Polio Vaccination: Understanding Risks, Benefits and Global Eradication Efforts - Dr Aparna Chakravarty

Poliomyelitis or Polio (in short) is a highly infectious viral disease caused by the wild poliovirus (WPV). WPVs (types 1,2,3) spread rapidly by saliva and stools of infected children.

Polio infection is silent in vast majority while 1 in 200 may develop sudden paralysis, usually of the lower limbs. The pathology is the spinal cord nerve cells controlling the muscle movement is damaged or destroyed by the polio virus. Infection can be fatal if the muscles of respiration are paralysed.

Polio used to occur in all countries, poor and rich alike. Hygiene, sanitation and safe water did not control it. Vaccination was the only solution.

Prior to introduction of polio vaccine in 1978, India had estimated 2,00,000 polio cases annually. A great progress has been made since then and India won a landmark victory in the long-drawn war on polio on 13 January 2011.

Polio Vaccination in India

India began its vaccination program against polio in the 1970s as part of the Expanded Programme on Immunization (EPI).

• In 1995 the National Immunization Day (NID) was launched, commonly known as the Pulse Polio Immunization program. This initiative aimed to administer polio drops to children aged 0-5 years twice a year. Additionally, multiple rounds (at least two) of sub - National Immunization Days(SNIDs) have been conducted over the years in high risk states/areas.

• In 1997, case-based polio surveillance started with support from WHO-National Polio Surveillance Project (WHO-NPSP). Surveillance for detection of polio virus transmission is being done through acute flaccid paralysis (AFP Surveillance) with laboratory network since then.

Success Story:

India's strategic fight against polio is a testament to its public health policy against vaccine-preventable diseases. The country reported its last polio case from Howrah, West Bengal, on January 13, 2011. India received "Polio-free certification" from the World Health Organization (WHO) on 27 March 2014.

Vaccination Efforts:

Over 170 million children are immunized during each NID, and 77 million during sub-national immunization days (SNID).

• India joined 125 other countries to introduce Inactivated Poliovirus Vaccine (IPV) into routine immunization as part of Polio Eradication and Endgame Strategic plan in 2015.
• India switched from trivalent Oral Polio Vaccine (tOPV) to Bivalent Oral Polio Vaccine (bOPV) in 2016 to maintain its polio-free status. The tOPV-bOPV switch process was critical step in the polio eradication endgame strategy.

India has innovated many strategies to overcome challenges in the polio eradication program – from vaccinating hard-to-reach populations through community microplanning and empowering. These strategies pioneered in India are being used to eliminate wild polio from Pakistan and Afghanistan, the final two endemic countries for wild poliovirus.

Eligibility:

At present in routine immunization, bivalent oral polio vaccine (bOPV) drops are being provided to all children less than five years of age and Inactivated Polio Vaccine (IPV) to children less than one year of age.

Vaccine Types:

In the 1950s Jonas Salk created the ‘inactivated poliovirus vaccine’ (IPV), followed by Albert Sabin’s live ‘oral polio vaccine’ (OPV).

Inactivated Poliovirus Vaccine (IPV): Introduced in 1955, IPV is administered by injection and is made from killed poliovirus strains of all three types (type 1, type 2, and type 3).

Oral Polio Vaccine (OPV): A live attenuated vaccine given orally, OPV has been widely used in India. OPV has been a vital tool in the global eradication efforts. Till recently, a mixture of the three types – ‘trivalent’ OPV (tOPV) – was used. There was a global switch in 2016 by ‘bivalent’ OPV (bOPV) with types 1 and 3 as WPV2 was eradicated in 2015.

Vaccine Safety: Both IPV and OPV are generally safe. Mild redness or pain may occur at the injection site for IPV. There is a very rare risk of vaccine-associated paralytic polio (VAPP) with OPV.

Global Polio Eradication Initiative (GPEI): Launched in 1988, GPEI is a partnership led by national governments, WHO, Rotary International, CDC, UNICEF, GAVI and the Bill & Melinda Gates Foundation.

Current Status: Wild polio cases have been reduced by over 99.9% globally. WPV type 3 was eradicated in 2019. WPV type 1 is still endemic in Pakistan and Afghanistan.

Circulating vaccine-derived polioviruses (cVDPV) remains a concern when in rare instances an excreted vaccine-virus (OPV) can genetically change into a form that can paralyse. The lower the population immunity, the longer this virus survives and the more genetic changes it undergoes.

In November 2020, the World Health Organization (WHO) granted Emergency Use Listing for novel OPV2 (nOPV2), designed to be more genetically stable than the Sabin strain and less likely to revert to neurovirulence.

Challenges: Under-immunized communities are at risk of outbreaks and vaccine misinformation can derail immunization efforts. Ongoing AFP and environmental surveillance are crucial for achieving global eradication.

In conclusion, India's journey towards polio eradication is a remarkable success story. However, we must remain vigilant, continue vaccination efforts, and work collectively to achieve a polio-free world.