This article, about splitting the MMR vaccine into its three components, was written by Dorit Rubinstein Reiss, Professor of Law at the University of California Law, San Francisco, who is a frequent contributor to this and many other websites, providing in-depth and intellectually stimulating articles about vaccines, medical issues, social policy, and the law.

Professor Reiss writes extensively about the social and legal aspects of vaccination in law journals. Reiss is also a member of the Parent Advisory Board of Voices for Vaccines. This parent-led organization supports and advocates for on-time vaccination and the reduction of vaccine-preventable diseases. She is also a member of the Vaccines Working Group on Ethics and Policy.

On August 10, 2026, President Trump issued an Executive Order supporting several of Secretary Kennedy’s anti-vaccine priorities, including Secretary Kennedy’s problematic paring down of the vaccine schedule, calling for splitting the MMR vaccine into individual shots for measles, mumps, and rubella, replacing aluminum adjuvants, and having the DOJ target states that require vaccines. I address that executive order here. This post focuses on splitting the MMR vaccine into its component shots, and explaining why this is much harder than it seems.

It’s also a really bad idea. 

Splitting the MMR vaccine is hard, time-consuming, and maybe impossible

It is going to be hard for US companies to get individual vaccines, measles, mumps, and rubella, back to market. 

The first MMR vaccine in the United States, made by Merck, was licensed in 1971. The current vaccine, MMR II, was approved in 1978, with a change to the rubella component.  In 2022, the FDA approved, and ACIP recommended a second MMR, Priorix, made by GSK.

The separate vaccines in the MMR shot are not available in the United States, and have not been for a while. In 1998, ACIP addressed it and voted for the combined vaccines – at that point, single vaccines were still available, but the combination was considered preferable. 

I have asked and was told that Merck has not continued to submit annual reports for the individual components of MMR. Currently, there are no licensed individual measles, mumps, or rubella vaccines in the United States. Only MMR and MMRV. 

What needs to happen for licensing? The individual vaccines will have to meet the requirements of clinical trials the FDA imposes and, for a biologics license application, which is what is required for a vaccine, the manufacturing site will also need to be licensed.

Now, there are clinical trials for the individual components from the 1960s; but the trials accepted by the FDA then were smaller than trials required for more modern vaccines, and I am not sure the FDA will accept these very old trials as sufficient. The trials required for the measles and rubella vaccines were in the hundreds.

The mumps trial was larger – over 6000 children. Modern trials are often larger – consider the rotavirus vaccine, with almost 70,000 infants, or the HPV vaccine, with 12,000 women. Further, if HHS Secretary Robert F Kennedy Jr is serious in his claim that these older vaccines were not sufficiently tested, he would – for consistency – direct the FDA to require new trials. New trials cost hundreds of millions of dollars or more. Why would companies do them? Where is the benefit to them? 

Even if the companies were willing, they would have to recruit, say, 10,000 people who would agree to let their one-year-old babies be randomized to getting the vaccines separately or in combination. Reminder: parents who want separate shots would not be guaranteed them in such a trial. Parents who want a single MMR would not be guaranteed it, either. Recruiting for that trial may not be fast or easy, and the trial itself would take time. 

If FDA is looking to smooth the path, it may accept the old trials as sufficient – but there is the question of the production line. Again, for a biologics license, the facility where it is produced needs to be inspected and licensed.  There are no facilities licensed currently to produce these individual vaccines. So first, a company has to want to manufacture these vaccines – and it’s not clear any would.

Then, the facility needs to be prepared and licensed. This is part of the Biologics License Application (BLA) submission, so the application cannot be filed until there is an FDA-inspected facility ready to produce it. Setting up such a facility is not trivial (though certainly possible), and getting it approved takes time. Only then can the application for a biologic license application (BLA) be fully submitted.  

For the entire BLA, the standard review process once submitted takes about 10 months, according to the FDA, and even an expedited review takes about six months. This is not something that can be done quickly – and again, there would have to be a company to undertake it. Again, the FDA can work to shorten it, but it’s not a quick and easy thing. 

It is not clear that relicensing the vaccines in the United States is practical, and at the least, it should take time and money – if you want people to be able to trust that the new vaccine is safe. 

What about getting vaccines from abroad? Some countries make individual vaccines for measles, mumps, or rubella. Individual vaccines are currently available from India, for measles from Indonesia, for mumps from China, and for mumps/rubella from Japan.  

Can they be licensed in the United States? Well, maybe. Historically, FDA’s requirements are higher than most other countries; the usual situation is that a vaccine is licensed elsewhere and additional data – more trials – need to be done before it’s licensed in the United States. 

Of course, the Kennedy/Trump FDA can relax the requirements and make it easy for these vaccines to be licensed in the United States. But at what cost? First, if Kennedy and Trump are worried about vaccine safety, then a more lax testing regime means more safety risks. Second, given the “America First” tenor of some of the administration’s comments, how would supporters feel about vaccines made in countries that the administration has derided in the past, and how would this work with an emphasis on production in the United States?

It might be possible, but it won’t be easy.

Splitting the MMR vaccine is a bad idea

Going back to the Administration’s drawing inspiration from Denmark, it, like other European countries, uses combination vaccines. Combination vaccines mean fewer needles; and if you’re worried about vaccine ingredients, they also generally mean fewer ingredients.

The volume of the vaccine is generally the same. As explained in ACIP’s 1998 discussion: “Each dose of the combined or monovalent vaccines contains approximately 0.3 milligrams of human albumin, 25 micrograms of neomycin, 14.5 milligrams of sorbitol, and 14.5 milligrams of hydrolyzed gelatin (Merck & Co., Inc., manufacturer’s package insert).” It is ironic that Kennedy – who likes to demonize vaccine ingredients – wants more of them. 

Further, President Trump’s view that giving individual vaccines at different times is better is misguided – and again, not what our peers do. First, who pays for the doctor visits? Many parents will not be able to afford more doctor visits – both in terms of medical fees and of the time off work. Access will be a real problem. 

Second, we know that people do not always come back – not for second doses, and not for other vaccines. 

Third, why would anyone want more needles in their kids’ bodies rather than less? Less pain is better for a child. And having shots spaced out does not reduce the child’s stress.

So what is the benefit? We will end with fewer children vaccinated against all three diseases – measles, mumps, and rubella – no safety benefit, more costs, and more pain. It’s a bad policy.

Finally, we know from other countries that splitting the MMR vaccine increases outbreaks of these diseases.

Conclusion

In short, splitting the MMR vaccine into individual measles, mumps, and rubella vaccines in the United States is somewhere between a non-starter and a serious, costly, and difficult undertaking. There are very few benefits, along with many drawbacks.