- A three-member team was constituted by Central Drugs Standard Control Organization (CDSCO) to investigate a recent case of type-2 virus contamination of polio vaccine.
- Recently a WHO-based surveillance of stool samples in UP, Telangana and Maharashtra has reported the presence of polio virus-2 strain.
- However polio virus-2 strain has known to have been eradicated from India in 2016.
- This polio virus-2 strain is known to have been induced by Oral Polio Vaccine that was administered as a part of National Immunisation Programme in these states.
- About 50,000 vials (1 vial=20 doses) of contaminated vaccine may have possibly been used in Uttar Pradesh, Maharashtra and Telangana.
Vaccine-induced Polio: A backgrounder
- Polio is caused by Polio Virus type 1,2,3 single stranded RNA virus Natural or Wild Polio Virus.
- There are three serotypes of poliovirus, each of which causes poliomyelitis.
- The virus enters the body orally and reaches the intestines before reaching the blood stream.
- Once it enters the blood stream it attacks the central nervous system damaging the cells and could paralyse the infected.
Polio vaccines: OPV and IPV
- Two polio vaccines are used to combat Poliomyelitis.
- The first includes an injected dose of inactivated (killed using formalin) polio virus (IPV).
- IPV provides immunity in the blood stream, preventing polio infection from progressing and protects the motor neurons.
- The second type of vaccine is OPV which is a live weakened version of the virus, which produce mutation in the viral genome causing immunity.
Vaccine-induced polio virus
- While oral vaccine uses a weakened virus, the injectable one uses an inactivated one.
- Besides OPV is easier to administer.
- Further OPV also causes immunity of the community as the children administered oral vaccine can cross-infect via faecal-oral route with the vaccine virus and naturally immunise others.
- However the OPV administered can also cause vaccine-derived poliovirus, leading to paralysis.
- Besides type 2 polio virus is associated with 90% of vaccine-derived poliovirus.
Global switch over from Trivalent (ToPV) to Bivalent Oral Polio Vaccine (BoPV)
- Historically OPV used under immunization programmes around the world has been trivalent oral polio vaccine ToPV that has three strains of live, weakened polio virus.
- However the last case due to type-2 wild poliovirus globally was reported from India in 1999.
- After this the WHO recommended the bivalent version BoPV with just two strains 1 and 3.
- Since 90% of vaccine-derived poliovirus is caused by type 2 polio virus, WHO recommended the switch from ToPV to BoPV.
Vaccine-induced Polio in India
- Polio was endemic to India till 2011. Since 2011 there were no reported cases in India and therefore India was declared polio-free by WHO in 2014.
- As of 2012 polio remains endemic in only three countries, Nigeria, Pakistan and Afghanistan.
- After World Health Organization declared India “polio free” in 2014, India switched from ToPV to BoPV under its polio vaccination programme in 2016.
- However there have been cases reported in India in 2013 onwards that few cases of Polio are due to vaccine-induced Polio Virus type 2 (VDPV).