San Diego State University has confirmed three cases and two probable cases of mumps linked to student athletes in September 2026. Although the infected students are no longer contagious, the university is hosting a screening and booster clinic for close contacts. The outbreak highlights broader trends of waning vaccine-derived immunity, which Harvard researchers cite as a driver for the resurgence of mumps in the U.S., where 157 cases have been reported in 2026.
San Diego State mumps outbreak
- ▪A prior mumps outbreak at San Diego State University in 2020 was linked to six student cases, according to the San Diego County Health and Human Services Agency.
- ▪Dr. Tanushree Ghosh, medical director for San Diego State University's student health services, announced on September 18, 2026, that the infected students were no longer contagious.
- ▪San Diego State University confirmed three cases of mumps and reported two probable cases linked to student athletes in September 2026.
Mumps transmission methods
- ▪An individual infected with mumps can transmit the virus a few days before salivary gland swelling begins and up to five days after swelling starts.
- ▪The mumps virus spreads through the air via coughing, sneezing, or talking, and through sharing saliva-contaminated items or participating in close-contact activities like playing sports.
Mumps symptoms timeline
- ▪Mumps symptoms, including jaw-swelling, puffy cheeks, fever, headache, muscle aches, fatigue, and loss of appetite, typically manifest two to four weeks after infection.
- ▪While mumps usually resolves on its own within 10 days, severe cases can lead to brain, testicle, and ovary inflammation that may cause sterility.
MMR vaccine waning immunity
- ▪Harvard University researchers state that the resurgence of mumps in the United States since 2006 is largely due to waning vaccine-derived immunity.
- ▪The measles, mumps, and rubella vaccine protects against mumps, but vaccinated individuals can still contract the virus as vaccine-derived immunity can lessen over time.
University screening clinic response
- ▪San Diego State University hosted a clinic to screen for mumps and administer booster shots to individuals who had close contact with the infected student athletes.
- ▪San Diego State University student health services collaborated with San Diego County health officials to coordinate the response to the September 2026 mumps outbreak.
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