with any vaccine. The main risk is injury from a fall, which is why students should sit or lie down and wait about 15 minutes after the injection. Get urgent medical help for trouble breathing, swelling of the face or lips, or if a person does not recover quickly.
Do infections cause most cancers?
No. About 1 in 8 new cancer cases in 2024 (12%) were attributed to infections in the IARC analysis. Most cancers have other causes, such as tobacco use, alcohol, diet, inactivity and genetics.
Is there a vaccine against these infections?
There are vaccines against HPV and hepatitis B, and they are among the most effective tools for preventing infection-related cancers. There is no vaccine against H. pylori or hepatitis C, but both can be tested for and treated, and there is no widely available vaccine for Epstein-Barr virus. A doctor can advise which vaccines suit your age and local schedule.
Do the usual healthy habits still matter?
Yes. Infection prevention adds to established steps, such as not smoking, a balanced diet, regular physical activity and recommended cancer screenings. It does not replace them.
Sources
- International Agency for Research on Cancer: Global burden of cancer attributable to infections in 2024, Questions and Answers (September 2026)
- The Lancet Oncology (2026): Global burden of cancer attributable to infections in 2024, a worldwide incidence analysis
- World Health Organization, Global Advisory Committee on Vaccine Safety: Human papillomavirus vaccines and infertility
- World Health Organization, Global Advisory Committee on Vaccine Safety: Immunization stress-related responses
- World Health Organization: Cervical cancer fact sheet
- World Health Organization: Hepatitis B fact sheet
General information only, not medical, healthcare, or psychological advice. Check current medical guidelines with a certified physician or licensed healthcare provider before acting on anything published here. Never disregard professional medical advice or delay seeking it because of something you read on this site.
