None of the Flyers has come down with the mumps, but it's too soon to breathe a sigh of relief.
So far, about 20 players on six NHL teams definitely or probably have gotten the viral illness, despite a flurry of vaccinations throughout the league. Among those afflicted is the Pittsburgh Penguins' Sidney Crosby, the league's most valuable player, who tested positive for the disease Dec. 13.
The Flyers have played three affected teams - the New York Rangers, Anaheim Ducks, and New Jersey Devils - within the incubation period of 16 to 18 days.
The mumps virus is transmitted through saliva released in a cough or sneeze.
Or a pounding, gasping body check.
"If I pass by one of these [infected] hockey players and they sneeze on me, maybe I get a moderate dose" of the virus, said Robert Bettiker, an infectious disease specialist at the Temple University School of Medicine. "But if I get slammed into the boards by one of them, maybe I get a larger dose."
Mumps usually causes nothing worse than fever, headache, fatigue, and chipmunk-cheek-like swelling of the salivary glands. Serious complications - notably meningitis, hearing loss, and swelling of the testicles - are uncommon, and even less likely in vaccinated people, according to the U.S. Centers for Disease Control and Prevention.
But the CDC also says the vaccine doesn't work for some people, the protective effect can wane over time, and there is no test that reliably predicts whether a person has immunity.
What's more, an infected person is contagious even without symptoms, which can take from two to three weeks to develop.
All of which shows why it is too soon for joy in Mumpsville, even though most of the Flyers were vaccinated after their 4-1 win over New Jersey on Dec. 11.
Bettiker, for one, got the recommended two-dose vaccine (which also protects against measles and rubella) as a child, but still got the mumps.
"I remember my cousin saying, 'My cheeks hurt,' " Bettiker said. "Two weeks later, I said the same thing."
The upside is that getting the mumps confers immunity against it.
In the United States, several hundred cases of mumps are reported each year, down from about 186,000 a year before vaccination became standard in 1967. However, the number can spike. In 2006, more than 6,500 cases were reported, most on Midwest college campuses.
During that outbreak, the CDC urged widespread vaccination of students, and reassured the schools that the immunization "is a very safe vaccine, even if the person has already had two [childhood] doses or has had the disease."