system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are so many NHL players suddenly coming down with illnesses like mumps?

Hasn't the mumps vaccine been around for years? How do so many players not have it?
gpt
Most vaccines don't necessarily give you lifelong protection. Which is why we technically should get booster shots as adults but few of us do.

In addition to that, overall vaccination rates for children are dropping. Because less kids are getting vaccinated, herd immunity becomes less effective. In the past, a lot of adults that didn't get booster shots were protected via herd immunity.