[resoluteteeth]

That's true in the sense that if you don't want to prevent people from getting influenza you don't have to give them a vaccine.

Otherwise, even if natural immunity to influenza lasts for a lifetime, most people don't get influenza very often (however people often confuse colds and influenza and don't realize this), so merely having a large existing number of strains would make it incredibly difficult to get natural immunity to all of them even if it wasn't continuing to mutate.

If you don't want people to be able to get influenza 10 times in their lifetime you would still have to give flu shots, and since their effectiveness decreases rapidly you would have to do this every year.

And that's assuming that natural immunity really lasts longer than flu shots.

Anyway that whole point is somewhat irrelevant to your original point that I was responding to that no other vaccines require boosters but it is clear based on your response that you are essentially engaging in circular reasoning (you don't think that boosters are required because no other vaccines require boosters, therefore flu vaccines are not boosters, therefore no other vaccines require boosters).