Vaccines are safe and effective
Vaccines prevent diseases that can cause disability and death. Their benefits are supported by trials and large studies. Serious side effects are rare, and the balance depends on the vaccine, age and health of the person receiving it.
On this page
Vaccines prevent serious disease
A major review found about 95% protection against measles after one MMR dose. Long-term HPV studies found substantially less cervical cancer when vaccination began before exposure. Hepatitis B vaccination in infancy also reduced later liver cancer in a long-term trial. These are different vaccines and outcomes, not one universal success rate.
Safety and side effects
A favorable benefit–risk balance does not mean zero side effects. Fever-related seizures can follow MMR, and mRNA COVID vaccines can rarely cause myocarditis. The vaccine, age, health and dose matter. The linked pages explain those risks directly.
Specific concerns have specific evidence
Large studies do not support a causal link with autism. Ingredients and childhood schedules have also been studied. No single study tests every combination and every possible delayed effect; the answer comes from several kinds of evidence.
The vaccine type matters
Injectable inactivated polio vaccine cannot cause poliovirus infection. Live oral polio vaccines have rare paralysis risks, and vaccine-descended virus can sometimes circulate and cause outbreaks. These real risks should not be transferred to a different vaccine or denied.
Vaccines prevent diseases that can cause disability and death.
Keep in mind
- The findings apply to the vaccines, populations and outcomes studied. Personal recommendations depend on your health and current local guidance.
Find the answer you need
Sources you can check
Publication links open in a new tab, so you can keep your place here.
Vaccines for measles, mumps, rubella, and varicella in children (opens in a new tab)
Cochrane, 2021
Reviews effectiveness and harms in children. Different outcomes use different studies and participant totals.
Return to reading ↑What are the benefits and risks of different human papillomavirus (HPV) vaccines for preventing cervical cancer and other HPV-related disease? (opens in a new tab)
Cochrane, 2025
Outcome-specific evidence: the whole review population is not the infertility sample. Cervical-cancer benefit is a relative reduction.
Return to reading ↑Long-term efficacy of neonatal hepatitis B vaccination against hepatocellular carcinoma and other liver diseases: a 30-year follow-up study of the Qidong hepatitis B intervention study (opens in a new tab)
PLOS Medicine, 2014
Cluster-randomized trial in high-endemicity China; not a birth-versus-two-months trial in low-risk US infants.
Return to reading ↑Measles, Mumps, Rubella (MMR) Vaccine Safety (opens in a new tab)
CDC
Explains known MMR side effects; combined MMRV has a different seizure-risk comparison.
Return to reading ↑FDA Approves Required Updated Warning in Labeling of mRNA COVID-19 Vaccines Regarding Myocarditis and Pericarditis (opens in a new tab)
FDA, June 2025
Observed 2023–24-formulation incidence in days 1–7 is not an excess-risk estimate. Persistent MRI findings have uncertain long-term meaning.
Return to reading ↑Statement of the WHO Global Advisory Committee on Vaccine Safety (GACVS) on vaccines and autism (opens in a new tab)
WHO, 2025
Assesses vaccine–autism evidence, including thimerosal and aluminum; this is not a finding of zero vaccine side effects.
Return to reading ↑The Childhood Immunization Schedule and Safety: Stakeholder Concerns, Scientific Evidence, and Future Studies (opens in a new tab)
Institute of Medicine, 2013
Reviews schedule safety methods and evidence gaps; does not validate every future schedule.
Return to reading ↑Poliomyelitis (opens in a new tab)
WHO
Distinguishes inactivated injectable vaccine from live oral vaccine and its genuine rare risks.
Return to reading ↑
Detailed research notes and source data
Our longer notes explain how we checked the studies, including disagreements and documents we could not get.
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These pages have not completed expert review. For personal vaccine advice, talk to a clinician who knows your circumstances.
Research checked: . Wording reviewed: 2026-10-15. Version: vaccine-2026-10-15.
We revisit the page when new evidence or corrections change the answer. A public history of corrections is not available yet.