Claim: The 2026 US measles surge is being spread by vaccinated children, not unvaccinated ones

The claim that the 2026 US measles surge is being spread by vaccinated children is false. Data from reputable sources, including the CDC and Stanford Medicine, indicate that the majority of measles cases are occurring among unvaccinated individuals. Specifically, around 92% of cases are linked to unvaccinated or unknown-status individuals, while only a small fraction is among fully vaccinated people. This aligns with expert consensus on vaccine efficacy and outbreak dynamics. Opposing views are not supported by current evidence, which consistently highlights unvaccinated individuals as the primary drivers of the outbreak. The models diverge sharply — treat this as higher-uncertainty. Gemini comes in highest (50%), while Perplexity is lowest (0%). OpenAI expresses higher confidence than Gemini on this claim. There are no significant opposing claims in the evidence provided that would alter the verdict. The evidence overwhelmingly supports the notion that unvaccinated individuals are responsible for the majority of measles cases during the 2026 surge. While some may argue about the role of vaccinated individuals in transmission, the data clearly shows that they constitute a minor percentage of cases. This lack of substantial counter-evidence reinforces the conclusion that the claim is false.