The number of mumps cases in Washington state has eclipsed the 100 mark as health officials put the tally at 107 as of Tuesday. King County accounts for 86 percent of cases (93) and the number reported in Pierce County has grown to nine.


In King County, where two-thirds of the cases have been reported in children 17 and younger, 68 percent are reported up to date on their measles-mumps-rubella vaccination (MMR).

Washington state is not the only place reporting high numbers of mumps cases in fully vaccinated individuals. In Arkansas, the state with by far the most mumps cases reported this year at about 2300 to date,  90% to 95% of school-aged children and 30% to 40% of adults involved in the outbreak have been fully immunized.

So the question is–Does the mumps vaccine work?

In a recent post by Jeff Duchin, Health Officer, Public Health – Seattle & King County, he writes:

When many people have been vaccinated in a setting where a mumps cases are occurring, most of the vaccinated people are protected, but mumps cases can still occur in a small percentage. This may make it seem like the vaccine isn’t working. However, the occurrence of mumps during outbreaks in highly vaccinated populations does not mean the vaccine isn’t working.

  • Data from many of these outbreaks indicate that mumps vaccination provides significant protection. In several studies, vaccine effectiveness was estimated at approximately 80% and higher, which shows a great benefit to vaccination.
  • In addition, the rates of mumps among vaccinated persons in these outbreaks were low, ranging from 2% to 8%, compared with mumps infection rates of 25% to 49% in unvaccinated persons.
  • In other words, although a minority of vaccinated people may get mumps during an outbreak, the risk is greatly reduced compared to unvaccinated persons. This means many more people would become ill in the absence of vaccination.
  • In addition, fewer and less severe complications are reported in people that have been vaccinated.

He goes on to say:

Mumps vaccine provides meaningful protection, but is not perfect. There are a few possible reasons why some vaccinated people can still get mumps:

  • Primary vaccine failure has been suggested to have a role in mumps outbreaks, but this has not been proven and based on studies, it would be uncommon.
  • Protection may decrease with time since vaccination. This has been suggested in some studies but not others.
  • There may be differences between the vaccine strain and mumps viruses circulating in the community. Some studies suggest this may be playing a role, but no studies have shown this to be true.
  • Failure to store and administer the vaccine correctly (this would be uncommon) could impact the effectiveness of the vaccine.
  • A combination of these factors.
  • Typically, a person is immune from getting mumps again after having had the disease. However, it is important to note that even mumps infection does not provide 100% protection – rarely, mumps can occur even after a natural mumps virus infection.

LISTEN: Arkansas, mumps and the MMR vaccine: A discussion with Dr Dirk Haselow