Vaccination

Vaccination prepares the immune system to respond to a pathogen before the body encounters it in the future. A vaccine introduces weakened pathogens or their antigens into the body. Antigens are molecules that the immune system can recognise as foreign.

The antigens stimulate white blood cells called lymphocytes. Some lymphocytes produce antibodies that specifically bind to the antigens. Others become memory cells, which remain in the body after the initial response.

Protection after vaccination

If the same pathogen enters the body later, memory cells recognise its antigens and allow a faster, stronger antibody response. The pathogen can then be controlled before it causes illness. Because memory cells remain in the body, they can provide long-term immunity.

Vaccination and disease spread

When vaccination prevents people from becoming infected, the pathogen has fewer opportunities to pass from one host to another. Vaccinating people can therefore help control the spread of disease as well as protect individuals.