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A top health official has suggested breaking up the combination measles, mumps and rubella (MMR) vaccine.
In response to President Donald Trump’s recent statement warning about pregnant women’s use of Tylenol, Health and Human Services (HHS) Deputy Secretary Jim O’Neill wrote the following in an Oct. 6 post on X.
“I call on vaccine manufacturers to develop safe monovalent vaccines to replace the combined MMR and break up the MMR shot into three totally separate shots.”
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This request follows the CDC’s recent pullback on COVID-19 vaccine recommendations, as the agency noted that it should be an individualized decision with a healthcare provider in accordance with the HHS vaccine advisory panel.
A spokesperson for HHS provided the below statement to Fox News Digital.
“Deputy Secretary O’Neill agrees with President Trump that immunizations for measles, mumps and rubella would be best administered as three separate vaccines. Standalone vaccinations can potentially reduce the risk of side effects and can maximize parental choice in childhood immunizations.”
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HHS Secretary Robert F. Kennedy Jr. has recently linked vaccines to autism in a wider effort to review vaccine schedules and requirements in the U.S.
In a statement sent to Fox News Digital, MMR vaccine maker and biopharmaceutical company Merck responded to O’Neill’s call.
“There are no approved U.S. monovalent measles, mumps and rubella single antigen vaccines.”
“There is no published scientific evidence that shows any benefit in separating the combination MMR vaccine into three individual shots,” the company wrote.
“Use of the individual components of combination vaccines increases the number of injections for the individual and may result in delayed or missed immunizations.”
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Merck added that the development of MMR II – Merck’s version of the vaccine – was based on the input of the Advisory Committee on Immunization Practices (ACIP), professional societies, scientific leaders and customers to meet the “public health and medical need for vaccination against measles, mumps and rubella.”
“Evidence suggests that use of combination vaccines improves childhood vaccination outcomes, increasing both completion (receipt of all recommended doses) and compliance (age-appropriate administration) rates,” they said.
“There are no approved U.S. monovalent measles, mumps and rubella single antigen vaccines.”
Fox News senior medical analyst Dr. Marc Siegel agreed that the MMR vaccine should not be separated.
“The MMR vaccine should not be separated because it has been tested this way for decades and found to be completely safe and efficacious,” he said in an interview with Fox News Digital. “There would be a problem with compliance if we separate.”

Siegel noted that all three of the viruses are “highly contagious,” although measles has been more prominent in recent outbreaks. In 2025, measles cases surged across the U.S., mostly infecting unvaccinated children.
“We have seen more measles here this year than in the past 30 years because of non-compliance with the vaccine,” the doctor said. “Rubella in pregnancy causes hearing loss and birth defects and mumps threatens fertility.”
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Siegel added, “We need to encourage compliance because these viruses are highly contagious, and the vaccine is highly effective.”
Fox News Digital reached out to HHS for comment.
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