Despite the success of vaccines, mumps wasn't eradicated. Small pockets of infection continued to appear. These small outbreaks were difficult to control but eventually burned out such that they disappeared. For the most part, these isolated events were considered part of the ongoing reality of an ever-present virus.
Every day when I see patients in my surgical clinic, some are offered a procedure to help them feel better. Whether it is a minor surgery like a tonsillectomy, or something larger scale such as tumor resection, I have a full discussion with the patient regarding the benefits and risks of doing "something." Each time I go over the common minor risks of an intervention and the exceedingly rare, but potentially very serious risks that can occur. I also review with them the risks of doing "nothing" - of what may happen if they don't have surgery. Vaccination is no different.
Past generations of professional hockey players were never at risk of mumps outbreaks. Today's players are, and tomorrow's will be, along with adults generally. These outbreaks -- which the media portray as coming out of the blue -- don't surprise anyone in medical circles who has been paying attention.