MMR vaccine controversy reignited as split dose option considered

A top health official has suggested discontinuing the combined measles, mumps and rubella (MMR) vaccine.

In response to President Donald Trump’s recent statement warning against the use of Tylenol by pregnant women, Assistant Secretary of Health and Human Services (HHS) Jim O’Neill wrote the following in an October 6 article on X.

“I call on vaccine manufacturers to develop safe monovalent vaccines to replace the combined MMR vaccine and to split the MMR vaccine into three completely separate vaccines.”

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This request follows the CDC’s recent pullback on COVID-19 vaccine recommendations, with the agency noting that it should be an individualized decision with a health care provider, per the HHS Vaccine Advisory Committee.

An HHS spokesperson provided the statement below to Fox News Digital.

“Deputy Secretary O’Neill agrees with President Trump that it would be best to administer the measles, mumps, and rubella vaccines as three separate vaccines. Stand-alone vaccinations can potentially reduce the risk of side effects and maximize parental choice in vaccinating children.”

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HHS Secretary Robert F. Kennedy Jr. recently linked vaccines to autism as part of a broader effort to overhaul vaccination schedules and requirements in the United States.

In a statement sent to Fox News Digital, MMR vaccine maker and biopharmaceutical company Merck responded to O’Neill’s call.

“There is no monovalent vaccine licensed in the United States for measles, mumps, and single-antigen rubella.”

“There is no published scientific evidence demonstrating any benefit to separating the combined MMR vaccine into three individual injections,” the company wrote.

“Using individual components of combination vaccines increases the number of injections for the individual and may result in delayed or missed vaccinations.”

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Merck added that the development of MMR II – Merck’s version of the vaccine – was based on input from the Advisory Committee on Immunization Practices (ACIP), professional societies, scientific leaders and customers to meet the “medical and public health needs for measles, mumps and rubella vaccinations.”

According to Merck, there are “no monovalent vaccines approved in the United States for measles, mumps, and single-antigen rubella.” (iStock)

“Evidence suggests that the use of combination vaccines improves childhood immunization outcomes, increasing both completion (receipt of all recommended doses) and adherence (age-appropriate administration) rates,” they said.

“There is no monovalent vaccine licensed in the United States for measles, mumps, and single-antigen rubella.”

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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 proven to be completely safe and effective,” he said in an interview with Fox News Digital. “There would be a compliance issue if we separated.”

Measles cases increased in the United States in 2025, particularly affecting unvaccinated children. (iStock)

Siegel noted that all three viruses are “highly contagious,” although measles has been more prominent in recent outbreaks. In 2025, measles cases increased in the United States, primarily affecting unvaccinated children.

“We have seen more measles here this year than in the last 30 years due to non-compliance with the vaccine,” the doctor said. “Rubella during 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 very contagious and the vaccine is very effective.”

Fox News Digital has reached out to HHS for comment.