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The Salt Lake County Health Department announced two confirmed cases of mumps and is investigating four additional cases.

SALT LAKE CITY — Health officials on Thursday confirmed two cases of mumps among Salt Lake County residents. Another four cases are being investigated.

All six cases involve individuals either attending the same school or their family members, and both confirmed cases had been vaccinated against mumps.

"Vaccines are not 100 percent effective for 100 percent of people who are vaccinated," said Gary Edwards, executive director at the Salt Lake County Health Department. He said immunizations like the measles, mumps and rubella vaccine do more than prevent disease, but also decrease the severity of illness if it is contracted and also possibly limit the spread of disease.

"Two doses of MMR are necessary to be fully protected," Edwards said.

The U.S. Centers for Disease Control and Prevention recommends two doses of the vaccine, as one (typically given between 12 and 15 months of age) is reportedly 78 percent effective in preventing mumps and the second, recommended between ages 4 and 6, increases the effectiveness to about 88 percent.

Edwards said that while the number of people vaccinated in Salt Lake County has remained much the same over the years, declining rates throughout the state and country have compromised more people who aren't up to date on their vaccinations.

Children and those with already compromised immune systems are at greatest risk.

In 2016, 5,311 mumps cases were reported to the CDC, whereas in just January this year, 27 states have reported 495 cases.

The local mumps cases join at least two confirmed measles cases in Salt Lake County, as another case of measles was confirmed during the week.

The MMR vaccine is more effective at preventing measles, reaching 97 percent effectiveness with two doses, Edwards said.

Symptoms of each disease varies, but both include a fever. Mumps also presents with headache and muscle aches, fatigue and swollen salivary glands under one or both ears. Some people who get mumps have very mild or no symptoms, and many recover within a few weeks, but some cases can result in serious complications, including deafness, meningitis or encephalitis.

Measles symptoms include cough and runny nose, as well as a rash that spreads all over the body.

Both diseases are highly contagious, which is why the health department is acting with such urgency.

"For the broader public who has not been exposed, this is a reminder to check your vaccinations and make sure you're protected," Edwards said.

Both individuals with confirmed mumps in Salt Lake County have been quarantined during their most contagious time, and anyone they have been in contact with has been informed of increased risk, said Tiar Kiphibane, manager of the department's bureau of infectious disease.

She said a report of the four suspect cases will be available next week.