Bill Gates: The world can defeat polio
Glance at the latest figures for polio incidence and it would appear that the world is within touching distance of eradicating the disease.
Last year there were just 205 cases of naturally occurring poliovirus compared with 650 cases in 2011 and a staggering 350,000 a quarter of a century ago.
There are now three countries - Pakistan, Afghanistan and Nigeria - where transmission of the disease has never been halted compared to 125 countries in the late 1980s.
India has been polio-free for two years - a remarkable achievement.
This week the billionaire philanthropist Bill Gates will deliver the annual BBC Richard Dimbleby Lecture in which he will spell out his commitment to ridding the world of this dread infectious disease which can cause paralysis and even death within hours.
Bill Gates is the single most influential voice in global health, so when he turns his attention to an issue, it is worth listening.
Through the Gates Foundation, Bill and his wife Melinda have already given away nearly $30 billion of their fortune and there are tens of billions more in the pipeline.
He has spoken to me previously of his passionate belief in the power of vaccines and his determination to defeat polio.
In his lecture Mr Gates will liken the pace of innovation in computers with the fight against polio: .
He will say: "In the late 1970s we had a dream of giving everybody access to computer technology - a vision of a computer on every desktop. Now there is a computer in every pocket.
"The pace of innovation keeps getting faster. The same is true of polio.
"It was first recognised at least 4,000 years ago, but it was just 200 years ago we figured out it's contagious - just 100 years ago we learned it's a virus. Just 50 years ago we developed the vaccine to prevent it.
"Just 25 years ago we resolved to eradicate it. And so on."
But Mr Gates will also acknowledge that the final push against polio is proving extremely difficult: "I can say without reservation that the last mile is not only the hardest mile; it's also much harder than I expected," he said.
The killing of nine health workers in Pakistan last month was a shocking reminder of the challenges facing those trying to chase down the virus and protect every last child. I have written before of the hurdles facing immunisation teams.
Part of polio's danger is its utter portability - it can be spread across borders by one infected traveller, who can continue to shed virus for weeks on end.
Only last week an emergency vaccination programme was ordered in Cairo after samples of the polio virus were found in sewage - the strain matches that in southern Pakistan.
The oral polio vaccine can - in very rare cases - trigger polio. The WHO says this happens in one in 2.5 million first doses of vaccine.
Over the past decade 15 billion doses of polio vaccine drops have been given and there have been 200 confirmed cases of circulating vaccine-derived polio virus.
But with naturally occurring polio cases now so low there is a minority which claims the oral live vaccine is causing significant harm.
Dr Jacob Puliyel, a paediatrician in Delhi, wrote in the Indian Journal of Medical Ethics last year that "the polio eradication programme epitomises nearly everything that is wrong with donor-funded 'disease specific' vertical projects, at the cost of investments in community-oriented primary care".
Dr Puliyel said the money spent on fighting polio in India would have been put to better use on water, sanitation and routine immunisation.
Now or never
Dr Puliyel blames the polio vaccine for a sharp rise in India of cases of Acute Flaccid Paralysis - weakness or inability to move limbs.
But polio is just one of many causes, with other viruses and bacteria also responsible. Public health officials also point out that monitoring of cases is now far better than in previous decades.
In pure economic terms it is hard to justify the $1bn (£630m) spent annually on driving down polio cases by a few hundred each year.
It makes sense only if global eradication is achieved. Then the repeated - sometimes monthly - polio immunisation rounds in at-risk communities can stop and the vaccine be part of the standard childhood schedule.
This is a now or never moment - kick polio off the planet over the next few years or face a humiliating retreat which could see the virus re-emerge in scores of countries.
Bill Gates recognises what is at stake for global health: "Polio eradication is a proving ground, a test. It will reveal what human beings are capable of, and suggest how ambitious we can be about our future."
The 2013 Richard Dimbleby Lecture will be shown on Tuesday 29 January on BBC One at 22:35 GMT