>>11673090You're right. It's always influenza virus though. You don't develop resistance to influenza, you develop resistance to a serotype of influenza. Some viruses, like influenza, rhinovirus and coronavirus spin off serotypes rapidly enough to be seasonal. They run through society like a wave when conditions are right, then stay alive through much slower off-season spreading. During the rapid wave, millions of people are infected and the virus evolves against our immune response, eventually defeating it in several individuals through a sharp enough mutation to avoid detection even after a heavy immune response is mounted. The individual gets to experience an extra bad bought of the illness, and they spread a novel variant of the virus which might avoid the immune system in individuals who have already gotten the earlier serotype. If this bears out, this new serotype could be a winner for the next season rankings.
Coronavirus is notorious for rapidly spinning off serotypes. As of a month ago, there were already three major variants of covid-19. One of them, a later variant, is more infectious and deadly than the other two. It became the dominant variant over the last month by far. There are already likely several more variants yet to be sequenced and studied. When a variant is different enough to avoid the immune system in a previously infected person, it's a new serotype. Given the behavior of other coronaviruses, it's extremely likely that at least one new serotype already exists.
