Poliomyelitis
About
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- Poliomyelitis (polio) is a highly infectious viral disease caused by the Polio virus which mainly affects young children.
- There are three wild types of poliovirus (WPV) – type 1, type 2, and type 3.
- Although symptomatically similar, genetic and virologic differences classify them as distinct viruses, each requiring separate eradication efforts.
Transmission
- Poliovirus is very contagious. The virus is transmitted by person-to-person spread mainly through the fecal-oral route or, less frequently, by a common vehicle (e.g. contaminated water or food) and multiplies in the intestine, from where it can invade the nervous system.
Characteristics of the disease
- Initial symptoms are fever, fatigue, headache, vomiting, stiffness of the neck and pain in the limbs.
- One in 200 infections leads to irreversible paralysis (usually in the legs).
Prevention and Treatment
- There is no cure for polio, it can only be prevented by immunization.
Polio vaccine
- There are two vaccines used to protect against polio disease, oral polio vaccine (OPV) and inactivated poliovirus vaccine (IPV).
| Oral Polio Vaccine (OPV) | Inactivated Poliovirus Vaccine (IPV) | |
| Form | Administered orally as liquid drops. | Given as an injection. |
| Composition | Contains weakened (attenuated) live virus strains. | Contains inactivated (killed) poliovirus strains, which cannot cause disease. |
| How it works | OPV contains weakened but live poliovirus strains that stimulate an immune response in the gut, where the virus typically multiplies. This vaccine is effective in stopping transmission within communities. | IPV triggers an immune response in the bloodstream, providing strong protection against paralytic polio. |
| Advantages | Easy to administer, provides community-level protection, and is more cost-effective. | Safe with no risk of vaccine-derived infections. |
| Limitations | In rare cases, the weakened virus can mutate and cause vaccine-derived poliovirus (VDPV), leading to outbreaks in under-immunized communities. | More expensive and requires trained healthcare workers for administration. It does not stop the transmission of the virus in the community as effectively as OPV. |
Polio eradication
- In 2014, India was officially declared polio-free, along with the rest of the South-East Asia Region.
- In 2015, wild poliovirus type 2 was declared as globally eradicated, followed by the official global eradication of wild poliovirus type 3 in 2019.
- With two of the three wild polioviruses eliminated, only type 1 wild poliovirus is still in circulation and is restricted to rural pockets of just two countries — Afghanistan and Pakistan.
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