Herd immunity requires that the majority of people are vaccinated to stop proliferation of disease. Measles, for example, is so contagious that about 90 per cent of people who are not immune will become infected if they come close to an infected person.
However, childhood vaccination rates have been falling as anti-vaccine sentiment grows, particularly among the middle classes. ‘If enough parents opt out of vaccine programmes then the herd immunity system breaks down. It is not okay to assume that the risk of infection is negligible if everybody else does it. They might feel the same way,’ says Professor John Ashton CBE, former President of the Faculty of Public Health.
In the UK, as in the US, vaccination rates tend to be lower in more affluent areas, but Professor Ashton believes this is breaking the covenant that society should protect its most vulnerable. ‘Wealthier children who get measles are more likely to make good recoveries but poorer children who pick up the disease are more vulnerable to complications caused by malnutrition, overcrowding and lack of support. You should have your child vaccinated to protect everyone else’s child too.’
Diseases like diphtheria, a potentially fatal bacterial infection that causes a thick grey-white coating to appear on the back of the throat and leads to high fever and breathing difficulties, is still very rare in England because most people have been vaccinated against it. Before a vaccination programme was introduced in 1940 for babies aged two months, it was one of the leading cause of death in children in the UK.
This could change if vaccination levels drop since it is highly contagious and can be spread through the air or on bedding and clothing.