Voluntarily........out of a job

Isn't that the reason we don't have a vaccine for 'common' influenza?
But we do, just different types each year. No vaccine protects against every variant and the virus continually changes. Each year they mix a different cocktail of variants to try to guess which will be most prevalent. Some years it’s 50% effective and in others it is 80% effective.

But it is always a moving target because the viruses change.