How do whole virus vaccines trigger immunity?
Because these vaccines are simply weakened versions of natural pathogens, the immune system responds as it would to any other cellular invader, mobilising a range of defences against it, including killer T cells (which identify and destroy infected cells), helper T cells (which support antibody production) and antibody-producing B cells (which target pathogens lurking elsewhere in the body, e.g. the blood). This immune response continues until the virus is cleared from the body, meaning there is plenty of time for memory cells against the virus to develop. Because of this, live attenuated vaccines can trigger an immune response which is almost as good as being exposed to the wild virus, but without falling ill.