Polio is caused by one of three types of poliovirus from the Enterovirus genus. It spreads through contact between people, through nasal and oral secretions and through contaminated faeces. The polio virus can damage the brain and spinal cord. In around 98 per cent of cases it is a mild attack with almost no symptoms. However in a very small percentage of people, it can cause paralysis and loss of the use of a limb.
Polio has been around for thousands of years and affected human populations at relatively low levels till the early 1900s. This was a time when other diseases like diphtheria, typhoid and tuberculosis were being treated successfully. Ironically, advances in hygiene led to the increase of polio cases. This was because in the past, infants were exposed to the polio virus through contaminated water supplies at early ages. These exposed infants developed immunity due to natural maternal antibodies still circulating in their system. However, better sanitation meant that exposure to the polio virus was getting delayed till children had lost their maternal antibodies, which led to them being more vulnerable.
By 1940, polio was a highly infectious disease and many scientists were racing to make a vaccine for it.
It was Dr Jonas Salk who finally succeeded in 1955. He started working on a vaccine against the three strains of polio and tested the vaccine on his own children first. Salk’s vaccine was composed of an injected, inactivated form of the polio virus, which retained the ability to give Immunity against the disease without the risk of infecting the patient.
However, Salk’s vaccine was not completely effective against one of the three strains of polio and it only gave immunity for a limited time. In 1957, Albert Sabin, a Polish- American medical researcher, succeeded in making an oral vaccine which used a small amount of the live virus. This vaccine became available globally in 1962 and today, the oral polio vaccine is one of the most successful vaccines of all times.
Currently, the polio virus is only found in Afghanistan and Pakistan with an occasional spread to neighbouring countries.
Picture Credit : Google
