​Answer

​During the primary infection the antibodies slowly increase, peak at around ten days and then gradually decrease. This primary infection results in the production of memory cells that remain in the bloodstream.

​Answer

​A second exposure to the same pathogen causes the white blood cells to respond quickly in order to produce lots of the relevant antibodies, which prevents infection.

The antibodies are produced so quickly by the memory cells that the pathogen is killed off before it can make the person ill. This is called being immune to a disease or having immunity.

​Answer

​Following a vaccination, a person can become immune to the specific disease. This immunity gives protection against illness in an individual.

Vaccinating the majority of the population against serious diseases can reduce the chance of people coming into contact with specific pathogens. This leads to herd immunity.