Mumps at SDSU: Should You Get a Third MMR Shot?
If you're a close contact of a mumps case at SDSU, or on any campus where public health has declared an outbreak and is offering boosters, take the third MMR shot. It's free, well tolerated, and cuts your short-term risk by about three quarters. Your two childhood doses are still doing their main job, which is keeping breakthrough cases mild. What they're no longer reliably doing is blocking infection. Mumps antibodies fade faster than the measles and rubella parts of the vaccine, and most undergraduates got their second dose around kindergarten.
By September 30, San Diego State had 14 confirmed and 1 probable mumps case, concentrated in the football team, with earliest symptoms on September 6. Everyone confirmed to have mumps had already received two MMR doses. That's not a surprise. About four in five large US mumps outbreaks from 2010 to 2015 involved college campuses, and most of those cases had already been vaccinated twice. San Diego County is running a free booster clinic at the Calpulli Center for students identified as close contacts of a case, which is the one intervention that moves the odds during an active cluster.
A football team is where the virus thrives
The virus moves through close-range droplet contact, so a locker room and shared housing give it everything it needs. A person is contagious from two days before parotid swelling through five days after, and up to a fifth of mumps infections stay asymptomatic while still shedding virus. The pattern on campuses is consistent. A 2016 outbreak at the University of Iowa reached 301 students; 86% had two doses and 12% had already received three. Clusters at four Indiana universities and on a New York City campus looked the same, with most cases already vaccinated.
Your kindergarten shots have been fading
The mumps part of MMR raises neutralizing antibodies, and those antibodies drop roughly 7% to 10% per year after dose two. At Iowa, protection in students whose second dose was more than thirteen years earlier fell to about 32%, with an uncertainty range that reached no benefit at all. That's the exact profile of today's undergraduates: dose two at age 4 to 6, now 18 to 22. Attack rates in Iowa tracked the same curve, climbing from under 2 per 1,000 in recently vaccinated students to roughly 18 per 1,000 in those vaccinated 16 to 23 years earlier.
The complication side is better news. Two doses still blunt the parts of mumps you most want to avoid. Vaccinated men who catch mumps get orchitis in about 4% to 12% of cases, versus 15% to 30% or more without vaccination. Symptomatic aseptic meningitis stays under 2% and is usually self-limited. Pancreatitis and sensorineural hearing loss remain well below 1%. When vaccinated people do catch mumps, they shed less virus, land in the hospital less often, and recover faster.
How much a third dose helps
During the Iowa outbreak, attack rates ran 6.7 per 1,000 in three-dose recipients versus 14.5 per 1,000 in two-dose. After adjusting for time since dose two, the third dose cut mumps risk by about 78% in the following weeks. A village outbreak in New York showed a similar three-quarters drop. The antibody boost is real but temporary. Titers rise at one month and drift back toward baseline over one to three years. That's why ACIP has recommended the extra dose since 2017 only for people public health identifies as at increased risk during an active outbreak.
Side effects track with the vaccine's usual profile: a sore arm in about a quarter of recipients, a headache in roughly one in eight, mild joint aches in about one in ten, usually gone in a day or two. No serious adverse events were reported in that study of young adults, and pregnancy and severe immune suppression are contraindications.
When it's worth taking
If you're an SDSU football player, a close contact of a confirmed case, or at any campus where public health has declared an outbreak and is actively offering boosters to an identified at-risk group, the shot is a reasonable call. It's free, safe, and meaningfully lowers your short-term odds in the window that matters. If you're a vaccinated adult outside such a group, the data don't support a routine third dose. Your childhood shots still protect against the serious complications, and the antibody bump from a booster fades within a few years.
Symptoms to recognize: parotid swelling on one or both sides, fever, headache, earache, testicular pain. Incubation runs 12 to 25 days, so symptoms can show up weeks after an exposure. If swelling starts, five days of isolation from that point is the standard; the contagious window runs from two days before swelling through five days after. About half of mumps infections present with only nonspecific symptoms, which is one reason outbreaks keep spreading before anyone notices.