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Mumps is one of those childhood diseases we’ve almost been able to forget about.
Before the vaccine against it was developed in the late 1960s, mumps was a rite of passage. The virus mostly struck children ages 5 to 9 with a week or so of high fevers, headaches, exhaustion and chipmunk cheeks from swollen glands. It also led to deafness and swollen testicles that could cause male infertility.
For decades, since the advent of the vaccine, there had been only a few hundred cases a year in the U.S.
But, the disease is making a comeback: In 2016, there were 6,000 cases of mumps, and nearly as many last year.
So, researchers at Harvard’s Chan School of Public Health set out to figure out what's going on.
In a new study out Wednesday in Science Translational Medicine, the researchers attribute the jump in cases to a flaw of the vaccine: Over time, the protection it provides to the immune system wanes, says Yonatan Grad, an assistant professor at the Chan School and a co-author of the study.
The pattern of cases suggests the vaccine itself is the cause, he says, rather than a lack of vaccination, or a change in the virus.
The recent jump in cases has come mainly from college students and other young adults — many of whom were up-to-date on their shots, says Joseph Lewnard, a research associate at the Chan School, and another co-author of the study.
“On average, about 50 percent of people would be expected to lose protection after 19 years, and 25 percent after as few as eight years,” Lewnard says.
Grad says it’s taken decades to figure out that the vaccine’s protection wanes with age because so many Americans were already immune to mumps from having caught it as children.
“We've been replacing the population of people who did experience clinical mumps as children over time with more and more birth cohorts of children who have only been exposed through the vaccine,” he says. “So there's been a buildup of people whose protection is only from this possibly shorter-lived vaccine-derived immunity rather than from natural infection.”
He says he found it reassuring that their research did not support the idea that the virus is mutating so that the vaccine no longer protects against it even when fresh.
“The epidemiologic pattern doesn't really look like what we'd expect it to look like if there were truly a vaccine-escaping virus out there circulating and causing these outbreaks,” he says.
Grad says it’s still too early to decide, but worth investigating whether college students should be routinely given mumps booster shots before heading off to school.
Following a recommendation from a federal panel in January, Lewnard adds that anyone exposed to an outbreak should consider getting a booster shot to shore up their protection.
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