Pathogens are microbes that cause diseases.

Vaccines allow a small quantity of dead or a weakened form of the disease-causing pathogen to be introduced into the body. This causes the immune system, to produce antibodies that are specific to the pathogen. Antibodies, which target and attach to the pathogen, destroy the pathogen.

The white blood cells then stop producing the antibodies specific to the pathogen and die. However, white blood cells called memory cells remain, and these can be produced very quickly if the immunised patient is exposed to the live pathogen.

Vaccines allow a dead or altered form of the disease-causing pathogen to be introduced into the body, which contain a specific antigen.

During the primary infection the antibodies slowly increase, peak at around ten days and then gradually decrease. 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.

During primary response, there is an antibody concentration rise over 7 days, dropping to just above zero by 20 days. During secondary phase a sharp rise levels off at a peak after 30 days.

Herd immunity

Following a vaccination, a person can become immune to the specific disease. This immunity gives protection against illness in an individual. The majority of the population must be vaccinated against serious diseases, which can reduce the chance of people coming into contact with specific pathogens, leading to herd immunity.

If the number of people vaccinated against a specific disease drops in a population, it leaves the rest of the population at risk of mass infection, as they are more likely to come across people who are infected and contagious. This increases the number of infections, as well as the number of people who could die from a specific infectious disease.

A graph showing the Vaccine uptake.Data sourced from Public Health England's Green Book (2013)

Describe the pattern of measles cases between 1950 and 1968, when the measles vaccine was introduced.

In 1950 approximately 380,000 cases of measles were detected. This shows that measles were regularly detected at approximately 600,000 cases per year in 1952, with some reductions to approximately 150,000 cases in 1954. Clear fluctuations are detected until approximately 1964.

The measles vaccine was introduced in 1968 which caused a sharp decline to approximately 150,000 cases in 1969.


Describe what happens to the number of measles cases after the introduction of the measles vaccines in 1968.

The introduction of the measles vaccine caused a sharp decline to approximately 150,000 cases in 1969.

A gradual decline was observed and in 1982 approximately 50,000 cases were recorded.


Explain how the introduction of the new MMR vaccine affected the cases of measles recorded.

A new MMR (measles, mumps, and rubella) vaccine was introduced in 1988, which caused a further sharp decline in recorded cases.

In 1994 the Measles/Rubella campaign was introduced, and then a second dose of MMR vaccination was introduced in 1996, which resulted in cases falling to almost 0 cases in 2004.