When I saw that a neurologist had written a Wall Street Journal (WSJ) op-ed about the measles, mumps, and rubella (MMR) vaccine, my hopes lifted. Finally, I thought, someone with neurology training is going to tell readers what measles does to a child's brain. There's acute encephalitis in about one of every 1,000 cases, often leaving permanent damage behind. 

Subacute sclerosing panencephalitis, which surfaces seven to ten years later, takes apart a child's language and movement and is almost always fatal. And then there is immune amnesia, which erases a chunk of what a child's immune system has already learned and leaves them vulnerable again to infections they had beaten, and it can last for years.

That is not what the op-ed is about, however. The piece argues that the MMR vaccine should be split into three separate shots, and claims that the August 10 executive order’s recommendation to do so “fits with the science.” It goes further, writing that the order calls for splitting MMR "to reduce peak inflammation." The order never says that. It never mentions inflammation at all, resting instead on alignment with peer developed countries, parental choice, and a January 2026 HHS assessment, so the inflammation rationale is one the op-ed is supplying on the policy's behalf. 

My colleague Jake Scott has already taken apart the order itself, from the arithmetic behind the dose count to the fact that the products in question do not exist and would take Merck more than a decade to build. The push to split MMR has never had a mechanism behind it. Andrew Wakefield recommended separating the shots in 1998 on the strength of a study by him and his colleagues involving only 12 children that was later retracted for fraud, and most of what has followed has been assertion. 

The WSJ op-ed provides the mechanism and cites studies to support it. Those studies found that vaccination can trigger the first seizure in these children, but that it does not cause the underlying disease or change its course.  

The scientific core of the WSJ piece is that children with variants in SCN1A, a gene that codes for a sodium channel critical to normal neuron firing, had seizures and neurologic deterioration after vaccination. That much is true, and the story of how we figured it out is one of the better vindications of vaccine safety we have.

In 2006, Berkovic and colleagues looked for SCN1A variants in children with alleged vaccine encephalopathy because their symptoms resembled Dravet syndrome, a severe genetic epilepsy already known to be caused by SCN1A mutations in most cases. They tested 14 children and found SCN1A mutations in 11 of them, arising de novo in every case where the parents' DNA was available (meaning the mutation was new in that child rather than inherited). This confirmed that these children indeed had Dravet syndrome. 

Decades of studies had not found any harm from vaccines, yet they left families with many unanswered questions. That study did something different: It finally handed families an answer. Their child had a genetic condition. The vaccine hadn't caused it. 

Four years later, the same group asked whether vaccination changed the course of the disease and found that it did not. Vaccination can pull the first seizure earlier in a child who was already going to have one, but it does not alter intellectual outcome, seizure type, or trajectory, and the authors concluded that vaccination should not be withheld from these children. The WSJ op-ed concedes as much when it notes that the deterioration would have happened anyway from a cold or from measles itself, which is exactly what the 2010 study established. It cites the study’s premise (that the neurologic deterioration would have happened anyway) but not the conclusion.

The push to split MMR has never had a mechanism behind it.

Who would the policy of splitting MMR protect? Dravet syndrome occurs in about one in 15,700 US births, and because the great majority of these variants arise de novo, there is no family history to screen for and no way to identify these infants at the 12-month visit. For the children who are known to have Dravet syndrome, pediatric neurologists already manage that vulnerability directly, with individualized plans that can include antipyretics around vaccination and seizure rescue medication, and routine vaccination is still recommended for them. 

The op-ed extends the argument to variants in other genes (SCN1B, PMPCB, and GCDH) linked to conditions in which seizures or neurologic deterioration can be precipitated by fever or physiologic stress. But naming more genes still doesn’t show that combined MMR worsens their course, or that separating its components would prevent anything.

Fever and febrile seizures after MMR happen about one to two weeks out, and the Centers for Disease Control and Prevention (CDC) attributes most adverse events after MMR, fever included, to the measles component. Fever is one of the effects of the inflammatory response that the immune system mounts to the vaccine, the very thing the op-ed wants to reduce. Splitting MMR into three shots still means the child gets the measles component, which is responsible for most of the fever associated with MMR. 

The op-ed’s own justification is that splitting the doses would reduce “peak inflammation,” the theory that giving all three components in one shot produces a more concentrated immune and inflammatory response than spacing them out would. Peak inflammation isn't a standard measure. Researchers track particular inflammatory markers, and different ones peak at different times and different heights, so there's no single number the phrase refers to. Nobody has measured any of them for MMR against its separate components, which means there is no evidence the combination produces a higher peak, and no interval at which spacing would lower one.

The author tells readers that in 2019 he suggested the best approach was to continue vaccinating while finding ways to reduce unnecessary inflammation, particularly in susceptible children. What the 2019 piece actually says is that someday we may be able to identify at-risk newborns and prevent the fever and inflammation from colds and vaccinations from triggering deterioration. The next sentence notes that we don't yet know how to do that, and people should follow the recommendations and get vaccinated. A hypothetical about a subgroup nobody can currently identify has become a recommendation for every child in the country. 

