[a_c_s]

What you're describing isn't "the flu".

12-24 hours seems more like a "stomach flu" (Gastroenteritis) or a cold (rhinovirus), neither of which is influenza (aka "the flu").

According to the CDC: "Most people who get influenza will recover in several days to less than two weeks, but some people will develop complications as a result of the flu."

As others have covered and explained better than I can, the immune system isn't a muscle that needs an annual workout, especially given the risks of serious complications like pneumonia.