Nine students at the Tufts Somerville/Medford campus have been diagnosed with mumps, a university official confirmed Wednesday.

Students are required to be vaccinated against the disease — which causes fever, headaches and painful swelling of the salivary glands — before matriculating, but campus health officials warned it is still possible for them to contract the virus.

“University health officials have informed students, faculty and staff and are encouraging students to take precautionary measures and to be evaluated by the university’s Health Service if they believe they might have symptoms,” Patrick Collins, Tufts executive director of public relations, said.

The university is working with municipal and state health officials and will continue to closely monitor the situation, he added.

The first student was diagnosed three weeks ago and the virus has continued to spread.

Another outbreak this fall has infected 10 students across two liberal arts colleges in Maine — Bates and Bowdoin, Portland-based WCSH reported. In the spring, 16 students were infected in an outbreak that swept across Tufts, Boston University and Harvard campuses.

The recent outbreaks could point to a waning immunity given by the measles, mumps and rubella vaccine, according to a 2012 U.K. study by Joint Committee on Vaccination and Immunisation. Most people receive the vaccine as infants, with a booster around age 5, but as a person ages, the level of antibodies protecting them from the disease wanes.

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The study found protection from infection falls to around 60 percent after 10 to 15 years, noting a number of outbreaks among young adults at universities.

“A resurgence of mumps may be expected in that population in future years due to the decline in MMR coverage during the last decade,” the study said.

To protect themselves, students should take basic precautions like washing their hands, and covering their mouths and noses when they cough or sneeze, according to the university.