In India, while no cases have been reported since 13 th January 2011 (last case from West Bengal), eradication activities are continuing strongly to secure the gains achieved. Large-scale immunization activities were conducted in March, and active surveillance for acute flaccid paralysis (AFP) cases is continuing. As such, reports of AFP cases is not unexpected or unusual – quite the opposite, in fact, it means disease surveillance is working. Every month, approximately 5,000 AFP cases are identified and investigated across the country. Symptoms of AFP are caused by a number of different pathogens, poliovirus being just one of many potential causes. Strong disease surveillance means that at least two AFP cases per 100,000 population (aged <15 years) are identified, to ascertain the presence or absence of poliovirus circulation in a given environment. The extensive immunization and surveillance activities ongoing in India will need to continue, as long as endemic poliovirus has not been eradicated in the remaining three countries – Pakistan, Afghanistan and Nigeria. The combination of high population immunity levels and strong disease surveillance is the best way for a country to minimize the risk and consequences of polio re-emergence or re-introduction. Kerala’s last case was reported in September 2000.
India’s name has been struck off the shame list and efforts have to continue so that it will not be included in the future. The World Health Organization (WHO) has taken India, which in 2009 had more polio cases than any other nation in the world, off its polio endemic list after not a single case of the crippling disease was reported for over a year. For the next two years, if India does not report any polio cases, it will be officially called “polio free”. Let us resolve to make India polio free by 2014.
Vaccine-associated paralytic poliomyelitis (VAPP) is a rare adverse reaction that can occur following vaccination with the live oral polio vaccine (OPV) – believed to be due to a loss of attenuating mutations and reversion to neurovirulence during replication of the vaccine virus in the gut. Risk of VAPP is lower in India, than in developed countries, because of high maternal antibody, birth dose of OPV, early immunization with OPV and the low ‘take’ of the vaccine. However, there is little good data on VAPP in India (181 cases reported in 1999) as most are reported as non-polio AFP.
A more recently recognized and unanticipated problem with OPV was the emergence of Vaccine Derived Polio Viruses (VDPV) which arise due to mutation and recombination of the vaccine virus in the gut producing a neurovirulent virus that is different (1-15%) from the parent vaccine virus and unlike VAPP, is transmissible and capable of causing outbreaks. They have been classified into 3 groups – circulating VDPV (cVDPV), VDPV in the immunodeficient host (iVDPV) and VDPV of ambiguous origin (aVDPV). VDPV have probably been present since the time OPV was first used but have been detected only now after sensitive surveillance systems have been developed.
India has reported its first case of vaccine derived polio virus (VDPV) infection of 2012. A five-month-old child from the Murshidabad district of West Bengal has got infected with the virus after taking the oral polio vaccine.
This, however, does not threaten India’s recently awarded polio free status because though detecting VDPV is part of the surveillance system, it does not get added when putting together a country’s polio numbers.
Only infections caused by wild polio virus strains like P1 and P3 get counted. The infected child is from Lalbagh block of Murshidabad district. Detailed follow-up investigations are being carried out. Preliminary reports indicate that the child was admitted to a hospital recently and has been ill for prolonged periods indicating the possibility of immunodeficiency.
Oral polio vaccines (OPV) contain a weakened version of poliovirus, activating an immune response in the body. A vaccinated person transmits the weakened virus to others, who also develop antibodies to polio, ultimately stopping transmission of poliovirus in a community. According to experts, in very rare instances, the virus in the vaccine can mutate into a form that can paralyze — this is what is known as a VDPV.
In 2011, India reported seven cases of VDPVs — one of them in a child with congenital immune deficiency in Dhamtari district in Chhattisgarh — and the others in areas with low routine immunization coverage like Udaipur (Rajasthan), Ghaziabad and Badaun (Uttar Pradesh), Barnala (Punjab), Vidisha (Madhya Pradesh) and Jajpur (Orissa).
None of the VDPVs detected in India during the past two years have shown evidence of circulation. None of the VDPV strains detected in India during 2010 and 2011 are genetically linked to each other. In response to the VDPV cases, state and district authorities, through the National Polio Surveillance Programme, have conducted catch up routine vaccination and localized polio vaccination campaigns.
Health ministry officials say importation of wild poliovirus remains the greatest threat to children in India.
Experts say OPV is a very safe and effective vaccine that has protected millions of children from paralysis. It was the bivalent polio vaccine that brought down India’s polio cases to zero.
According to WHO, from 2000 to 2010, more than 10 billion doses of OPV were administered to over 2.5 billion children. As a result, more than 3.5 million polio cases were prevented. During that time, 18 outbreaks of circulating VDPVs occurred in 16 countries, resulting in 510 VDPV cases.
The small risk of VDPVs pales in significance to the tremendous public health benefits associated with OPV. Every year, hundreds of thousands of cases due to wild polio virus are prevented. Well over eight million cases have been averted since largescale administration of OPV began 20 years ago.
Circulating VDPVs in the past have been rapidly stopped with 2-3 rounds of high-quality immunization campaigns. The solution is the same for all polio outbreaks: immunize every child several times with the oral vaccine to stop polio transmission, regardless of the origin of the virus.
India’s achievement in stopping wild polio virus transmission is being considered one of the greatest achievements in public health in the 21st century.
Prime Minister Dr Manohan Singh said the real credit for this major achievement goes to the 23 lakh volunteers who repeatedly vaccinated children “even in the most remote areas, often in very bad weather conditions”.
India recorded 741 cases of polio in 2009 – nearly half the number of global cases. But in a remarkable turn of events, India reported just one case of the crippling disease in 2011 and went on to record zero cases in over 12 months since then.
The debate on whether Inactivated Polio Vaccine (IPV) – produced from wild-type poliovirus strains of each serotype that have been inactivated (killed) with formalin and given as an injection – will required to be given to complete the eradication process (as only then will VAPP and VDPV infection be eliminated) is ongoing. As many as 10 outbreaks of VDPV in 9 countries affecting 209 cases have been recognized in the last decade. India at present is at a low risk for a VDPV outbreak due to high immunization coverage. However, decline in immunization coverage (esp of routine trivalent OPV), eradication of wild polio virus, high force of transmission and monovalent OPV use could create a setting favourable for a VDPV (most likely of type 2 polio virus) outbreak. And this is the reason why some experts feel that continuing to vaccinate against polio with IPV, after stopping OPV, is mandatory in the post-polio eradication scenario. The evidence against employing this very costly and difficult-to-implement intervention is the fact that most countries have eradicated polio using OPV alone.
<”><”><”><”><”><”>Dr Jeeson C Unni MD, DCH, FIAP
Editor-in-chief, IAP Drug Formulary
Consultant pediatrician, Dr Kunhalu’s Nursing Home, Cochin