In this photo taken Wednesday April 6, 2016 students walk past the historic Thompson Hall at the University of New Hampshire in Durham, N.H. The water system serving the University is among more than two dozen in New Hampshire that have exceeded the federal lead standard at least once in the last three years. (AP Photo/Jim Cole)
In this photo taken Wednesday April 6, 2016 students walk past the historic Thompson Hall at the University of New Hampshire in Durham, N.H. The water system serving the University is among more than two dozen in New Hampshire that have exceeded the federal lead standard at least once in the last three years. (AP Photo/Jim Cole) Credit: Jim Cole

Four cases of the mumps have been confirmed at the University of New Hampshire in the past two weeks, state health officials said.

Two other students may also have been infected, officials said Friday. Officials said the six students were in close contact of each other and there is no sign of a wider outbreak, WMUR-TV reported.

All students had been vaccinated but it’s still possible to develop the mumps, officials said. Health officials are making a third dose of the vaccine, which has been shown to boost immunity, available to some other students who have contact with the infected students.