An outbreak of mumps among New Jersey college students has highlighted the "weak sister" in the MMR vaccine.
At least eight students at the Stevens Institute of Technology in Hoboken have contracted the contagious virus despite having received two doses of the measles, mumps and rubella vaccine, according to the college.
"All Stevens' students are required to have full vaccinations before attending the University," the college said in a statement, adding that "outbreaks of mumps have occurred in vaccinated populations before."
More than 95 percent of the people who receive a single dose of MMR develop some immunity to all three viruses, according to the U.S. Centers for Disease Control and Prevention. But the mumps portion of the shot is only 88 percent effective in preventing the disease.
"Of the three vaccines that are given together, mumps is what we might call 'the weak sister,'" said Dr. William Schaffner, and infectious disease expert and chair of preventive medicine at Vanderbilt University Medical Center in Nashville, Tenn. "We really do expect vaccines to be perfect and, of course, they aren't perfect. Medical science provides us with vaccines that have different degrees of effectiveness, approaching but never reaching perfection."
"When you are vaccinated [against mumps], the illness you get is much milder," Schaffner added.
The MMR vaccine is 99 percent effective against the measles and 90 percent effective against rubella, according to the CDC.
Stevens' students suspected of having mumps were "isolated" and then sent home, according to the college.
"There have been no reports of newly symptomatic cases since the initial cases last week," the college said.
Symptoms of mumps such as fever, aches and swollen glands can take more than two weeks to appear. And while most mumps sufferers recover after a week or two, the disease can cause serious complications like inflammation of the testicles, ovaries and brain as well as deafness, according to the CDC.