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One injection, three diseases. The MMR vaccine protects against measles, mumps and rubella, and the idea of packing several vaccines into one shot owes a great deal to a farm boy from Montana. Maurice Hilleman is not a household name, yet his team made many of the vaccines children receive. This post covers how he made the mumps vaccine, what the trial numbers showed, and why measles needs such high vaccine coverage.
Who was Maurice Hilleman?
A chapter on his life by Theodore Tulchinsky in Case Studies in Public Health (2018) tells the story. Hilleman was born in 1919 in Miles City, Montana. His mother died two days after his birth, and he was raised partly by an uncle on the family farm. He won a scholarship to Montana State University, then earned a PhD in microbiology at the University of Chicago in 1944.
He chose industry over academia. After work at E.R. Squibb and at the Walter Reed Army Medical Center, he joined Merck in 1957 to lead its virus and vaccine research. Tulchinsky writes that from the 1950s to the 1990s, Hilleman and his team created more than 40 experimental and licensed vaccines. He received the US National Medal of Science in 1988 and died in 2005.
How did his daughter help make the mumps vaccine?
In 1963 his five-year-old daughter, Jeryl Lynn, fell ill with mumps. Hilleman took a throat swab, grew the virus in the lab, and began weakening it. Tulchinsky records that the resulting vaccine was licensed in 1967 and named the Jeryl Lynn strain after her.
Hilleman's own 1966 paper with Eugene Buynak describes the method: the virus was attenuated "by passage in embryonated hens' eggs and in cell cultures of chick embryo". Growing a human virus repeatedly in bird cells selects strains that are good at living in those cells and worse at causing disease in people.
The large field trial followed. In the New England Journal of Medicine in 1968, Hilleman's team reported giving the vaccine to 6,283 children who had no prior immunity. The seroconversion rate, the share who made antibodies, was 96.9% in children, and protection against natural mumps was "of the order of 95 per cent".
How did MMR come together?
By then there were separate vaccines for measles and rubella. Tulchinsky notes that in 1968 Hilleman's team produced a more weakened measles vaccine, and the combined measles, mumps and rubella vaccine was licensed in the United States in 1971.
The key question was whether three live viruses given together would interfere with each other. A 1971 trial reported in JAMA gave the combined vaccine to 715 children aged 7 months to 7 years who had no antibodies to any of the three viruses.
Worked example: reading the MMR trial
The JAMA abstract reports that 96% developed measles antibodies, 95% mumps antibodies and 94% rubella antibodies.
Measles: 0.96 × 715 = 686.4, so about 686 children.
Mumps: 0.95 × 715 = 679.25, so about 679 children.
Rubella: 0.94 × 715 = 672.1, so about 672 children.
The authors concluded the combination worked "without impairment of antibody response and without significant increase in clinical reaction". Three injections had become one.
Why does measles need such high coverage?
The WHO measles fact sheet says one person with measles can infect up to 18 others. A simple model used in epidemiology says that if each case would infect R others in a group with no immunity, the outbreak stops growing once more than 1 − 1/R of people are immune.
With R = 18: 1 − 1/18 = 1 − 0.056 = 0.944, so about 94% of people need to be immune.
That is why WHO recommends two doses: not every child responds to the first. WHO also reports that measles deaths fell from an estimated 780,000 in 2000 to 95,000 in 2024. The fall is (780,000 − 95,000) / 780,000 = 0.878, or about 88%.
Which mistakes does this help you avoid?
Mixing up live and inactivated vaccines. MMR uses live, weakened viruses. The NCERT Class 12 chapter Human Health and Disease describes vaccines as "inactivated/weakened pathogen" or antigenic proteins.
Thinking vaccines give instant immunity. A vaccine works by building memory B and T cells, which takes time after the dose.
For where vaccination began, read our post on Edward Jenner and vaccination.
What can a student take from Hilleman's way of working?
Use what is in front of you. A sick child at home became the source of a vaccine strain.
Test at scale. A trial in more than 6,000 children, not a handful, showed how well the vaccine protected.
Ask the practical question. Combining vaccines only helps if the parts do not interfere, so he tested exactly that.
Percentages, denominators and thresholds like 1 − 1/R come up often in biology questions. The Fermi Problem Library has worked problems with a step-by-step solver that explains the reasoning rather than printing an answer.
Try it now: if a disease has R = 5, what share of people must be immune to stop it spreading?
