The Indian government reported just 42 cases last year - down 94 per cent from the year before, and the lowest number ever recorded here.
That news is, in a way, even better than it sounds: In the entire high-transmission season, which comes with the summer monsoon, there was not a single case in Uttar Pradesh, and just three in Bihar. From nine distinct genetic clusters of Type 1 polio virus in 2006, there is now just one.
"We've never been this close," Dr. Jafari said, his voice lowered, as if not to tempt fate. "We've never seen this picture before."
That said, the fight is not over in India: there was an unexpected, fast-moving outbreak in West Bengal last year caused by a virus from Bihar. But an extensive "mop-up operation" is under way there now, before the rains come, and if no new cases are reported for 18 months, India will be removed from the list of four countries where polio remains endemic.
One of the holdouts is Nigeria, which had a sharp flare-up in cases after 2003. In Nigeria, state governments banned vaccination when rumours spread that the polio vaccine was actually being used to sterilize Muslims. The virus spread from Nigeria back into 12 countries that had wiped it out. Heavy lobbying persuaded Islamic leaders to urge people to co-operate with vaccinators. Nigeria reported just 21 cases in 2010, down from 388 cases in 2009. Experts believe eradication may be possible there soon.
The last two endemic countries are Afghanistan and Pakistan. Despite the weak state and vicious fighting in much of Afghanistan, a team there has successfully negotiated with warring factions to allow access to children.
India will need to maintain the rounds of mass vaccination for a few years, to keep herd immunity high - and also redouble efforts at surveillance, so that if a new case pops up, it is caught immediately.
The surveillance network investigates all reported cases of acute flaccid paralysis, the tell-tale sign of polio - some 55,000 a year.
The WHO team regularly reminds doctors in hospitals and private practice to call their hotline the moment they see a limp-limbed child. It also cultivates relationships with herbalists, village healers and temple priests, to whom poor people often take sick children first.
The cause is not without dedicated backers: Mohammed bin Zayed Al-Nahyan, the crown prince of Abu Dhabi, recently pledged $50-million to vaccinate children in Pakistan and Afghanistan, while the Gates Foundation has pledged another $450-million for the next two years.
But, Dr. Aylward said, it isn't enough: they need the world's richest nations to pitch in further. In 2005 (and many times since), the G8 member countries pledged to maintain or increase their contributions, yet G8 contributions for 2011-12 account for just 12 per cent of the global campaign's $1.86-billion budget, compared with 58 per cent in 2004-05.
Walter Orenstein, a polio expert with the Gates Foundation, called this the greatest threat: that in an era of economic downturn, donors will think that almost eradicating polio sounds good enough. "We will get periods of silence," he warned. "And then outbreaks like in Congo or Tajikistan."
The budget shortfall means that Dr. Aylward is "cutting corners" in vaccine rounds in Nigeria, scaling back a vaccination campaign in Congo and restricting surveillance in India. It's risky. And if the disease isn't wiped out, he said, when the world came this close, it will stand as a stark rebuttal to the idea that all children are created equal. "If we don't end polio now, we're not saying it's because we can't, we're saying, 'It ain't worth it.' Because now, we have no excuse. Now we know it's doable."