What makes Polio a dreaded disease?

The scariest thing about polio is that 95 percent of people infected with the polio virus do not exhibit any symptoms. Yet while they themselves do not display any symptoms, they can still spread the polio virus and cause others to develop polio.

The Poliovirus can strike at any age, but affects mainly children younger than three. It is spread by poor sanitation and infected drinking water. Early symptoms are fever, fatigue, headache, vomiting, stiffness and pain in the neck and limbs.

The poliovirus attacks the central nervous system, leaving victims with fever, permanent muscle weakness, paralysis and, in extreme cases, death from asphyxiation.The virus generally enters the body through the mouth and multiplies in the intestine. The polio virus in the nervous system can cause total paralysis in a matter of hours.

Polio is caused by three poliovirus serotypes-- Poliovirus type 1 (PV1 or Mahoney), PV2 (Lansing), and PV3 (Leon). Out of these Type-2 poliovirus appears to have has been eliminated.

Treatment of Polio focuses on providing relief of polio symptoms as the body fights the poliovirus. This is called supportive care.

If there is one disease that illustrates the value of vaccination, it is Polio. Typically the fight against Polio starts with building up the body’s immune system to fight the disease through immunization. Under the Global Polio Eradication Initiative -- the largest public health initiative the world has ever known, 130 million children around the world are immunized before the age of five.

When it comes to immunization there are only two options – oral drops (OPV) or injectable vaccine (IPV). Among these, the oral polio vaccine developed by Polish American scientist Dr. Sabin, has been preferred in many countries because it is administered orally -- usually on a sugar cube. This also does not require a highly trained person to administer the dose i.e. two drops in the mouth.

Dr. Sabin believed that the polio viruses lived in the small intestines. So he developed a mutant form that could not reproduce the disease, but would displace more lethal forms of the virus. Rather than subject another person to risk, Dr. Sabin ingested the mutant virus himself to prove its effectiveness.

The Salk vaccine on the other hand needs to be injected with a needle. These injections require administration by trained medical personnel. There is also resistance among poor, illiterate people to get their children “pricked by needles”.

One of shortcomings of the oral vaccine is that the attenuated virus used in the vaccine may revert to pathogenicity, causing paralysis in one out of every 750,000 to 2.5 million people vaccinated, depending on the source. Rarely, a strain of poliovirus in OPV may genetically change and circulate among a population. These are known as vaccine-derived polioviruses (VDPV) and knowledge on them is growing.

On the other hand,IPV is not a 'live' vaccine - the polio virus is inactivated - and immunization with IPV carries no risk of vaccine-associated polio paralysis. The injectable vaccine contains three viral strains in the following proportions: 40 units of type 1; 8 units of type 2; and 32 units of type 3. Generally speaking, the oral vaccine contains one live, attenuated strain of each type.

Because of these reasons alone in countries where the risk of wild-virus caused polio has come down to zero immunization programmes are now considering combined immunization schedule using both OPV and IPV.

In countries where there is only one type of virus in circulation (generally type 1, but also type 3), the WHO recommends using a monovalent vaccine). Monovalent oral polio vaccines (OPV) – targeted at poliovirus types 1 or 3 – appears to work faster than traditional trivalent OPV to build immunity.