The number of mumps cases at Harvard University has risen to nine, sparking concerns among health officials that the viral illness will spread when students leave for spring break next week.
The nine cases are among 12 laboratory-confirmed mumps cases in Massachusetts since Jan. 1, according to the state Department of Public Health.
The University of Massachusetts Boston and Bentley University in Waltham each acknowledge having a mumps case. The health department declined to provide information about the 12th person.
Health officials are investigating more than two dozen other cases at Harvard that might be mumps, but the cause of those illnesses has not been confirmed.
Mumps outbreaks occurred on college campuses in 2006, 2008, and 2013, said Dr. Alfred DeMaria, director of communicable diseases for the Massachusetts Department of Public Health.
“Once a college campus starts circulating mumps, it becomes a problem,” he said. “I wish we understood better why.”
Inadequate vaccination does not seem to be the source of the problem this year, DeMaria said. Most of the students were fully immunized, as required by state law. Instead, the outbreak may be the result of the vaccine failing to work. Another theory is the virus mutated, making the vaccine-induced immunity less effective.
The Bentley student, who lives off campus, has recovered, college spokeswoman Michele Walsh said. The student was in class Feb. 23 while ill, but all those who came in contact with the student were immunized, and no one else came down with the mumps, Walsh said.
The UMass student sought treatment for her symptoms Sunday, and her mumps infection was confirmed Tuesday. She, too, was fully immunized.
UMass has identified 27 people who were exposed to the student and is working with the Boston Public Health Commission to determine their immunization status, Pomales said. But no further illnesses have been reported.
Pomales said there is no reason think the student’s illness had any connection with another mumps case on campus, when a hockey player from the University of Southern Maine was found to have been contagious while visiting UMass on Feb. 20.
Mumps outbreaks have occurred on other campuses throughout the country this year. Indiana University had nine cases, and Butler University had 17, according to health officials in Indiana.
“What we’re seeing here in Boston is no different from the kinds of things that have been going on across the country for several years now,” said Dr. Benjamin Kruskal, chief of infectious disease and travel medicine at Atrius Health, a Massachusetts medical practice.
About 12 percent of the time, the vaccine fails to protect, Kruskal said. “When you expose lots of people, that 12 percent adds up to cause an outbreak,” he added.
Mumps is a viral infection that was a common childhood disease before a vaccine was introduced in 1967, but today only a few hundred cases occur nationally each year. The disease is best recognized by the puffy cheeks and swollen jaw that result from swollen salivary glands. Other symptoms include fever, headache, muscle aches, and fatigue. The virus spreads through coughing or sneezing, sharing utensils, and touching surfaces where infected mucus or saliva droplets have landed.