Two vaccinations are not enough to guarantee protection against the mumps, according to a study published today in The New England Journal of Medicine.

The study, conducted by the Centers for Disease Control and Prevention and state health departments, examined a 2006 outbreak of the disease in the United States that affected college campuses from Kansas to Virginia.

Within a subgroup of patients, the study found, 83 percent were college students. In eight Midwestern states where the outbreak was most severe, 63 percent of all patients — and 84 percent of 18-to-24-year-olds — with a known vaccination status had received two doses of the mumps vaccine.

Health officials have long recommended two shots. The University of Southern Maine, in response to two cases of the mumps there last year, barred from its campus students who had not been doubly vaccinated.

The new study calls for either a more effective vaccine or a change in policy.

A third shot may be the answer for college students, and possibly everyone, an epidemiology professor told the Associated Press. —Sara Lipka