Herd immunity

Herd immunity is the protection given to a population against an outbreak of a specific disease when a very high percentage of the population have been vaccinated against it. It can therefore help prevent epidemics and pandemics.

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.

Governments and public bodies such as the NHS make decisions on who to offer vaccinations to. In order to do this, they assess the risk, cost and benefit. They consider problems such as the likelihood of side-effects as well as advantages such as savings from not having to treat serious diseases. The diagram below shows how successful childhood vaccines in the UK have been.

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.

Measles

Measles is a very infectious viral disease that is often caught by young children. It is transmitted through the air in tiny droplets after an infected person sneezes. It causes a fever and skin rash. Many children in developed countries are given vaccines against measles, but this is not the case throughout the world. Infection can cause more serious effects, eg infertility, in adults who did not catch the disease as children.

Computer-generated image of a measles (Rubella) virus
Computer generated image of a measles (Rubella) virus

All children are offered a number of vaccinations but not all parents choose to accept the offer because some are concerned about the risk of possible side effects. It is important that people have clear and unbiased information when making decisions.

A closer look at MMR

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.

In 1998 a study linked the MMR vaccine to autism - the results of the study could not be replicated by other scientists, which meant that they were not reproducible. Many scientific studies since then have found no link between the MMR vaccine and autism. The number of measles cases increased rapidly after the percentage of the population who had been vaccinated dropped from over 90 per cent to just over 80 per cent.

Question

Describe the pattern in measles notifications between 1950 and 1969, the year after the measles vaccine was introduced.

A graph showing the Vaccine uptake.

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 happened 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.

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