Why the measles, mumps and rubella vaccine is combined

President Donald Trump wants the combined MMR vaccine that protects against measles, mumps and rubella, broken up into separate shots. 

Individual vaccines against measles, mumps and rubella are not currently available in the United States. The U.S. Centers for Disease Control and Prevention’s acting director called for manufacturers to develop separate shots and Health and Human Services Secretary Robert F. Kennedy Jr. said officials are evaluating the feasibility of separating the vaccines.

The MMR vaccine has been combined since 1971, and it would take years for separate vaccines to be tested and licensed in the U.S.

Trump’s repeated calls to "break up the MMR shot" and "take them separately" might have Americans wondering whether they can get separate shots and how and why the vaccines were ever combined. Here are some answers to common MMR vaccine questions. 

Q: Why is the MMR vaccine combined, anyway? 

A: Public health officials wanted to make it easier for people to get vaccinated, because that increases overall vaccination rates and decreases cases of these diseases. 

Measles, mumps and rubella vaccines were good candidates for combination because they were typically given on the same schedule. Combining them meant fewer doctor’s visits and fewer needles in arms, which can be stressful for kids and parents. 

Combining the vaccines was also possible because all three rely on weakened versions of the viruses to trigger immune responses that teach the body to fight the live viruses, said Dr. Walter Orenstein, an epidemiologist who directed the U.S. Immunization Program from 1998 to 2004.

These vaccines had similar ingredients and manufacturing processes, which made it possible to combine them, Orenstein said.

Scientists rigorously tested whether these vaccines could safely and effectively be combined without reducing the immune responses to each individual illness.

The MMR vaccine is administered in two doses and given to children first at 12 to 15 months old and then between ages 4 and 6. Getting your child fully vaccinated against these three diseases requires two visits to your pediatrician’s office and two shots.

If the MMR vaccine were split up and you wanted to get your child vaccinated at separate medical appointments — something Trump has also advised — it could take six visits. That means scheduling six appointments, paying for six doctor visits and your child receiving six injections. 

When it is difficult to get fully vaccinated, fewer people do it. 

"If you’re separating the vaccine, there’s an inconvenience," said Dr. Amesh Adalja, an infectious disease expert at the Johns Hopkins Center for Health Security. "It’s also more likely that one or more of those vaccines slips through the cracks."

Q: Does any science support separating the MMR vaccine? 

A: No. 

"There is no published scientific evidence showing any benefit in separating the combination MMR vaccine," Johns Hopkins Bloomberg School of Public Health posted Oct. 8 on Facebook. Other vaccine experts echoed this sentiment. 

The White House provided no studies or reports that support separating the MMR vaccine into three vaccines. 

Vials of the MMR measles mumps and rubella virus vaccine sit in a refrigerator with other medicine Feb. 25, 2025, in Lubbock, Texas. (AP)

Q: Are other vaccines combined? 

A: Yes. The DTaP vaccine series protects against diphtheria, tetanus and pertussis or whooping cough. Like the MMR vaccine, separate vaccines aren’t available in the U.S. for diphtheria, tetanus and pertussis. 

The Pediarix vaccine protects against diphtheria, tetanus, pertussis, hepatitis B and polio and the Pentacel vaccine protects against diphtheria, tetanus, polio and Haemophilus influenzae type b or Hib. 

Q: If combination vaccines are intended to improve convenience, why aren’t all vaccines combined? 

A: In a perfect world, all the vaccine protection a person needs could be delivered in one combined shot, Adalja said. 

That’s not possible because physicians administer vaccines when the protection will be most valuable. 

"The vaccine schedule is not created arbitrarily," he said. "There’s different times (of life) when you might be exposed to something, different times when the risk for severe disease is higher."

It’s also impossible to combine certain vaccines.

Some ingredients in inactivated vaccines — or vaccines that use a killed version of a germ to prompt immune response — could kill the weakened live viruses used in the measles, mumps and rubella vaccines, Orenstein said. 

Lead medical assistant Maria Teresa Diocales administers the measles, mumps and rubella (MMR) vaccine to 1-year-old at International Community Health Services, Sept. 10, 2025, in Seattle. (AP)

Q: Do separate MMR vaccines exist anywhere? 

A: No country’s government recommends using three separate vaccines to protect against measles, mumps and rubella, but separate vaccines are available in some countries for use in certain circumstances, according to the United Kingdom government. 

In France, infants 6 months to 11 months can be given a separate measles vaccine if necessary following an exposure to measles or ahead of plans to travel somewhere with high numbers of measles cases. After that, however, French public health experts still recommend children receive a combined MMR vaccination following the vaccine schedule.  

Japan recommends a combined measles and rubella vaccine and does not routinely vaccinate against mumps, but a separate mumps vaccine is available. 

Q: Can separate vaccines be tested and licensed for use in the U.S.? 

A: If it could be done at all, it would likely take years to accomplish, experts said. 

"It would depend upon what regulatory requirements the (Food and Drug Administration) placed on the company in order to prove safety and efficacy of that vaccine," Adalja said. 

In May, a Department of Health and Human Services spokesperson told The Washington Post that all new vaccines would be required to "undergo safety testing in placebo-controlled trials prior to licensure." 

That raises ethical issues when it comes to clinical testing of individual vaccines against measles, mumps and rubella. 

Oversight boards that review and approve clinical trials would not approve trials with placebo groups for measles, mumps and rubella because an existing vaccine is effective, said Angela Rasmussen, a virologist at the University of Saskatchewan. 

Exposing children to potentially deadly illnesses is unethical, she said. 

There’s also no guarantee that vaccine manufacturers would even attempt to separate the vaccines. 

"Vaccines are not very lucrative, and they’re becoming less and less lucrative based on the environment that we have in the United States," Adalja said. 

Merck and GSK manufacture combined MMR vaccines used in the U.S. GSK did not respond to PolitiFact’s questions about whether they will respond to the administration’s calls to separate the MMR vaccine.

In a statement to PolitiFact, Merck said splitting the MMR vaccine would essentially involve creating three new, experimental and separately licensed vaccines, each requiring full clinical testing and regulatory review. 

"We estimate that, in total, it could take more than 10 years before Merck could obtain FDA approvals and begin manufacturing and commercialization," the company said.

A sign is seen outside a clinic with the South Plains Public Health District, Feb. 23, 2025, in Brownfield, Texas. (AP)

Q: What would happen if the combined MMR vaccine were no longer offered in the U.S.?

A: The most immediate effect would be that vaccination would stop because there is no alternative. But even if separate measles, mumps and rubella vaccines were eventually tested, approved and available, vaccine uptake likely would drop because getting vaccinated would require more effort, Rasmussen said. 

Either way, that would mean more cases of measles, rubella and mumps. 

"We will see more longer term impacts too," she said. That might include increased infertility from mumps, increased disability from measles and congenital rubella syndrome, more stillbirths and miscarriages from rubella and more cases of SSPE, a progressive brain disorder that stems from measles infection. 

Replacing the MMR vaccine with separate vaccines "is a preventable tragedy and terrible mistake for public health," Rasmussen said. 

Editor’s note: Google Translate was used throughout the research of this story to translate websites and statements into English.

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