Infectious disease Progress on eradicating polio has stalled.
Why there is a concern now:
- WHO has missed the target multiple times to eradicate Polio globally between 2000 and 2012 and now the world, it seems, is now caught between attempts to eradicate wild polio on one hand and the menace of vaccine-derived polio virus (VDPV) on the other.
- In 2013, a WPV1 outbreak was confirmed following importation in Dollo zone of the Somali region and worries that polio may travel back to countries which have already eradicated it, like India.
- Growing number of countries with cases of the disease that have been caused by a polio vaccine are attracting more notice as those caused by the wild virus itself have dwindled. In 2017 cases caused by vaccine-derived viruses overtook, for the first time, those caused by the wild version.
- Poliomyelitis or polio is a highly infectious disease caused by a virus.
- It invades the nervous system, and causes paralysis, medically known as an acute flaccid paralysis (AFP). Disease is characterised by sudden muscle weakness and pain in the limbs.
- The disease is transmitted from person to person, mainly through the faecal-oral route, affecting children under five years of age.
- In the absence of wild polio virus (WPV) transmission, India was declared a polio-free country in March 2014, after years of relentless vaccination.
There are three types of wild poliovirus (WPI):
- Type 1 causes paralysis in about 1 in 200 infections.
- Type 2 was last recorded in 1999.
- Type 3 is less virulent than type 1, causing paralysis in about 1 in 1000 cases.
- Of the three strains in which poliovirus exists, type 2 causes more than 90% of paralytic polio cases from mutated oral-vaccine strains.
About Polio Vaccine:
- Polio vaccines come in two forms.
- The injectable version, which rich countries use, contains dead viruses and creates antibodies in the blood. Someone vaccinated with it who ingests the wild virus (say, by drinking contaminated water) is protected from the disease. But, for several weeks afterwards, the wild virus in his gut can be passed on to people who are not immune.
- The oral polio vaccine, by contrast, contains weakened live virus. Because the antibodies it creates take up residence in the gut, they battle there with any wild virus a vaccinated person ingests, making further transmission less likely.
About Vaccine-Derived Polio?
- Oral polio vaccine (OPV) contains an attenuated (weakened) vaccine-virus, activating an immune response in the body. When a child is immunized with OPV, 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 (and this can offer protection to other children through ‘passive’ immunization), before eventually dying out.
Benefit of Oral Polio Vaccine
- The oral vaccine has another benefit. Someone vaccinated with it excretes the weakened form of the virus for a couple of weeks. Anyone who comes into contact with this excreted virus also gains immunity, and can pass it on further, to others who are not immune.
- In places with poor sanitation, this sort of passive vaccination is a boon—but only up to a point. As the weakened virus from the vaccine jumps from one unvaccinated person to another, the chances increase that something will go wrong. Along the way, the virus mutates and, after a year or so, can turn into a paralyzing form that resembles the wild virus.
- OPV is also cheaper and simpler to administer than IPV.
About Global Polio Eradication (GPEI)
- The Global Polio Eradication (GPEI) set up in 1988, when the World Health Assembly (WHA) passed a resolution to eradicate polio by the year 2000.
- It is the largest public health initiative ever in the history of global public health.
- The GPEI assumed the implementation of four basic strategies to achieve global polio eradication:
- High routine immunization of every child below 1-year-of age with at least three doses of Oral Polio Vaccine (OPV)
- National Immunization Days (NIDs) targeting children under 5 years’ old
- Sensitive surveillance systems and
- Mop up campaigns in areas where population immunity is low due to suboptimal routine immunization coverage and presence of cases that are compatible with polio.
Major Challenges in Polio Eradication:
- The challenges in polio eradication however seem to be more due to human and program-related obstacles rather than due to science
- In India the main obstacle had been the refusal of polio vaccine by certain communities on account of illiteracy and misinformation
- The drive for polio eradication still remains a challenge for Pakistan, Nigeria, and Afghanistan (the remaining polio endemic nations) due to incomplete vaccination coverage.
- The globe-trotting, multilateral, public-private partnership to ensure a “polio-free world” is sure to be the benchmark of all future public health programs. The polio struggle has also taught valuable lessons which will be useful to fight malaria, TB, HIV/AIDS, and all such diseases which humans desire to conquer.
- Strengthening routine immunization service delivery and assigning trained immunization focal points
- Instituting community-based surveillance using trained community volunteers in border areas and in the nomadic population to detect and notify cases in their area of residence
- Finally, surveillance and routine immunization, particularly in hard to reach areas, needs to be closely monitored in the region to be able to identify and understand the gaps in population immunity.