Six weeks after Harvard University Health Services Director Paul J. Barreira first alerted Harvard affiliates of two cases of mumps, the total number of confirmed cases at Harvard has risen to 22, according to the Cambridge Public Health Department.

The new number is an increase of six from the most recent figure announced in late March, according to HUHS Spokesperson Lindsey Baker. The virus has affected students across campus, including members of multiple athletic teams who are currently in self-isolation for “presumed cases of mumps,” Barreira said in March.

The virus has also spread to nearby schools, including Boston University and Tufts University.

Ninety-nine percent of undergraduates have been vaccinated against the virus, according to Barreira. However, the vaccine is only effective 88 percent of the time, Anita M. Barry, the director of the Infectious Disease Bureau in the Boston Public Health Commission, said.

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Local public health regulations require that infected students be quarantined in isolated living conditions for five days. At the College, several students with the virus have temporarily relocated to the Harvard Inn. Inn residents received an email a few weeks ago from Dudley House Assistant Dean Christopher M. Gilbert, suggesting they may be able to move into upperclassman Houses to help provide more space for College students who may need emergency housing this semester.

Mumps is transmitted through salivary exchange, or respiratory droplets, fairly large particles that come out of people’s mouths and noses when they cough, shout, or otherwise forcefully expel air.

Barreira has directed students to take preventive measures that include refraining from sharing eating utensils, practicing hygienic habits like hand washing, and seeking medical attention at the onset of mumps-like symptoms.

As for a potential end to the Harvard mumps outbreak, Barry said last month that students’ departures from campus for the summer would slow transmission. She said the dense population and close proximity of students on a college campus makes it easier for mumps to spread.

According to Barreira, HUHS has been coordinating with the Massachusetts Department of Public Health, the Cambridge Public Health Department, and other schools to address the situation.

—Staff writer Menaka V. Narayanan can be reached at menaka.narayanan@thecrimson.com. Follow her on Twitter @mnarayanan97.