Original antigenic sin

Original antigenic sin is a way your body can remember certain germs it has seen before. When your body first sees a germ, it has to make special pieces called antibodies to fight it off. Antibodies remember the germ so if you get the same germ again, your body can use the antibodies to fight it off faster.

But sometimes, your body can get confused and use the wrong kind of antibody against the germ. This can make it harder to fight off the germ and make you sicker than if your body had used the correct kind of antibody. This is called original antigenic sin.