President Trump’s executive order to separate the measles, mumps, and rubella vaccines into individual shots could potentially cause significant harm. If policymakers succeed in influencing vaccine manufacturers, it might result in more missed vaccinations and an increase in childhood illnesses. Before exploring this issue further, it is essential to understand the origins of the combined vaccine.
In March 1963, a 5-year-old girl named Jeryl Lynn experienced a sore throat in the early hours of the morning. Her father, a 6-foot-1 widower who had suffered the loss of his wife to breast cancer just four months prior, noticed the lumps on her neck. As a scientist at the pharmaceutical company Merck, he consulted “The Merck Manual,” a medical guide, and exclaimed, “Oh my God, you’ve got the mumps.”
After putting his daughter back to bed and informing the housekeeper of his departure, he went to his office and gathered cotton swabs and a vial of nutrient broth. He returned home, swabbed Jeri’s throat, and reassured her before heading back to work. He used the virus sample to infect chicken eggs and later transferred it to culture dishes containing chick cells. As the virus adapted to chickens, it became less effective at infecting humans, transforming into a vaccine.
That father was Maurice Hilleman, the scientist who developed vaccines for meningococcus, pneumococcus, and the licensed mumps vaccine in 1967, which remains in use in the U.S. He later combined the mumps vaccine with those for measles and rubella to create the MMR vaccine, licensed in 1971. Each administration of the Merck MMR vaccine stands as a testament to a father’s enduring battle against a virus that once afflicted his daughter.
Hilleman, known for his tenacity, was raised on a Montana farm by his aunt and uncle after his mother died during childbirth. He was as fond of firing people as President Trump is reputed to be, keeping a collection of shrunken apple heads carved by his daughter Kirsten to represent employees he had dismissed. These insights are drawn from vaccine developer Paul Offit’s biography of Hilleman, compiled from extensive interviews.
Prior to the introduction of the vaccine, mumps was the leading cause of deafness among children, although it is considered less severe compared to the other diseases protected against by the MMR vaccine. Before widespread use of the measles vaccine, there were 48,000 hospitalizations annually in the U.S., along with 1,000 cases of encephalitis and approximately 500 deaths. Rubella, while typically mild, led to birth defects. An epidemic from 1964 to 1965 resulted in 20,000 infants being born with congenital rubella syndrome. Among these, 11,000 were born deaf, 3,500 blind, and 1,800 with intellectual disabilities.
Children’s author Roald Dahl shared his personal tragedy of losing his 7-year-old daughter to measles encephalitis in 1962, saying, “In an hour, she was unconscious. In twelve hours she was dead.”
There is also evidence that measles infection can weaken the immune system, making children more susceptible to other infectious diseases in the future.
In discussing medical interventions, researchers weigh benefits against risks. Over six decades of use have demonstrated the MMR vaccine’s substantial benefits. The most significant controversy regarding its safety relates to claims of a connection to autism. However, numerous studies confirm that the MMR vaccine does not increase the risk of autism spectrum disorders. Additionally, thimerosal, a preservative not found in the MMR vaccine, has not been linked to harm despite allegations. There is no evidence that multiple vaccines administered together increase autism risk.
Japan provides a cautionary tale. In 1989, Japan introduced an MMR vaccine using a different mumps virus strain, which was suspended in 1993 due to a rise in meningitis cases not caused by bacteria. Consequently, only separate vaccines for measles, mumps, and rubella were available.
Mumps remains endemic in Japan, with over 300 cases of mumps-induced hearing loss reported in 2015 and 2016, according to one survey. Measles vaccination rates fell to 83% in 2001, leading to an outbreak affecting an estimated 265,000 children. Japan also experienced a rubella epidemic in 2012. While these instances cannot be directly attributed to the MMR withdrawal—other factors are involved—they highlight the dangers of low vaccination rates. Notably, the withdrawal did not impact autism rates.
Japan introduced a combined measles-rubella vaccine in 2006, and an expert panel recently approved an MMR vaccine, though it is not yet available. The country was recognized for eliminating measles in 2015 and rubella in 2025.
In the U.S., single-dose measles, mumps, or rubella vaccines are not marketed. Whether they will become available remains uncertain. Reduced vaccine uptake could exacerbate the current measles outbreak. A Stanford modeling study predicts that measles could become endemic at current vaccination rates, with a 10% decline in MMR vaccination potentially resulting in 11 million cases over 25 years.
Such prospects might lead one to imagine Donald Trump being visited by the ghost of Maurice Hilleman, in a Dickensian fashion.
