Immunisation (vaccination) is the safest way of creating immunity in humans and animals against certain diseases. Before vaccines were invented the only way to create immunity in the body was to tolerate a bout of the disease in question. Once endured, and providing you survived, your immune system could fight off any future infections of a similar nature before they took hold.

Immunity by vaccination is achieved by injecting small amounts of a killed or weakened micro-organism (or germ). These have been modified so that they can no longer cause the diseases against which they protect. This allows the body’s normal defences to build immunity against that particular disease. Vaccination has the same effect on the immune system so it is ready to fight off any future infections, but it hasn’t had to deal with the potential damage of the disease.

Some people think vaccine preventable infectious diseases aren’t a threat nowadays because they are rarely heard of. They are rarely heard of because of vaccination. It is one of the greatest public health achievements in history. Literally millions of premature deaths have been prevented, and countless children have been saved from serious illnesses, their complications and the permanent damage, both physical and mental, that can result.

While vaccines are much safer than actually having the disease, they, like all medicines can carry a small risk of adverse reaction. The majority of adverse reactions are very mild, but can, very rarely include post-vaccination Encephalitis. The risk of developing vaccine-related Encephalitis is extremely small in comparison to the health risks associated with the diseases that vaccines prevent. Importantly, the data indicates that vaccines are in the order of 1,000 to 100,000 times safer than running the risk of contracting the disease.

An Example

Measles - one in 5,000 children contracting wild measles will develop acute Encephalitis: 3 out of 20 of those children who develop Encephalitis will die from it and  20-40% of those who develop Encephalitis will be left with permanent after-effects. Less than one in a million children who had vaccination will develop Encephalitis from the vaccination which is less than the incidence of all types of Encephalitis.

In a study carried out in Finland between 1982 and 1986 of over ½ million children, it was found that the incidence of Encephalitis in the 3 months following a MMR vaccination was no different to the overall incidence.

There is no way of predicting who will have an adverse reaction to a vaccination. The individual’s susceptibility may be determined by their genetic background and previous immunological history. A checklist for contraindications is included in Guidance from the Department of Health.