Diphtheria is a serious and life-threatening infectious disease. It is very infectious and can be passed on easily between people. Even with full medical treatment, it causes death in up to 1 in 10 of those who get it. Diphtheria is dangerous because the bacteria which cause it produce a powerful toxin (poison). The toxin kills cells in the mouth, nose and throat. The dead cells quickly build up and form a membrane which can attach to the throat and lead to death by choking. Diphtheria can also affect the heart (causing heart failure and death) and the nerves (causing neurological damage including weakness and numbness of limbs).
Before a vaccine was introduced in 1940, diphtheria used to be a common childhood illness which killed an average of 3,500 children a year in the UK. It is hardly seen in countries like the UK any more because of vaccination. However, the disease is still common in some parts of the world (for example, Russia, India, Africa, South East Asia and South America). Travellers to these areas can bring diphtheria back to the UK, which may put unvaccinated people at risk. Since the start of 2015, two unvaccinated children have died of diphtheria in Europe (one in Spain in 2015 and one in Belgium in 2016).