In Harvard Mumps Outbreak, All Affected Were Vaccinated

More than 40 people at Harvard University have been sickened by a mumps outbreak that began in late February — despite the fact that all of the students affected had been vaccinated against the virus.

While the United States usually sees anywhere from several hundred to a few thousand cases of mumps every year, outbreaks are far more likely to occur in populations of people living in close proximity to one another, like college dorms. As Dr. Amesh Adalja, an infectious-disease specialist and a senior associate at the University of Pittsburgh Medical Center's Center for Health Security recently explained, "The exposure that [the infected] have to mumps is so high in these situations that it overcomes the ability of the vaccine to protect them. It may be that, in these special situations, a much higher level of antibodies [against mumps] is needed to keep the virus at bay."

The virus is spread through saliva — in fact, the telltale puffiness of the cheeks in the vast majority of sufferers is caused by swelling of the salivary glands — and anyone infected can be contagious for up to 48 hours before the typical symptoms like headache, fatigue, fever and loss of appetite appear.

Sourced from: Live Science, Mumps Outbreak at Harvard: Why Do Vaccinated People Get Sick?