Even as the news swells with many issues of social justice, including the arrest of vocal student leaders and activists of adivasi rights, and basic science had its brief moment of fame when scientists heard the sound of gravitational waves, something that the nation can be proud of has been pushed to the background. India has been polio-free for five years now – the last case having been reported on January 13, 2011 in Howrah, West Bengal – and the ‘Pulse Polio’ campaign in its present form is being wound down.
Polio is an old disease. Imagery strikingly similar to cases of polio have been seen in 3,000-year-old Egyptian paintings. Michael Underwood, a doctor from London, in his Treatise on The Diseases of Children (1799), described a polio-like disease as a weakness of the lower extremities in the late 18th century. He wrote, “The first thing observed is a debility of the lower extremities, which gradually become more infirm, and after a few weeks are unable to support the body (sic), there being no signs of worms, nor other foulness…” The first major outbreaks in Europe and the US were reported in the 19th century.
The disease, which then used to cause over 20,000 paralytic attacks every year in the US, could be contained rather rapidly with the introduction of the first polio vaccine in 1955, developed by Jonas Salk. By the late 1970s, the country was polio-free.
The Salk vaccine was an inactivated polio virus, which when injected into a human would mount an immune response and so provide individual protection against wild polio. This vaccine had to be injected and is part of the regular immunisation that we give our kids through their paediatricians. This is a highly successful vaccine and is being used worldwide.
The live attenuated form of the vaccine, given orally, was developed by Albert Sabin in 1961. This is essentially a live polio virus but carrying mutations that make it non-virulent. This came with some advantages. The oral mode of delivery is obviously more convenient. And because it is consumed through the gastrointestinal tract, it provides mucosal immunity in this part of the body. Wild poliovirus is also contracted through the tract and therefore immunity given by the OPV could prevent infection of the gut by the wild virus.
Importantly, the live attenuated virus, like the wild disease-causing virus, is shed through the stool, finding its way into the soil and water – the usual routes of spreading the wild virus. This means that anyone who happens to eat food that had come in contact with these environmental sources would also get the benefit of immunisation. Even a child who has taken the inactivated vaccine could get immunised with the OPV, and make her first contribution to the nation’s and the world’s health!
The OPV comes with the disadvantage of containing a live virus. The virus could revert the inactivating mutation and cause polio in the vaccinated individual. However, the chance of this is very low – and a lot lower in children with reasonable immune systems as well as among those who had already taken an earlier dose of the vaccine – that the benefits to the individual and the community outweighed the disadvantages. However, in developed countries such as the US, OPV was discontinued in 2000 as the risk of vaccine-attributable disease was much less (essentially zero) with the injected variety.
As late as 1988, there were 350,000 polio cases worldwide. In that year, India had 150,000 polio cases. This despite the proven success of the vaccine and the elimination of the disease from the US and the promise of worldwide polio eradication that the vaccine offered.
India started the ‘Pulse Polio’ campaign way back in the mid-1990s, taking advantage of the ease of use and the community protection offered by the OPV. The logistics and the numbers are staggering. Over 2 million vaccinators, regulated by some 150,000 supervisors, immunise 170 million children under five twice every year. Every neighbourhood landmark and – these days – large apartment complexes see these heroic volunteers giving polio drops. Many medics ensure coverage by door-to-door vaccination for a few days following the big ‘Polio Sunday’ (#poliosunday). And we do claim 100% coverage. This is a herculean achievement given the socio-economic background of much of our citizenry. From thousands of recorded cases of paralytic polio every year in the mid-1990s to double digits in 2010 to zero since January 2011, we have come a long way.
India is currently giving its last doses of OPV to children under five. We can always debate whether polio is or was our greatest challenge in countering infectious diseases. But the moral of the story is that the Indian system can crank up, flex its muscles and get things done against all odds if it really wants to. We celebrate the success of the Great Indian Elections and universal suffrage; let us celebrate the success of ‘Pulse Polio’, and celebrate the fact that we were part of it. So long, polio!
Aswin Sai Narain Seshasayee runs a laboratory researching bacterial biology at the National Centre for Biological Sciences, Bengaluru. Beyond science, his interests are in classical art music and history.