system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do some vaccines "last" longer than others? What's the difference?

I'm thinking of the flu - we need to get a flu shot every year because there's a different strain predicted to be the most prevalent, and because those strains keep evolving.

But then I think of, say, diphtheria. We only get that vaccine once or twice (by my recollection). Same for measles-mumps-rubella. Tetanus is only every 10 years.

What's the difference? Is it something about the diseases themselves that make them easier to vaccinate against, or is it something about the vaccines that make them generate longer-lasting antibodies?
gpt
The primary difference is the disease.  The Flu virus is more prevalent and it also mutates quicker than some other viruses, and so a vaccine that worked last year likely won't work this year as the virus has reproduced so much that it's too different from the previous version.