Current scenario of polio vaccine & polio free world by 2018

Dr Khangembam Sachikumar *

Pulse polio immunization programme underway at Moreh Primary Health Centre with ADC, Moreh Robert Kshetrimayum on February 22 2015 :: Pix - Hueiyen Lanpao

The World Health Organization declared India – among other 10 countries in South East Region – as 'polio-free' in 2014. Since then, Government of India (GoI) has scaled up its initiatives against polio end game which targets virus eradication and sequential withdrawal of type 2 virus from oral polio vaccine (OPV).

However, prior to choosing the switch from trivalent OPV (t-OPV) to bivalent OPV (b-OPV), it was suggested to include inactivated poliovirus vaccine (IPV) in the national immunization schedule. The GoI declared introduction of single dose of intramuscular IPV at 14 weeks since October 2015.

Oral polio vaccine

It is a trivalent vaccine consisting of a suspension of attenuated poliovirus type 1, 2 and 3. It is the main weapon in the fight against wild polio virus.

What is Vaccine Derived Polio (VDPV)?

It is rare but documented strain of Polio which emerged in the guts of children with immunodeficiency or in population with very low immunity. It can cause paralysis in children. In 2011, eleven cases and in 2012 one case were detected in India. Worldwide, during 2000 to 2011, 20 out-break occurred in 580 polio cases. 33 cases of immune-deficient VDPV have been documented.

What is Vaccine Associated Polio (VAP)?

Those cases which have residual weakness 60 days after onset of paralysis and from whose stool sample vaccine polio virus is isolated or in a vaccine recipient within 4-40 days of receiving OPV.

Should the use of OPV be stopped?

It needs to be stopped for three reasons
o VAPP
o Outbreaks of Circulating VDPP
o Immunodeficiency can cause outbreak immune-deficient VDPP.

In order to eliminate VDPV, there is urgent need to introduce inactivated polio vaccine in sequential manner and switching Trivalent OPV to Bivalent OPV.

Inactivated Polio Vaccine (IPV)

It is a trivalent vaccine made of inactivated cell culture supernatants of three polio viruses. It is very safe. In post eradication era, IPV should be the automatic choice. Govt of India initiatives

Government of India (GoI) has taken following decisions regarding polio immunization during implementation of end game strategies in India:
o "Introduction of at least single dose of intramuscular IPV (IM-IPV) administration at 14 weeks or first contact afterwards in the RI along with 3rd dose of DTP in 6 states viz Bihar, Uttar Pradesh, Madhya Pradesh, Gujarat, Punjab and Assam.
o "Nationally coordinated switch from tOPV to bOPV all over the country on 25th April 2016 associated with cessation of use, withdrawal, destruction and validation of all available tOPV stocks from all over the country.
o " Introduction of fractional dose (0.1 mL) intradermal IPV (ID-fIPV) at 6 and 14 weeks in Orissa, Andhra Pradesh, Telangana, Tamil Nadu, Kerala, Karnataka, Maharashtra and Puducherry from April, 2016.

The main objective is to enhance population immunity against type 2 poliovirus just prior to proposed switch from t-OPV to b-OPV.

Risk following switching over from Trivalent Polio to Bivalent Polio
o Immediate time-limited risk of circulating vaccine-derived poliovirus type 2 (cVDPV2) emergence
o Medium- and Long-term risks of type 2 poliovirus re-introduction from a vaccine manufacturing site, research facility, diagnostic laboratory or a bioterrorism event
o Spread of virus from rare immune-deficient individuals who are chronically infected with OPV2

The current scenario

The IAP is recommending Three doses of IPV, given intramuscularly at 6, 10, and 14 weeks or Two doses at 8 and 16 weeks of age for primary immunization in its schedule.

The main aim of existing IAP guidelines on polio immunization is
To provide almost 100% protection against VAPP
To provide protection against type 2 poliovirus to naive children born post-switch,

Therefore, the focus would be protection against VAPP along with provision of protection against type 2 poliovirus by maximizing type 2 population immunity.

The threat of cVDPV type 2 emergence would be greatest, at least for one year following tOPV to bOPV switch.