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.

There are three recognised scenarios in relation to herd immunity:

  1. The majority of the population are not vaccinated against a specific disease, however, a few people are ill and contagious. This can develop easily into a mass infection because the majority of the population are not vaccinated.
  2. Most of the population are not vaccinated against the specific disease but are well, some are vaccinated and healthy, and a few are not vaccinated, but ill and contagious. Mass infection can result again, but a small number of vaccinated individuals remain healthy and some that are not vaccinated will also be healthy.
  3. The majority of the population are vaccinated and healthy against a specific disease, a few are not vaccinated but well. A few are not vaccinated against the disease, and they are ill and contagious. The result is that the majority are protected due to the high level of vaccination. A few individuals will still become ill, but the large number of vaccinated individuals gives protection.
Following a vaccination, a person can become immune to the specific disease This immunity gives protection against illness in an individual.

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.

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.Data sourced from publichealthmatters.org (2015)A graph showing the Vaccine uptake.Data sourced from Public Health England's Green Book (2013)
Question

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

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.

Question

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

The measles vaccine was introduced in 1968 which 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.

Question

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.