WHY ARE CASES OCCURRING AMONG SOME VACCINATED YOUNG PEOPLE, PARTICULARLY COLLEGE STUDENTS?
No vaccine is 100% effective. Mumps vaccine is 80% effective after one dose and 90% effective after two doses. That means, 10-20% of already-vaccinated people (depending on whether they had 1 or 2 doses) will not be immune and can still get the disease if exposed to the virus. Also, there are some states, such as Maryland, where K-12 students were not required to have mumps vaccine until the early 1990’s. These students are now in college and may be among the susceptible pool. If colleges don’t have a pre-entry requirement for 2 doses of MMR, up to 20% of those students may be susceptible. And even if all are vaccinated with 2 doses, at least 10% are probably still not protected. Also, college students are felt to be particularly at risk because of their living, learning and social environments. They may live in crowded conditions such as residence halls, where transmission occurs easily, similar to the usual viral respiratory illnesses such as colds and flu. They are also more likely
