People in the U.S. are already supposed to get two doses of a vaccine that aims to thwart the spread of mumps, but a third round might be needed, too.
Researchers behind a study published in the journal Science Translational Medicine made that recommendation. They examined six studies from 1967 to 2008 that looked at the effectiveness of the MMR vaccine, which covers measles, mumps and rubella.
Joseph Lewnard and Yonatan Grad — an epidemiologist and immunologist at Harvard University, respectively — got the idea for their study after an outbreak of mumps at their university, according to ScienceMag.org.
The Centers for Disease Control and Prevention reports that the number of mumps infections has decreased by 99 percent since the introduction of a vaccine for the virus in 1967. But 2016 and 2017 witnessed a spike in mumps infections, according to the CDC, with many infections occurring in places such as colleges where people are in close quarters.
People are supposed to get one dose of the MMR vaccine when they are 12 to 15 months old, the CDC recommends, and then receive a second shot between ages 4 and 6.
After examining data from the six studies, Lewnard and Grad estimated that the average person’s immunity to mumps lasts about 27 years after their last vaccine but it varies by each person. They also found that their predictions of outbreaks lined up with what happened in the real world, the study says.
There was an outbreak of mumps among 10- to 19-year-olds around the late 1980s. That group only received one shot of the MMR vaccine at the time, the study says, and the scientists used a predictive model that found an outbreak of mumps among that group was more likely at the time.
Then there was a spike in mumps outbreaks among college students starting in 2006 after the CDC recommended a second shot in 1989, the study found. Lewnard and Grad’s model also predicted that would happen after the second dose.
Those findings led the researchers to recommend a third dose of MMR to keep college students and other young adults immune to the virus and reduce any further outbreaks of it.
Lewnard told CNN that he and his colleague recommend a third shot at 18 because “that’s the age people are beginning to congregate.”
There aren’t any increased outbreaks among younger people, the study also found, suggesting that the vaccine isn’t any less effective — but rather that people’s immunization declines over time.
William Schaffner, an infectious disease specialist not involved in the study, said it’s still unclear how effective a third shot could be.
“That’s a large unknown,” he told CNN, “and that’s why, at the moment, the (immunization committee) has not recommended a third dose for everybody in adolescence.”
And Stanley Plotkin, a vaccine expert at VaxConsult, said in an interview with ScienceMag.org that the mumps virus could have also mutated in a way that gives it more of a resistance to the vaccine. He pointed to some studies that suggest the vaccine could be less effective now.
Still, he supports the third shot.
“The simplest thing, the thing we can do today, is to propose a third dose of MMR on entry to university colleges,” he told ScienceMag.org, “which would help to prevent outbreaks from occurring.”
Eighty-two percent of Americans said that children should receive the MMR vaccine, according to a 2017 poll from the Pew Research Center, which also found that 66 percent of people said the risk of complications from the vaccine is “low.”
But a 2015 Gallup poll found that fewer people in the U.S. think its “extremely important” to get their children vaccinated. Just 54 percent said that in 2015, according to Gallup, compared with 64 percent of people who said the same in 2001.