[Editorial Analysis] Protecting against polio

Mains Paper 2: Health

Prelims level: VDPV

Mains level: Services relating to Health

Context

• The wild polio virus strains reduced by 99.9% since 1988.

• The world is inching towards eradicating polio. But unfortunately, more children today are affected by the live, weakened virus contained in the oral polio vaccine (OPV) that is meant to protect them.

• The weakened virus in the vaccine can circulate in the environment, occasionally turn neurovirulent and cause vaccine-derived poliovirus (VDPV) in unprotected children.

• While the wild-type virus has caused 22 and 25 polio cases in 2017 and 2018 respectively, in just two countries (Pakistan and Afghanistan).

• VDPV was responsible for 96 and 75 polio cases in more countries during the same periods.

• “Paradoxically, vaccination (using OPV) has become the main source of polio paralysis in the world,” notes a 2018 paper in The Lancet.

The VAPP burden

• The circulating VDPV strains are tracked, and outbreaks and cases are recorded and shared, little is known about vaccine-associated paralytic poliomyelitis (VAPP) cases, particularly in India.

• VAPP occurs when the virus turns virulent within the body of a recently vaccinated child and causes polio.

• The frequency of VAPP cases varies across countries.

• With high-income countries switching to the inactivated polio vaccine (IPV) that uses dead virus to immunise children.

• The VAPP burden is concentrated in low-income countries which continue to use the OPV.

• The WHO had suggested a rate of 1 case of VAPP per million births and had estimated the annual global burden of VAPP to be approximately 120 cases in 2002.

• Under these circumstances, India’s share would been merely 25 VAPP cases per year, based on the annual birth cohort of 25 million.

• The observed number of cases in India in 1999 was 181.

• This indicates that the actual risk is seven times the expected number.

• It is reasonable to assume that there would be 400-800 annual cases of VAPP globally.

• That would have meant that there were 100-200 VAPP cases in India each year.

• The global estimated incidence of VAPP was then revised to 200-400 cases.
Switching to IPV

• The reason for not switching over to the IPV is because global production was too low to meet India’s demand.

• India is the largest cohort. It needs 48 million doses per year to immunise all children.

• The IPV is essential for post wild-type polio virus eradication, to get rid of VDPV and VAPP.

• The globally synchronised switch from trivalent to bivalent OPV in mid-2016 was accompanied by administering a single dose of the IPV prior to administering the OPV.

• A single dose of the IPV given before the OPV prevents VAPP cases.

• A single dose of the IPV primes the immune system and the antibodies against the polio virus, seen in more than 90% of immunised infants.

• With no way of monitoring VAPP cases in India, there is no way of knowing if the use of a single dose of IPV followed by immunisation using bivalent OPV has led to a reduction in the number of VAPP cases.

Way forward

• Despite knowing that there is a higher burden of polio caused by oral vaccines, India continued to use the OPV.

• The decision to use only the OPV was faulty. Parents were obliged to accept the OPV and face the consequences of VAPP as well as VDVP.

• It is easier to administer the OPV than the IPV and the cost per dose of OPV is also lower than that of the IPV.

• However, the OPV fared poorly on two important counts: safety and efficacy.

• Administering the OPV was easier than the IPV but no cost-benefit analysis was done before choosing the OPV.

• Three doses protected only two-thirds of Indian children and many developed polio before they turned one year. So we had to give more doses per child.

• The high-income countries preferred the IPV, India and other low-income countries continued to rely on the OPV.

• India licensed the IPV only in 2006 but did not introduce it in routine immunisation.

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