There was uncertainty about acquired immunity and the behavior of different strains of COVID during the initial period. It was surprising that reinfection with COVID was common, with individuals experiencing multiple infections. Contrary to measles, where immunity is lifelong, coronaviruses including COVID only provide partial immunity upon reinfection, resulting in less severe symptoms. Older individuals are at higher risk during the first infection, but subsequent infections are milder until advanced age or weakened immune systems increase the risk of severe outcomes.