Polio and post polio syndrome
The virus that causes polio (poliomyelitis) can damage the nerve cells that control your muscles, possibly causing paralysis and even death. But a worldwide vaccination programme has almost eliminated the disease. However, polio still occurs in some countries, and people who have had polio in the past may experience post polio syndrome decades later.
What happens if you are infected by polio?
There are three types of the polio virus: serotypes 1, 2 and 3. The virus can enter the human body through the nose or mouth and develops in the throat and intestines. From there, it invades the central nervous system, where it damages or destroys nerve cells known as motor neurons that control muscle movements.
Most people exposed to polio - about 95% - have only minor flu-like symptoms and do not realise they have polio. These symptoms include feeling or being sick, having a sore throat and headache, and having a high temperature, so the illness can easily be mistaken for flu.
However, for approximately 5% of people infected by polio, the virus enters the nervous system. These people will have symptoms that include a high temperature, headache, back and muscle pain, and a stiff neck - known as non-paralytic polio. In 1-2% of cases, motor neurons are damaged and this leads to paralytic polio, with symptoms that include weakness, muscle cramps and pain, and paralysis.
In bulbar polio, the brain stem is also affected, and people experience facial weakness, breathing and swallowing difficulties, and cardiovascular problems.
The damage to the motor neurons is distributed throughout the body and may not be noticeable, even though as much as 50% of these nerve cells may be destroyed or damaged. As the body begins to recover from a polio infection, half of the damaged cells will recover within a month. However other undamaged motor neurons may need to grow larger and work harder so they can make up for the damaged motor neurons.
How is polio preventable?
Vaccination can prevent polio, and a vaccination programme was introduced in the UK in 1956. In fact, the programme has been so successful that there are no new cases of polio reported in the UK today. The last case of natural polio infection occurred in 1984. This can be compared to 1955, when there were more than 6,000 notifications of polio in the UK. However, polio has not been completely eradicated and still occurs in some countries, so it is important to continue with the vaccination programme.
Until October 2004, people living in the UK were given a polio vaccine by mouth, but now it is injected into a muscle. If multiple injections are received based on a recommended schedule, the vaccine will almost always provide life-long protection. The vaccine is given as part of a combined product that also protects against other diseases such as diphtheria, tetanus and pertussis. These vaccines are inactivated, meaning they do not contain live organisms, and in most cases there are no reasons to avoid immunisation. The vaccination is safe for most people, including pregnant and breast-feeding women, in people with a minor illness such as a cold and in children with neurological complications such as spina bifida. Currently, routine vaccinations are normally given in the UK as follows:
- First dose, at 2 months old
- Second dose, at 3 months old
- Third dose, at 4 months old
- Pre-school booster, from 3 years and 4 months old (up to starting school)
- Booster, at age 14 years old
If for some reason a child or adult has not been given vaccines following the above recommended schedule, a GP can advise on current guidelines and ensure the person is appropriately vaccinated.