It's almost as if our immune system has developed over millennia to protect us against, influenza viruses such as covid 19. Fascinating! In fact, vaccinated are more susceptible to reinfection, because vaccines are a half ditch attempt to replicate this long developed evolutionary feature that we already possess as animals. Good thing the vaccines were forced on the population to reduce our ability to defend our own immune systems, effectively making our own biological systems a pay to play service!