Why in news?

A two-year-old child in Meghalaya’s West Garo Hills district tested positive for polio, a highly infectious viral disease that has been largely eradicated due to vaccination.

The Union health ministry clarified that the case is "vaccine-derived" and does not threaten India's polio-free status. However, officials remain vigilant to prevent any potential spread of the infection.

What’s in today’s article?

• Polio
• Vaccine-derived Polio

Polio

• About
  • Polio, or poliomyelitis, is a highly infectious viral disease caused by the poliovirus.
  • It primarily affects young children and can lead to severe health complications, including paralysis, muscle weakness, and even death.
  • The virus spreads mainly through contaminated food and water or contact with an infected person.
• Symptoms of poliovirus
  • While most polio infections are asymptomatic, a small percentage can cause paralysis by attacking the nervous system.
  • The symptoms can include fatigue, fever, headache, vomiting, diarrhoea or constipation, sore throat, neck stiffness, pain or tingling sensations in the arms and legs, severe headaches, and sensitivity to light, also known as photophobia.
• Types
  • There are three types of poliovirus: wild poliovirus type 1 (WPV1), wild poliovirus type 2 (WPV2) and wild poliovirus type 3 (WPV3).
• Polio in India
  • Polio was once a major public health challenge in India, with thousands of children affected by the disease each year.
  • India launched the Pulse Polio immunization program in 1995 to eradicate polio from the world.
    • The program was part of the Global Polio Eradication Initiative (GPEI), which was launched in 1988 by the WHO, national governments, and other organizations.
    • The program's goal was to achieve 100% coverage by administering polio drops to children ages 0–5 across the country on a single day.
  • Through mass immunization drives, known as Pulse Polio campaigns, and the relentless efforts of health workers, India successfully reduced polio cases dramatically.
  • India was officially declared polio-free by the World Health Organization (WHO) in 2014, after going three consecutive years without any new cases of wild poliovirus.
  • The country continues to maintain high levels of vigilance, with ongoing immunization efforts to prevent the re-emergence of the disease, particularly from vaccine-derived strains.

Vaccine-derived Polio

• About
  • Vaccine-derived poliovirus is a strain linked to the weakened live virus used in the oral polio vaccine (OPV).
  • While OPV is largely safe and has successfully eradicated polio in most countries, it can, in rare cases, cause the disease in children with weak immune systems.
  • According to experts, OPV can lead to vaccine-derived infections in two ways:
    • the weakened virus may circulate among children, eventually regaining its ability to cause severe infection, or
    • it can cause chronic infection in immunocompromised children, replicating in their gut and slowly regaining its virulence.
      • The recent polio case in Meghalaya appears to be an example of the latter.
  • It is easier to control further spread of such vaccine derived variants because the other children in the area are likely fully immunized.
    • One in every 150,000 children given the OPV in India is infected by it.
    • Even if children in an area where such a case is reported are completely vaccinated, health workers have to immunise them once again as a preventive measure.
• Detection of vaccine-derived polio cases in India
  • India’s last reported case of wild poliovirus (i.e. the infection caused by the naturally occurring version of the virus) was detected in West Bengal’s Howrah district in 2011.
  • India was declared polio-free in 2014 after successfully preventing any wild polio infections for three years.
  • However, during this period vaccine derived polio cases have continued to be reported.
    • An eleven-month-old immunodeficient child from Maharashtra’s Beed district succumbed to vaccine derived polio in 2013.
    • Multiple other cases of vaccine-derived polio have been reported from across the country, with the most recent case (prior to the one in Meghalaya) being reported in Kerala in July 2024.
  • These cases do not affect India’s polio-free status — only the detection of the wild poliovirus will change that.
• Injectable Polio Vaccine (IPV) as a tool to prevent the spread of vaccine-derived polio
  • The Oral Polio Vaccine (OPV) is highly effective in preventing the spread of poliovirus and has been central to the global polio eradication efforts due to its ease of administration.
  • However, in rare cases, OPV can cause the infection and spread it to others.
  • This has led some experts to recommend switching to the Injectable Polio Vaccine (IPV), which does not carry the risk of vaccine-derived polio because it contains no live virus.
  • However, IPV has its own challenges:
    • it requires trained personnel to administer, which could lower immunization rates, and
    • it does not prevent the transmission of the virus from person to person.
  • High levels of immunization are crucial to prevent outbreaks.
• Use of IPV in India
  • While countries like Canada and the US have fully adopted IPV, India uses both vaccines—IPV during routine immunization and OPV during Pulse Polio Days.
  • Experts note that India uses IPV sub-optimally, administering only one shot compared to the three shots and a booster used in other countries, necessitating the continued use of OPV to maintain immunity levels.