• The WHO defines polio or poliomyelitis as “a highly infectious viral disease, which mainly affects young children.” 

  • It is a crippling and potentially deadly disease that affects the nervous system

  • Polio may cause disability and also is a life-threatening disease, caused by the poliovirus

  • The virus is transmitted by person-to-person and spread mainly through the faecal-oral route (contaminated water or food). 

  • The virus multiplies in the intestine and then invades the nervous system and can cause paralysis.

  • There is no cure of the disease, only immunisation is the cure

  • Polio vaccine protects children by preparing their bodies to fight the poliovirus. 

  • There are two types of vaccines that can prevent polio: 

  • Inactivated Poliovirus Vaccine (IPV) which is injected in the leg or arm, depending on the patient’s age. 

  • Oral poliovirus vaccine (OPV) is given orally at birth, then primary three doses are given at 6, 10 and 14 weeks and one booster dose at 16-24 months of age.


  • The last reported case of type 2 wild poliovirus was in October 1999, leading to its global eradication declaration in 2015.

  •  However, vaccine-derived poliovirus (VDPV) outbreaks are predominantly caused by type 2 virus found in oral polio vaccines.

  • Around 40% of vaccine-associated paralytic poliomyelitis (VAPP) cases are caused by type 2 oral polio vaccine, despite the eradication of type 2 wild poliovirus.

  • The Global Polio Eradication Initiative (GPEI) has not reported VAPP cases during the 34 years of polio eradication efforts, and the Indian government does not consider VAPP as a form of polio due to its sporadic nature and minimal threat to others.

  • However, a 2014 report in the International Journal of Infectious Diseases revealed an increasing trend in VAPP-compatible cases in India from 1998 to 2013, outnumbering wild poliovirus cases since 2004.

  • The estimated incidence rate suggests that 50-100 children in India might experience VAPP each year, even though there is no official record of VAPP cases in the country.

  • To prevent type 2 vaccine-derived poliovirus cases, a global switch from trivalent to bivalent oral polio vaccine (OPV) took place in 2016. Additionally, one dose of inactivated polio vaccine (IPV) was introduced.

  • The Strategic Advisory Group of Experts on Immunization (SAGE) stated in 2015 that this switch, along with IPV introduction, would reduce and eliminate vaccine-derived type 2 poliovirus cases.

  • Contrary to expectations, the number of vaccine-derived type 2 poliovirus outbreaks increased significantly after the switch to bivalent OPV. In 2017, two countries reported outbreaks causing 96 VDPV type 2 cases, which increased to five outbreaks in 2018.

  • In 2019, 251 VDPV type 2 cases were reported from 15 countries, peaking at 1,081 cases from 26 countries in 2020. In 2021, 682 cases were reported, and 675 cases in 2022.

  • A type 2 novel oral polio vaccine (OPV), genetically modified to reduce the risk of reverting to neurovirulence, was authorized by WHO in 2020. 

  • However, as of May 2023, this vaccine has already caused three type 2 VDPV cases.

  • The novel vaccine, used only in type 2 VDPV outbreak situations, is considered safe and effective by available evidence, but it does not address VAPP cases resulting from continued use of oral polio vaccine.

  • Experts have appealed to the GPEI, donors, and global opinion leaders to transition to inactivated polio vaccine (IPV) in low- and middle-income countries and phase out the oral polio vaccine to prevent further cases of polio, including VAPP.



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Learnerz IAS | Concept oriented UPSC Classes in Malayalam: Polio UPSC NOTE
Learnerz IAS | Concept oriented UPSC Classes in Malayalam
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