After 100s of millions of safe MMR shots, Trump baselessly said the vaccine is possibly ‘quite lethal’

President Donald Trump said the combined vaccine for measles, mumps and rubella is potentially deadly. His evidence? He said he heard it, but didn’t say from whom.

During an Aug. 10 Oval Office event, Trump signed an executive order seeking to split up the combination MMR vaccine, which has been approved for use in the U.S. for about 55 years.

“We want it in three separate vaccinations, given at separate times,” Trump said. “Together, there could be a possibility they’re quite lethal and separately, uh, it looks like they are not at all lethal but just very effective.”

A reporter asked Trump if there was any evidence the combined vaccine for measles, mumps and rubella is “quite lethal.”

Trump replied: “No. What I’ve heard is that there are some people that say it is that way and I say, well, let’s say there’s a 5% chance of it, let’s split it up, let’s split it up.” 

He added, “I’ve heard when you put them together, they can be explosive.”

We asked the White House for evidence that it is possibly “quite lethal” and the statement we received from spokesperson Kush Desai did not answer that question. Desai said that Trump has “voiced questions and concerns” about the combined vaccine and wants to give parents options.

The president made his statement at a time when measles cases are rising and vaccination rates are dropping. 

Here’s how scientists concluded the vaccine is safe.

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Research shows the combined MMR is safe

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. It requires two visits to the pediatrician. If the MMR vaccine were split up, it could take six visits.

Requiring six visits rather than two, “would likely lead to drops in immunization coverage which could lead to major resurgences of the diseases,” Dr. Walter Orenstein, an epidemiologist who directed the U.S. Immunization Program from 1998 to 2004, told PolitiFact following Trump’s remarks.

Trump’s statement that the MMR is lethal contradicts longstanding scientific research and the conclusions of the U.S. Centers for Disease Control and Prevention that the combined MMR is safe — and safer than getting the deadly measles virus.

U.S. regulators approved the first combined MMR vaccine in 1971 following extensive clinical testing to ensure it was safe and worked well.

When the MMR vaccine was combined, research showed that each component was safe and effective individually. Doctors now have more than 50 years of data on the hundreds of millions of vaccine doses administered in that time. Scientists continue to monitor the vaccine’s safety to catch extremely rare side effects. 

The Infectious Diseases Society of America, a community of 13,000 clinicians, scientists and public health experts, said on its website: “There have been no deaths shown to be related to the MMR vaccine in healthy people.” There have been rare cases of deaths from vaccine side effects among immune compromised children, which is why recommendations say they should not get the vaccine, the group said.

The CDC’s page about MMR safety, dated July 2024 — which was still online as Trump made his remarks — said although vaccines can have side effects, most people don’t have serious problems from them.

“Getting MMR vaccine is much safer than getting measles, mumps, or rubella,” the CDC’s website said.

The CDC says research shows a tiny percentage of people had adverse effects from the MMR vaccine:

• Two studies showed that for every 10,000 children who get their first MMR and varicella vaccines as separate shots when they are between 12 months and 23 months, about four will have a febrile seizure during the seven to 10 days following vaccination.
• About 1 in 3,000 to 4,000 children younger than 7 years old have febrile seizures caused by a fever approximately 6 to 14 days after vaccination. While such seizures are frightening, nearly all children who have them recover quickly, and they typically don’t cause permanent damage. 

The CDC said measles can be deadly. 

Anders Peter Hviid, professor of epidemiology research in Denmark, told PolitiFact there is no evidence that the MMR vaccine is “quite lethal.”

“There is no scientific evidence to suggest that this is an unsafe vaccine,” Hviid said. Because the vaccine is made with a live attenuated virus — a weakened version of the virus — some people may have a stronger immune response, which leads to side effects such as soreness or mild fever.

“Contrast this with the possibility of getting measles,” Hviid said. “You don’t want your child to get measles.”

Dr. James Campbell, a University of Maryland pediatric infectious diseases expert, said in an email that Trump’s statement about a “5% chance” of lethality is “absolutely ludicrous.” That would result in a lot of young children dying after the MMR vaccine. That hasn’t happened.

“MMR is not lethal at all,” said Campbell, vice chair of the American Academy of Pediatrics Committee on Infectious Diseases. “We tell parents what we say for all vaccines that we recommend — they have been rigorously studied for safety and efficacy and (for MMR) given to millions of children over more than 50 years.”

Before the first measles vaccine in 1963, measles killed 400 to 500 Americans every year, most of them young children, and put 48,000 in the hospital, said Dr. Jake Scott, clinical associate professor of infectious diseases at Stanford University School of Medicine.

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MMR vaccine was combined to make it easier to vaccinate children

MMR was combined because public health officials wanted to make it easier for people to get vaccinated.

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, Orenstein previously told PolitiFact.

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.

It would take years for separate vaccines to be tested and licensed in the U.S.

In July, the number of measles cases in the U.S. surpassed all of 2025, becoming the worst year for the virus since 1991. The U.S. had 2,465 confirmed measles cases this year, as of Aug. 6. 

Roughly 92.5% of kindergartners had been vaccinated against measles in the 2024-25 school year, a drop of four percentage points from 2019-20. When more than 95% of people in a community are vaccinated, most people are protected through community immunity.

RELATED: A parent’s guide to measles: What to look for and how to prevent infection

Our ruling

Trump said when the measles, mumps and rubella vaccines are given together in the combined MMR vaccine, “there could be a possibility they’re quite lethal.”

This vaccine has been administered in the U.S. for more than 50 years. With hundreds of millions of doses given in that time, science has shown the vaccine is safe, a conclusion supported by the CDC.

When Trump was asked during his Oval Office remarks about his evidence for lethality, he provided none, saying he had heard “there are some people that say it is that way.” At a time when U.S. measles cases are rising and vaccination rates are falling, Trump is fearmongering and citing no credible evidence.

We rate this statement Pants on Fire!

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