How Does the Immune System Remember Viruses?

When a virus enters your body, it is like an intruder breaking into your house. Your immune system sends out guards called antibodies to catch the intruder and throw it out.

After the battle, your body does not forget what the virus looked like. It takes a "photo" or a memory of that specific invader. This is stored in special cells called memory B cells.

If that same virus tries to attack again years later, those memory cells wake up quickly. They recognize the intruder immediately and produce thousands of antibodies much faster than before. Because the defense is so fast, you feel sick only once or not at all when you see an old foe.