A two-year-old child in Tikrikilla (Meghalaya) has been infected with vaccine-derived polio. According to the Union Health Ministry, this is not a case of wild poliovirus, but an infection that presents in some people with low immunity.
Vaccine-derived poliovirus (VDPV)
- As per CDC, a vaccine-derived poliovirus (VDPV) is a strain related to the weakened (attenuated) live poliovirus contained in oral polio vaccine (OPV).
- The attenuated virus replicates in the intestines for a limited period and is excreted in the stool. If allowed to circulate in under- or unimmunized populations for long enough, or replicate in an immunodeficient individual, the weakened virus can revert to a form that causes illness and paralysis.
- OPV is a safe and effective vaccine that contains a combination of one, two, or three strains of live, weakened poliovirus, and is given in the form of oral drops.
- OPV has been instrumental in eradicating wild polioviruses around the world, including in India, because it stops the spread of the virus by inducing immunity in the gut.
- VDPVs emerge when not enough people are vaccinated against polio, and the weakened strain of the poliovirus from OPV spreads among under-immunized populations.
Poliomyelitis (polio)
- Poliomyelitis (polio) is a highly infectious viral disease that largely affects children under 5 years of age.
- The virus is transmitted by person-to-person spread mainly through the faecal-oral route. Three types – wild poliovirus type 1 (WPV1), wild poliovirus type 2 (WPV2) and wild poliovirus type 3 (WPV3) – have been known to exist.
- Symptomatically, all these strains are identical.
- Of the 3 strains of wild poliovirus, wild poliovirus type 2 was eradicated in 1999 and wild poliovirus type 3 was eradicated in 2020.
- As at 2022, endemic wild poliovirus type 1 remains in two countries: Pakistan and Afghanistan.
