The MMR vaccine has been studied in more than 23 million children across six decades, much of that work funded by the…

The MMR vaccine has been studied in more than 23 million children across six decades, much of that work funded by the department @SecKennedy now runs. Last night on CNN he told American parents it is hard to determine whether it is safe. He is lying. Here is the evidence. 🧵

Acyn@Acyn · Aug 15, 2026

Michaelson: But you said MMR is safe? RFK JR: What I said is it's hard for us to make a determination of safety without look of relative safety. Michaelson: The CDC says they are safe. RFK JR: It's hard for anybody to declare something safe without safety studies

2/ Published this summer in the Pediatric Infectious Disease Journal by Burstain & colleagues: 2,560,035 American children, drawn from a national records database spanning more than 1,800 US hospitals, followed to age 8. Children who received MMR before age two had no increased risk of autism. Hazard ratio 0.97, 99% CI 0.91 to 1.03. The design answered the standard criticisms of past research. American kids on the American schedule. Children compared at identical ages. Confounders selected through formal causal diagrams, reaching back into the pregnancy record. Plus a built-in test for hidden bias, using a comparison vaccine (PCV) with no plausible link to autism. That test came back clean too. pubmed.ncbi.nlm.nih.gov/42520244/

3/ Annals of Internal Medicine, 2019: every child born in Denmark across twelve years. 657,461 children, including more than 31,000 who never received MMR at all. No increased risk of autism in vaccinated children; the hazard ratio was 0.93. The authors concluded the study strongly supports that MMR does not increase autism risk and does not trigger autism in susceptible children. acpjournals.org/doi/10.7326/M1…

4/ Parents who already have a child with autism sometimes hesitate on MMR for the younger sibling. That exact question has its own study. JAMA, 2015: 95,727 US children with older siblings, including 1,929 whose older sibling had autism, the highest-risk group there is. MMR was not associated with increased autism risk at any age, in either group. Among the highest-risk kids the estimates ran below one: relative risk 0.76 after one dose, 0.56 after two. jamanetwork.com/journals/jama/…

5/ Cochrane review, 2021, evidence graded by the strictest methods in medicine: 138 studies, more than 23 million children. The vaccines work against all three diseases, and the autism estimate came back at 0.93, if anything below one. The review also quantified the real side effects, because that is what safety studies do. A small short-term rise in febrile seizures, roughly one extra for every few thousand children vaccinated, frightening to watch and without lasting harm. A rare temporary drop in platelets, about one per 40,000, that usually resolves on its own. The risks are known, small, and counted. doi.org/10.1002/146518…

6/ In this same interview, the Secretary raised safety concerns about aluminum adjuvant in the MMR vaccine. There is no aluminum in the MMR vaccine. Not in 1971 when it was licensed, and not at any point since. It is a live attenuated vaccine; the weakened viruses generate the immune response on their own, so no adjuvant is needed. The ingredient list is on the FDA package insert. The nation's top health official is questioning the safety of an ingredient that is not in the product. fda.gov/media/75191/do…

7/ The backdrop, from this week's CDC update: 2,566 confirmed measles cases in the United States this year, with about a hundred new cases in each of the last two weeks, as kids go back to school. We passed 2025's full-year total weeks ago. 2025 was already the worst measles year since 1991. Two thirds of this year's cases are children and teens. This is the moment the Secretary chose to tell parents that the safety of the measles vaccine cannot be determined. cdc.gov/measles/data-r…

8/ In this same interview he called the measles vaccine the best way to prevent measles. His own agency's website, up right now, says getting the MMR vaccine is much safer than getting measles, mumps, or rubella, says that many carefully performed studies have found no link to autism, and says that no published scientific evidence supports separating it into three shots. The evidence is public. His own department publishes it. He has spent two decades being corrected on it. And during the worst measles year since 1991, he went on national television and told American parents it is hard to determine whether this vaccine is safe. That is a lie about the safety record of a childhood vaccine, told by the Secretary of Health and Human Services, in the middle of a national outbreak. It is morally abhorrent. Children will pay for it. cdc.gov/vaccine-safety…