- Polio, or poliomyelitis, is a disabling and life-threatening disease caused by the poliovirus.
- The virus spreads from person to person and can infect a person’s spinal cord, causing paralysis.
- Poliovirus is very contagious. It is transmitted by person-to-person spread mainly through the faecal-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.
- There is no cure for polio, it can only be prevented by immunization.
Types and Vaccines
There are three wild types of poliovirus (WPV) – type 1, type 2, and type 3. There are two vaccines used to protect against polio disease, oral polio vaccine and inactivated poliovirus vaccine.
- The oral polio vaccine (OPV) involves a weakened poliovirus which is orally administered. It is used in many countries to protect against polio disease and has been essential to the eradication effort.
- Inactivated Poliovirus Vaccine (IPV) involves an inactivated (killed) poliovirus administered via injection.
Vaccine-derived poliovirus (VDPV)
- When a child is immunized with oral polio vaccine, the weakened vaccine-virus replicates in the intestine for a limited period, thereby developing immunity by building up antibodies.
- During this time, the vaccine-virus is also excreted. In areas of inadequate sanitation, this excreted vaccine-virus can spread in the immediate community, before eventually dying out.
- On rare occasions, if a population is seriously under-immunized, the vaccine-virus can genetically change into a form that can paralyse – known as a vaccine-derived poliovirus (VDPV) which causes Vaccine derived Polio.
- VDVP are usually observed in children with primary immunodeficiency. Such children are unable to mount an immune response and are, therefore, unable to clear the intestinal vaccine virus infection.
- This condition doesn’t happen with Inactivated Poliovirus Vaccine as it doesn’t contain live viruses. IPV involves an inactivated poliovirus administered via injection.
Eradication of Polio
- Wild poliovirus type 2 and Wild poliovirus type 3 have been declared as eradicated worldwide in 2015 and 2019 respectively.
- Type 1 wild poliovirus is still in circulation and is restricted to Afghanistan and Pakistan.
Why in the news?
- Several states have launched the Intensive Pulse Polio Immunization (IPPI) drive.