Your immune system stores a record of every germ it has ever encountered—in special cells called B cells and T cells, also known as memory cells. With this memory, your body can recognize and fight off those germs more easily the next time
Some viruses, like the flu and the common cold, have to be fought off repeatedly because they come in different strains and they change, or mutate, over time.
It is possible, experts say, that COVID-19 could become a seasonal illness, like the flu. Virologists call this an "endemic" disease -- one that is constantly circulating among us, just as the four existing "human" coronaviruses that are already in circulation.
In the years and decades to come, many people will be exposed to it in childhood and develop some immunity, which would protect them later in life against serious disease.