Vaccination Against Polio

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Polio was, before the development of its vaccination, a major global concern because of its ability to disable and even kill patients. This article takes a quick look at the disease and how it is now vaccinated against.

What is polio?

Polio, also known as infantile paralysis or poliomyelitis is a severe disease caused by an extremely contagious virus called the poliovirus. Polio was actually one of the major childhood epidemics faced by people across the world in the 20th century, and these outbreaks have seriously disabled thousands of young children.

Poliovirus makes its way into us through the mouth and, like many other viruses, survives by hijacking cells and using their resources to replicate the virus. The virus is extremely infectious and makes its way into any cells it encounters on the way to the stomach and gastrointestinal tract. Eventually the virus makes its way into our blood and is spread throughout the body. In some severe cases, the poliovirus makes its way into the nervous system causing an inflammation of parts of the brain like the meninges, a protective layer between the brain and skull.

In some cases the virus makes its way into nerve fibres and destroys the cells responsible for carrying signals from our brain to our muscles. These are called motor neurons, and once damaged the muscles involved can no longer respond to signals from the brain, resulting in paralysis.

The symptoms of polio vary, but include the onset of a severe headache, high fever, muscle weakness, stiffness in the neck and back caused by inflammation, muscle pain, irritability, difficulties in normal bladder and bowel function, and sensitivity to any contact. Between one and ten days from the onset of these symptoms, paralysis sets in, and the extent of paralysis increases as the patient grows older.

There are actually a number of different poliovirus strains, each of which has a different effect on the body. Symptoms can vary according to strain, but fortunately modern vaccination can account for these variants to provide all-round protection against polio.

Vaccinating against polio?

The introduction of polio vaccines has very much changed the profile the disease and drastically reduced the number of cases observed every year. There are two vaccines in use against polio the first being an inactivated vaccine developed in 1955 named after its inventor, Jonas Salk, the second being an oral, live vaccine.

A live vaccine is made up of specially grown, weakened versions of the disease causing virus. This has the benefit of inducing a strong immune response against the virus and conferring lasting immunity against the disease in question. Inactivated vaccines have the distinct advantage of being safer than live vaccines as dead versions of the virus are used, however, the disadvantage is that many injections are needed (called boosters) to effectively immunise a person against the disease.

Both vaccines work on the basic principle of all immunisation. An element of a pathogen or the pathogen itself in a weakened or dead state, in this case poliovirus, is introduced to the human body to induce a defensive immune response. The immune system learns from this exposure, and develops a reservoir of memory cells that allow for a rapid response to any further infections.

Because the nature of polio transmission is limited to human beings, the hope is that with enough vaccination across the world the disease can be eliminated all-together. It is estimated that about 95% of children need to be immunised against polio for the disease to be eliminated.

When is the polio vaccine given?

Polio is usually administered as part of a combination vaccine here in the UK. That means that a single injection with multiple vaccinations is given, and one of the vaccinations in that single injection is against polio.

The first polio injection is offered to children at 2 months of age. At this point antibodies, important immune molecules, inherited from the mother begin to leave the body leaving a baby vulnerable to illness. At this point the DTaP/IPV/Hib injection is administered, an injection also referred to as the 5-in-1 which confers immunity against 5 diseases including polio.

A second dose of the 5-in-1 injection is provided at 3 months of age, and a third at 4 months of age. These additional doses are called booster shots and are needed for additional immunity against the condition in question.

Children are given another round of booster shots before they go to school as at that point they are at particular risk of being exposed to a variety of different diseases. At about 3 years of age children in the UK are given another booster against polio in the 4-in-1 DTaP/IPV injection. Finally a teenage booster is given anytime between 13 and 18 years of age, and this is a single, 3-in-1 jab immunising against polio, diphtheria, and tetanus.

In concert this immunisation programme works very well to protect children of all ages against polio, and saves countless children every year from a potentially fatal disease.

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