A quick-reference library of common vaccine claims. Each entry gives a short evidence status and links to a fuller explanation where available.
Large, high-quality studies and repeated WHO reviews have not found a causal relationship between vaccines and autism. WHO’s 2025 review again reaffirmed that conclusion.
Read the evidence →The claim arose from a 1998 paper that was later retracted. Subsequent large studies and reviews have not found that MMR causes autism.
Read the evidence →Thiomersal contains ethylmercury, which is processed differently from methylmercury. WHO reviews have not found evidence that thiomersal in vaccines causes autism or other neurodevelopmental disorders.
Read the evidence →Aluminium salts are used as adjuvants in some vaccines. WHO states that current evidence, including large cohort data, does not support a link between aluminium-containing vaccines and autism.
Read the evidence →Yellow Card reports record suspected reactions. A report can identify a potential safety signal, but it does not by itself establish causation.
Read the evidence →Safety monitoring continues after authorisation. Regulators use spontaneous reports, healthcare databases, studies and international surveillance to investigate possible signals.
Read the evidence →WHO’s safety committee reviewed the concern and concluded that available data do not support a causal association between HPV vaccination and infertility or primary ovarian insufficiency.
Read the evidence →Timing alone cannot establish causation. Investigators compare background rates, timing, biological plausibility and findings from other studies before deciding whether a causal relationship is likely.
Read the evidence →Preventive interventions do not need to eliminate every infection to reduce disease burden. Vaccine effectiveness varies by vaccine, outcome, population and time since vaccination.
Read the evidence →Yes. Like other medicines, vaccines can cause side effects. Most listed effects are mild and short-lived, while serious reactions can occur rarely. The relevant question is the size and certainty of each risk compared with expected benefits.
Read the evidence →A safety signal is a reason to investigate. Regulators assess whether the observed pattern exceeds what would normally be expected and whether other evidence supports causation.
Read the evidence →HPV vaccines do not contain infectious HPV capable of causing HPV infection. They use components designed to trigger an immune response against selected HPV types.
Read the evidence →Report totals do not provide an incidence rate without a suitable exposure denominator, background rates and causality assessment.
Read the evidence →Regulators also use clinical trials, healthcare databases, analytical studies, international information and expert review.
Read the evidence →Trial size and follow-up limit which uncommon or delayed events can be detected before authorisation. Post-authorisation monitoring continues in larger populations.
Read the evidence →Different designs answer different questions and have different vulnerabilities to bias and confounding.
Read the guide →Statistical significance does not by itself establish causation, practical importance or freedom from bias.
Read the explanation →Study quality and relevance matter, but one result should normally be interpreted within the wider body of evidence rather than treated as decisive in isolation.
Read the guide →Consensus is a broad conclusion formed from repeated assessment of the evidence. It does not require unanimity and can change when important evidence changes.
Read the New Reader Guide →Evidence can support a conclusion while uncertainty remains. The appropriate question is how strong, precise and consistent the evidence is.
Read the guide →