Updated 4:51 p.m. ET
Ohio State University's mumps outbreak is growing, with 40 people now infected, according to new numbers released by Columbus Public Health Friday.
That's up from 28 cases tied to the Columbus, Ohio university that were reported Tuesday.
Eighteen women and 22 men ranging in age from 18 to 48 are among those sickened. The vast majority of cases -- 32 -- are students, but also infected are four staff members, a student's relative, and three people who don't work or study at the campus but have links to the university community.
Three of the patients were hospitalized for at least one day then released.
Mumps is spread through droplets of saliva or mucus from the nose, mouth or throat of an infected person. It can be transmitted through sharing drinks or eating utensils, the Centers for Disease Control and Prevention notes.
The time between infection and symptoms can be anywhere from 12 to 25 days. Symptoms include fever, muscle aches, headaches and fatigue, before progressing into swelling of the salivary glands.
While Ohio and the university do not have policies mandating the MMR vaccine for incoming students and staff, health officials point out people can still develop mumps if they've gotten vaccinated. An FAQ sheet from the university and Columbus Public Health states for every 100 people vaccinated, 10 to 20 still risk getting the disease.
University spokesperson Elizabeth Cook told CBS News in an email the school has distributed posters encouraging healthy hygiene practices to residence halls, fraternity and sorority houses and off-campus neighborhoods. The school has emailed students, staff and faculty of the possibility of exposure and posted alerts on social media.
"While investigators continue to monitor cases, the university has taken steps to broaden awareness of the virus and is promoting best practices to protect the health and safety of the university community," she said.
Mumps can't be treated, and people typically recover within two weeks with help of supportive care. In rare cases, complications like brain swelling and deafness may occur.
Recent outbreaks took place in February among students at Fordham University in the Bronx, New York City and in 2009-2010 in New York City among school-aged children who had mostly been vaccinated, according to officials. In 2006 there was a mumps outbreak among mostly-vaccinated college students in the Midwest as well.
The CDC says these outbreaks often occur in crowded conditions such as on campus, or in close-knit communities.
The vaccine is very effective against preventing measles, mumps and rubella -- two doses are about 88 percent effective -- but it is not perfect, CDC spokesman Jason McDonald told CBS News in an email. While it is still possible for vaccinated individuals to get infected in intense exposure situations, he pointed out they tend not to get as sick.
"If they do get mumps, people who have been vaccinated are likely to have less severe illness than unvaccinated people with mumps," he said.