An outbreak of mumps has sidelined 17 football players at San Diego State University since September 18. SDSU requires proof of two doses of the measles, mumps, and rubella vaccine for entry.

As of September 10, 2026, 31 jurisdictions reported 157 mumps cases.

Why Are These Outbreaks Happening?

Current outbreaks of mumps are largely thought to be due to waning immunity. Two doses of the MMR vaccine are 97% effective against measles and 86% effective against mumps. So a number of people never developed immunity from vaccination—they were, luckily, never exposed before.

In 2016-19, there were large outbreaks of mumps—with a high of 6369 cases in 2016 . Most of the mumps patients said they had received both doses of the MMR vaccine. But we now know that antibody protection declines by 12% per year for mumps, and protection only lasts about 10 years .

How And Where Is Mumps Spread?

Mumps is a viral infection and, like mononucleosis, is transmitted through secretions and respiratory droplets. It’s most common where people are in close quarters—like school dormitories, prisons , and now ICE detention centers.

Although I treated patients for more than 40 years, I never saw a patient with mumps, a testament to our successful immunization programs.

While mumps commonly presents with fever, achiness, and then swollen parotid glands, it can also be asymptomatic or subclinical —in up to 20% of cases, per ECDC , the European CDC— fueling it’s spread.

Each person can infect 4-7 others . The incubation period is 12-25 days. One problem is that a patient is infectious and shedding virus for 1-2 days before developing any symptoms and for 5 days after.

Orchitis, or testicular swelling, can occur in up to 40% of men , and the painful swelling can last for weeks. Testicular atrophy can occur in almost half of those affected. Impaired fertility occurs in 7-13% , but total sterility is uncommon.

Alberta, Canada had a great, suggestive PSA, with two burning balls going down in a blaze of glory, and stating, “The swelling’s not so bad. It’s the severe testicular pain…Protect yourself against the mumps. Get Immunized.”

Their PSA cautioned that mumps could cause sterility, meningitis, and deafness.

In one year, 2018-2019, the CDC reported outbreaks in 57 immigration detention facilities in 19 states . Mumps sickened 898 adult migrants and 33 detention center staffers. Most (84%) were exposed while in custody. At least 13 patients had to be hospitalized. Detainees are quarantined for 25 days. Fewer cases have been reported since 2020. Why that happened is not clear to me.

The Trump administration has been focused on reducing the number of childhood vaccinations. In an August Executive Order, President Trump advised separating the MMR into individual components. He wants to enhance parental “rights” to opt their child out of immunizations. This ignores that we need a certain level of herd immunity to protect everyone, and also that a child with measles can infect and kill others who are immunocompromised or who are too young to have been vaccinated.

Trump’s proposal has been widely criticized as being impractical and eroding public trust. Spreading vaccinations across multiple visits will be more costly and lead to lower immunization rates. We already have more than 1,000 measles cases and 5 deaths in Pennsylvania--more than in 35 years.

At least 23 states have said they will continue with the recommendations of the American Academy of Pediatrics rather than those recommended by Robert F. Kennedy Jr and the Department of Health and Human Services.

Kennedy has vociferously opposed the MMR vaccine and falsely claimed that it causes autism and supports a delayed and stretched-out immunization schedule . He has produced so many falsehoods that the experts-led Defend Public Health group has devoted a weekly column to his “Whopper of the Week.”

Kennedy has also repeatedly claimed that teenage boys have only half the sperm counts of men in their 60s. He added, “We have fertility rates that are just spiraling .”

The irony is that the MMR vaccine that Kennedy opposes is protective against damage to the testicles and infertility.

With the growing measles epidemic in the U.S., there is one other caution to mention. Measles causes an immune amnesia . The body forgets how it responded to previous infections. As of October 1, 2026, the CDC reports 3,887 confirmed* measles cases in the U.S., and the rates of new cases has been rapidly increasing since 2023.

Each of these people will be immunocompromised for up to five years and are likely to have repeated infections. They lose 11% to 73% of the antibodies they had previously. All of these illnesses, deaths, and heartache could be avoided by just staying with our current vaccine schedule. In fact, one might argue that revaccination be considered for those who survived measles.

Before 1900, almost one in five children died in the U.S. before their fifth birthday from diseases that are now preventable with immunizations. Why would we want to go back to the pre-vaccine era? Vaccines save countless lives—please use them!