The op-ed acknowledges that there's no evidence that reducing peak inflammation helps, then argues that the absence of evidence isn't the same as evidence against it. That's true, but it cuts both ways: the same absence means the theory was never established to begin with. Nothing in the piece shows that splitting MMR reduces the inflammatory response responsible for febrile seizures. The CDC's own page states that no published evidence shows any benefit to splitting MMR into three shots. 

Splitting MMR would delay when children are protected against all three diseases, and the effect of this delay has been measured. Vaccine Safety Datalink data show the relative incidence of seizures after a first MMR dose was more than twice as high at 16 to 23 months as at 12 to 15 months. To the extent that splitting pushes vaccination later, and the op-ed itself concedes that some children will not come back on schedule, the proposal could worsen the outcome it was written to prevent. Delay is the only part of this proposal anyone has studied, and the data show it makes seizures more likely, not less. 

The op-ed also argues that the CDC is wrong to downplay the long-term risk of these febrile seizures, but that claim doesn't hold either. A Danish cohort found no increased rate of epilepsy in children who had febrile seizures after MMR vaccination compared with children whose febrile seizures had other causes. And a 15-year US cohort study published in January found that no child went on to develop epilepsy after MMR receipt. 

How far apart should the three shots be given? The op-ed never says, and the answer decides whether there is anything here to study. If the three can be given at one visit, nothing about the peak inflammation has changed, and the rationale evaporates. If they have to be spaced, a two-dose MMR series could become as many as six vaccination encounters instead of two, and we are owed an interval, a measure of inflammation, and evidence that the interval moves it.

The op-ed does anticipate the obvious consequence, noting that some parents won't bring their children back for the extra shots, and then treats that as a convenience problem to be solved with pharmacy access and computerized records. 

Coverage falls when life happens and a shift changes, a sibling spikes a fever, the car doesn't start, or the co-pay lands in a bad week.

Centralized records do not make a parent return. Whether children come back is one of the outcomes by which a vaccination policy succeeds or fails, not a detail to be sorted out afterward. Getting a recommended vaccine into a child is a delivery problem before it is an immunology problem, which is why every additional visit gets counted as a chance to lose a child from the series rather than an inconvenience to be smoothed over. 

Coverage falls when life happens and a shift changes, a sibling spikes a fever, the car doesn't start, or the co-pay lands in a bad week. The families with the least slack absorb that first.

We have done this before, with an interval and data behind it. When post-licensure monitoring found that the MMRV vaccine (which also covers varicella, or chickenpox) roughly doubled febrile seizure risk compared with separate MMR and varicella shots in the week or two after the first dose, the CDC’s Advisory Committee on Immunization Practices did not wait for the full evidence review. 

It issued an interim recommendation that same month, February 2008, dropping the existing preference for MMRV, and updated the formal recommendations in June 2009 once its working group had finished the analysis. 

This is a system that has already changed direction when the evidence called for it, and it did so on a preliminary signal rather than waiting for certainty. The op-ed doesn’t mention that.  

The piece closes on trust, and this is where I think it does the most damage. Offering parents a choice sounds generous, but a choice offered without evidence behind it is not neutral, because when a clinician says the shots can be separated if you'd prefer, the parent hears that somebody has a reason to prefer it.

The same instinct shows up twice more, and both times it gives away that this was never really about MMR. The op-ed advises getting flu and COVID boosters a week apart rather than on the same day as pharmacies suggest, though CDC sets no waiting interval between them and studies have found co-administration to be safe. It also calls waiving human trials for COVID strain updates a far riskier proposition than splitting MMR, though it never says by what measure. 

The two aren’t comparable regulatory questions to begin with: Updating an antigen within an already-established platform is not the same undertaking as licensing three new standalone products. Underneath it all is an intuition that less immune stimulation at once must be better, and that intuition needs demonstrating before it can support anything else.

Three shots are not better than one.

And look at what this argument is being offered to support it. At the signing, President Trump called splitting up shots inconvenient but said he thought it would have "a huge impact on autism," a link hundreds of studies have failed to find, and described the volume going into a child as the size of a bottle of soda, when a visit with five injections comes to about half a teaspoon. 

Three shots are not better than one. They involve more injections, more visits, higher costs, more time spent incompletely protected while a family works through them, and no demonstrated benefit at the end of it.

That doesn’t sound like a gold standard recommendation to me.

Dr. Steier is a public health scientist and scientific communicator. She is the founder of Unbiased Science, an organization that uses data visualizations, real-world analogies, and human voice to communicate complex scientific concepts for public understanding via multiple media modalities.

The opinions voiced in CIDRAP Op-Ed pieces are the authors' own and do not necessarily represent the official position of CIDRAP.