substance in a vaccine that stimulates the immune system
A vaccine stimulates the immune system to produce antibodies to fight a disease. Most vaccines are used to prevent infectious diseases caused by viruses, such as the flu, measles or polio. Cancer vaccines are used to: 1  prevent a cancer from developing (prophylactic, or preventive, vaccine). vaccine stimulates the immune system to produce antibodies to fight a disease. Most vaccines are used to prevent infectious diseases caused by viruses, such as the flu, measles or polio. Cancer vaccines are used to: 1  prevent a cancer from developing (prophylactic, or preventive, vaccine).