Whatcom Co. has first mumps case since 2018. Could it make a comeback?

After a seven-year lull, Whatcom County has recorded a case of the mumps. On Monday, May 12, Whatcom County Health and Community Services announced that it had confirmed a case of the disease for the first time since 2018.

The U.S. is currently seeing a spike in measles cases, which experts largely attribute to falling vaccination rates, but mumps is covered by the same shot — the measles, mumps and rubella (MMR) vaccine.

Through April 24, there had been no confirmed mumps cases in Washington in 2025, according to the Centers for Disease Control and Prevention, although there were reports of two suspected cases in state prisons earlier this year.

So far, county officials say that there isn’t much risk of additional spread.

“Though vaccine-preventable diseases should be of concern to the public, the risk from this particular confirmed case we’ve said is low,” Whatcom County Health Officer Dr. Amy Harley told The Herald in a phone interview. “That’s because this individual is recovering at home, and anybody who’s been exposed to that person has been contacted.”

Is Whatcom County at risk of a mumps outbreak?

While mumps is a contagious disease, it doesn’t spread as easily as measles, meaning there’s less risk of a widespread outbreak.

“Unlike measles virus, which is transmitted through the air, mumps is transmitted by direct contact with saliva or respiratory droplets or objects like water bottles that could be contaminated by saliva or respiratory secretions,” Harley said. “So it is a moderately infectious virus, but not as quite as contagious as measles.”

That said, there are a few factors that suggest Whatcom County is at risk of seeing an uptick in mumps cases.

“Prior to the pandemic, it did look like cases of mumps were increasing in the U.S. But as with other viruses that are transmitted by the respiratory route, cases of mumps in the U.S. decreased during the COVID-19 pandemic,” Harley said. “So it’s possible we may see an increase again.”

According to Washington State Department of Health data, the state has seen between one and 11 cases of the disease each year since 2020, after seeing 55 cases in 2019, 58 in 2018, 779 in 2017 and 152 in 2016. Prior to that four-year stretch, case counts had been in the single digits for seven years in a row.

Whatcom County vaccination rates

Another factor is the local vaccination rate.

Two doses of the MMR vaccine is 86% effective against mumps transmission, according to the CDC. Prior to the vaccine becoming widely available in 1967, the U.S. saw around 186,000 mumps cases a year, according to the CDC. In the early 2000s, nationwide case counts typically sat around 200 or 300, although a series of outbreaks in the late 2000s and 2010s pushed that number into the thousands, before case counts fell sharply during the COVID-19 pandemic.

Harley said that school immunization rates are one of the most telling and reliable indicators of vaccine rates. The proportion of Whatcom County kindergarten students who were up to date on their mumps vaccine stood at 86.8% in the 2023 to 2024 school year.

That doesn’t represent a sharp decline from past vaccination rates, although it is on the lower end of what Whatcom County has seen in the past. The Washington State Department of Health published the county’s mumps vaccination rate from 2004 to 2012. In that time, the vaccination rate ranged from 86.3% to 93.6%.

“Eighty-six percent of Whatcom County kindergarteners are up to date on MMR vaccine … it has been sort of a general downtrend,” Harley said.

According to DOH, that’s just below the threshold needed to prevent community spread.

“When vaccination rates are high, it’s much harder for the disease to gain a foothold,” Washington State Department of Health spokesperson Raechel Sims told The Herald in an email. “The herd immunity threshold for mumps is estimated at 88% to 92%.”

The state as a whole has seen a similar trend, according to Sims.

“MMR vaccination coverage for children in Washington dropped during the pandemic and has not yet recovered,” Sims said. “The sharpest decline occurred between 2019 and 2021, and rates remain low. As of 2024, only about 75% of children aged 19 to 35 months are up to date on their MMR vaccinations, according to the Washington Immunization Information System.”

The risk of an outbreak can be higher than those numbers suggest, according to Harley, since people who are unvaccinated tend to come in clusters.

“Those vaccination rates for MMR are not enough to maintain herd immunity, meaning that we are at risk for outbreaks, especially because often there are social connections between groups who all tend to be under-immunized,” Harley said.

Mumps symptoms

According to the CDC, the disease tends to cause puffy cheeks and a swollen jaw. It can also cause fever, muscle aches, headaches and loss of appetite. Symptoms often take two to four weeks to appear. Possible complications include hearing loss and inflammation of the brain, pancreas, testicles, ovaries or spinal cord tissue. Death from the mumps is possible, although estimates place its fatality rate below 0.1%.

According to Harley, it can be easy to forget how severe mumps can be because of how widespread the vaccine is.

“As vaccine-preventable diseases like mumps have become more rare, it’s easy to forget how devastating they once were,” Harley said. “They seem like just stories in textbooks, but they do cause real suffering and disability and even death.”

This story was originally published May 14, 2025 at 2:45 PM.