(CNN) The US Centers for Disease Control and Prevention voted Wednesday to recommend the use of a third "booster" shot of the measles, mumps and rubella (MMR) vaccine during outbreaks of the mumps.
Mumps is a contagious disease caused by a virus spread through saliva and mucus.
Dr. Manisha Patel, a medical officer at the CDC, said a person who received a third dose of the MMR vaccine would have increased protection against mumps compared with someone who had received only two doses.
A study at the University of Iowa "demonstrated the effectiveness of the third dose," Patel said.
Other data showed that no serious adverse events were reported among more than 14,000 people who had received a third dose during a mumps outbreak. Any of the study participants' side effects were mild, such as a stomachache.
An increasing number of outbreaks in recent years prompted the CDC to debate whether a third dose of the vaccine should be recommended, Patel explained.
Between January 2016 and June 2017, there have been 150 mumps outbreaks with 9,200 total infections, half of them in university settings.
"We're actually still hearing reports of outbreaks, and it's unclear at what time at what point these will end," Patel said. The new recommendation "provides a tool for health departments and providers to protect those persons at increased risk during an outbreak."
Before the official recommendation, a third dose has been given during outbreaks on a case-by-case basis.
For instance, Syracuse University Health Services has offered students a third dose during its ongoing mumps outbreak; as of Monday, there have been 27 confirmed and 48 probable cases of mumps on campus.
Mumps typically begins with fever, headache, muscle aches, tiredness and loss of appetite lasting a few days. Most people will then see salivary glands swell, causing puffy cheeks and a swollen jaw.
The MMR vaccine is 88% effective when two doses have been given. In people who receive just one shot, the vaccine is less effective.
Infectious disease specialist Dr. William Schaffner said the effectiveness of the vaccine "begins to wane slowly over 10 or 15 years."
However, people who have been vaccinated "still have partial protection," said Schaffner, who is also a professor at Vanderbilt University Medical School. If you do get the mumps, you will get a milder case than if you had never been vaccinated, he explained.
Most recent outbreaks have occurred among vaccinated people, according to Patel.
Just before the CDC made its recommendation Wednesday, an advisory committee reviewed data from recent outbreaks, including the number of vaccinated people who became infected. In its deliberations, the panel assessed the impact of a third dose in decreasing the size and duration of outbreaks.
The CDC currently recommends that children get their first dose when they are 12 to 15 months old and a second dose at 4 to 6 years.
Outbreaks of mumps tend to occur in areas where there is crowding and close contact, according to Patel. Campuses are a typical site for outbreaks because of the sharing of saliva: by coughing, sneezing, kissing and sharing utensils, lipstick or cigarettes.
The incubation period for mumps ranges from 12 days to 25; symptoms last at least two and usually more than 10 days. Mumps can occasionally cause complications, especially in adults. These include deafness and inflammation of the brain, ovaries, breast tissue or testicles.
Since it is caused by a virus, mumps will not respond to antibiotics. Doctors generally recommend bed rest and over-the-counter pain relievers. Most people with mumps recover completely in a few weeks, according to the CDC.
Before the US mumps vaccination program started in 1967, the CDC received reports of 186,000 cases each year. The actual number of cases was probably much higher but not always reported since most doctors considered the mumps a typical childhood disease. Since the development of the vaccine, cases have decreased by more than 99% in the United States.
Each year, the number of mumps cases fluctuates within a range of a couple hundred to a couple thousand, according to Patel.
In 2016, the United States experienced the highest number of mumps cases in a decade: more than 6,000, according to CDC preliminary reports.
The number of cases is high this year, too. As of October 7, the CDC has received reports of 4,667 total mumps infections in 47 states and the District of Columbia for the year.
The third booster shot should be helpful to students at Syracuse University and other places where infections are being passed from person to person.
"It's one way to help curtail an outbreak," Schaffner said. "Although it's not a magic potion."