Vaccination

C. Vaccination : Vaccination is the administration of a vaccine — an inactivated pathogen or an antigenic portion of it — to protect against that particular pathogen. The immune system is usually efficient at keeping pathogens out or clearing them once they enter, but some pathogens can overwhelm it, particularly ones the body has never met before and so does not recognise.

How does vaccination work? Vaccination works by teaching the body to recognise a new pathogen before it ever causes disease: it stimulates the body to make antibodies against the pathogen's antigens and primes immune cells to remember those antigens, so that if the real pathogen is encountered later, the response is much faster. A vaccine achieves this by exposing the body to a safe version of the pathogen, which may take the form of a protein or sugar fragment from the pathogen, a dead or inactivated pathogen, a toxoid (an inactivated version of a toxin the pathogen produces), or a weakened (attenuated) live pathogen. When the body responds to any of these, it mounts a genuine adaptive immune response, which then equips it to fight off the real infection far more effectively if exposure ever occurs.

Vaccines are rigorously tested through many rounds of study before public use, and extensive evidence shows they are safe, with side effects that are typically rare and mild. Vaccination is an important form of primary prevention and has allowed diseases such as measles, polio, tetanus and whooping cough — once major killers — to be brought under control; because widespread vaccination also reduces the pathogen's ability to spread through a population, vaccination protects not just the individual but the wider community as well.