Viruses that we've developed vaccines for, that have eventually been rendered inneffective due to a mutation? Is it a common occurence?
Generally the vaccines are moderately effective, but it's because we update them every year. If we didn't, they wouldn't be.
That being said there are efforts underway to make vaccines that would be more broadly effective against the flu and will be less susceptible to variants escaping ("universal flu vaccines"), and so this may not always be true in the future.
In the meantime, mRNA vaccines will likely be a huge aid for fighting the flu, because they can be manufactured rapidly for specific strains. Currently there's a six-month or longer lead time for inactivated- or attenuated-virus vaccines — which is what flu shots generally are — and sometimes new variants pop up or are discovered to be more infectious in between the manufacturing start date and that year's flu season.
Moderna apparently plans to make COVID booster shots that are also flu shots, although they may not be ready this year.
OK, this is the part I wasn't aware of. I assumed (dangerous, I know) that each year's 'new' flu vaccine was really just a new 'blend' of existing proven vaccines, for the most prevalent strains that year.
Edited to remove badly conceived question. New Question: How often do we have to develop novel vaccines for new Flu variants?
As I understand it predicting which flu strains to vaccinate this year is particularly hard because mask wearing/isolation/social distancing has reduced flu levels enough that they don't have a lot of data to base their predictions on
That being said, the process generally doesn't change — you still grow and kill (or grow and weaken) viruses the same way, you just start from a different base strain. For already-approved inactivated-virus flu vaccines, the FDA does not require new clinical trials for strain updates, and for already-approved attenuated virus vaccines, they only require very minimal trials (300 adults to prove adequate attenuation) [2]. So they're not novel in the sense of the COVID vaccines, which needed large scale clinical trials to prove efficacy — the flu vaccines have generally already proved efficacy, so for strain updates the most they need to prove is safety.
Another way of looking at this is that they're not new mutations that we scramble to develop and test vaccines for, we just roll out the same tried and tested vaccines, but we have to cobble together a different blend some years.
If the above is correct, then I guess the Flu example to answer my question would be: How often is a new variant of Flu (HxNy) discovered that necessitates a new vaccine being developed?