What fraction of the afflicted had actually been vaccinated, e.g. with the MMR vaccine?
The mumps vaccine only has an 88% uptake rate and a booster is recommended for college kids but not required at Temple U.
I had all my kids boostered before leaving for college as well as the meningitis vaccine (neighbor’s daughter made paraplegic her freshman year), tetanus and pertussis and the Hep A and B. Two of them were heading into nursing so have to have all that stuff anyway.
I had the HPV done on them at age 12. The youngest was always wart prone and it cleared them up to. Found out later that this is not uncommon.