Vaccine

A vaccine introduces a small quantity of dead or inactive forms of that pathogen into the body. These cannot cause the disease in the same way as the active pathogen, but their antigens can still be recognised by white blood cells.

In the form specified here, a vaccine contains a small amount of the inactive pathogen. It cannot cause the disease, but it still carries the antigens needed to stimulate a specific immune response. The act of giving the vaccine is vaccination; the resulting protection is immunisation.

Vaccines and medicines help to combat communicable disease, but they do not all have the same purpose. A vaccine is mainly used before infection to prevent disease by preparing the immune system. Antibiotics and antivirals are used to treat particular kinds of infection, while antiseptics help prevent microorganisms entering tissues through places such as cuts.

Rather than waiting for a dangerous pathogen to infect the body, a vaccine introduces a safe form of the pathogen, or material carrying its antigens. Depending on the vaccine, the pathogen may be dead, inactive or weakened. The important point is that its antigens can stimulate an immune response without causing the disease the vaccine is designed to prevent.