A mumps outbreak at Harvard University has tripled in size since mid-March, with 40 cases confirmed since the beginning of the year, according to the state Department of Public Health.
As of Monday, 11 students remained in isolation, university spokeswoman Lindsey Baker said.
This year’s Harvard outbreak tops the last big mumps cluster in Massachusetts, when 39 confirmed and probable cases were recorded at Boston College in 2013.
The Harvard Crimson reported Tuesday that Dr. Paul J. Barreira, director of Harvard University Health Services, expressed worries the outbreak might affect commencement.
But Baker said Harvard does not expect to make changes to its commencement plans because of the illnesses. Barreira was merely cautioning that individual students may miss out on the graduation ceremony and other end-of-semester activities if they become ill and have to be isolated, she said.
Although mumps cases have been reported at other universities, Harvard is the only one with such large numbers, said Scott Zoback, spokesman for the state health department.
Statewide, 67 cases have been reported since the beginning of the year, he said.
As of April 1, the US Centers for Disease Control and Prevention reported 467 mumps cases nationwide, but did not delineate how many were at universities.
Zoback said the infected students had all been vaccinated against mumps, as required by law. It’s possible the vaccine didn’t work in some people, or that the virus mutated in ways that made the shot less effective.
The mumps vaccine fails to induce immunity in about 12 percent of people who receive it, so mumps outbreaks occur occasionally even in highly vaccinated populations.
“This shows the importance of both personal protection and immunization,’’ Zoback said. “Immunization prevents a wider outbreak when we see periodic increases like this.’’
Mumps is spread through saliva — by coughing or sneezing; sharing utensils or cups; or handling objects touched by a sick person. Harvard has been urging students to wash hands frequently.
Barreira told the Crimson that students must “take seriously that they shouldn’t be infecting one another. . . . The concern is that if there’s a spike this week, that means those students expose others, so now we’re looking at a potential serious interruption to commencement for students. Students will get infected, and then go into isolation.’’
Mumps cases have also been reported at Boston University, the University of Massachusetts Boston, Tufts University, and Bentley University, as well as colleges and universities in other states.
For example, Indiana health officials have confirmed 22 mumps cases at Indiana University in Bloomington, 24 at Butler University in Indianapolis, five at Indiana University-Purdue University Indianapolis, and eight at Purdue University in West Lafayette.
Mumps symptoms include puffy cheeks or jaws from swollen salivary glands, as well as fever, headache, muscle aches, and fatigue.
Felice J. Freyer can be reached at felice.freyer@globe.com.
