Just a few years ago, skepticism ran deep about the chances that India would ever be able to stop polio from paralyzing its children.

While in recent years most cases occurred in or emanated from two northern states -- Uttar Pradesh and Bihar -- polio routinely crippled somewhere between 550 and 900 Indian children a year. And polioviruses from India regularly found their way to far-flung places, triggering outbreaks in nine countries over two continents since 2005 alone.

But then, something shifted. Between 2009 and 2010, the balance tipped. Today, India is on the verge of being declared polio-free.

Some might be tempted to call it a miracle. But they would be ill-advised to use that word around anyone who has sweated and strained and fretted and strategized to get the country to this point.

Dr. Bruce Aylward, the affable Canadian who serves as the World Health Organization's assistant director general for polio, veritably growls at the suggestion. "It's not a miracle -- it's good science and an awful lot of elbow grease."

Millions of volunteers, more than 150,000 supervisors and US$2 billion in funding from the government of India alone have gone into the mammoth effort to get India where it is today. Proud. Nervous. And poised to enter the next phase of its long battle against polio.

"We are very excited," says Anuradha Gupta, joint secretary in India's ministry of health and family welfare, and the country's point person for the polio effort.

"We think this progress is great, very heartening. But I think we are also mindful of the risks that still persist," she says in an interview from New Delhi. "This is not the end of the road."

Gupta is right. But it is definitely a welcome milestone along the way.

The last Indian child paralyzed by polio became ill on Jan. 13, 2010. It's been well over a year since poliovirus has been found in sewage samples -- one of the forms of polio surveillance India uses -- that are collected weekly in three key Indian cities.

If the country produces 12 straight months of polio-free surveillance data, the Global Polio Eradication Initiative will drop India from the list of polio-endemic countries. That term is used to differentiate the countries that have never managed to stop spread of polioviruses within their borders from those that have. Currently only Pakistan, Afghanistan, India and Nigeria remain on the endemic countries list.

While the partners in the polio eradication effort -- the WHO, UNICEF, Rotary International, the U.S. Centers for Disease Control and the Bill and Melinda Gates Foundation -- are issuing congratulatory statements this week on the one-year anniversary, it will actually be sometime next month before official word comes.

That's because sewage samples and tests from children being investigated as possible polio cases take awhile to work their way through India's busy polio laboratory. Processing of all tests taken within the 12-month period should be completed sometime in February, the WHO estimates.

If India clears the one-year mark, it will put the 11 countries of SEARO, the WHO's Southeast Asian subgroup, on track to be declared polio-free.

That will only happen if all the countries see no evidence of spread of indigenous polioviruses for three years running. (The 12 months count as the first year.) Successfully battled importations don't stop that clock.

But they do pose a real threat now to India, which until recently was a major source of renewed spread to parts of the world which had previously gotten rid of their own polio problems. Polio is still paralyzing children in the three other endemic countries, and in about a dozen other countries that have seen transmission re-established due to imported viruses.

Dr. D.A. Henderson, of the Center for Biosecurity at University of Pittsburgh Medical Center, thinks India should be able to hold on to its polio-free status once it achieves that goal. Henderson, who led the global campaign to eradicate smallpox, says there isn't a substantial amount of travel between India and the countries still fighting polio.

But in India, no one is taking anything for granted. Gupta explains that all states have emergency response plans that will kick into action if polioviruses from outside make their way to India.

"Our biggest enemy at this time would be complacency and to think the job is done -- because the threat of importation is real," agrees Dr. Hamid Jafari, project manager for the World Health Organization's National Polio Surveillance Project.

How did India achieve what seemed unachievable for so long? Better targeted vaccines made a definite dent in the problem, observers say. But much of the credit goes to ongoing improvements to the planning and organization of the country's polio strategy, many say.

"India's success is really the result of visionary determination and dogged persistence," says Sir Liam Donaldson, former head of Britain's Health Protection Agency and chair of an independent panel that critiques the global polio campaign for the WHO.

A major part of the success is due to the country's recognition that poor migrant families were being missed by polio vaccinators and were moving the virus around with them. At any point in time millions of Indians are on the move looking for work, a surging wave of internal migration.

Coming up with a way to find and track those missing children was a strategy that was "unique and special and was necessary," says Dr. John Sever, vice-chair of Rotary International's PolioPlus program, which by the end of next year will have raised nearly US$1.2 billion for polio eradication.

Polio workers mapped where families set up temporary camps around brick kilns in Uttar Pradesh. They set up vaccination distribution centres at transit points -- train stations, bus depots, intersections of highways that teem with buses, cars, auto-rickshaws and motorcycles that carry whole families.

Jafari says they now manage to vaccinate about 4.1 million migrant children. All told, a national polio immunization day sees roughly 2.3 million vaccinators hit the road to visit 209 million households.

"It's been a very long struggle. Every weapon we could muster was thrown into the battle," says Dr. T. Jacob John, one of India's leading polio experts and a professor at Christian Medical College in Vellore, in the southern Indian province of Tamil Nadu.

John admits his emotional reaction is more one of "relief than excitement."

What next? Well, the global polio program's latest deadline to stop the spread of polio is by the end of 2012. Henderson rates the chances of that happening at between 20 and 25 per cent. And Donaldson's monitoring group estimates only India will hit the mark, unless major changes are made.

Sever is hoping the psychological boost of a big victory after years of heartbreaking setbacks will spur progress elsewhere. "It shows that with sustained effort and with a well organized program, it is successful in India and similar programs with different needs should be successful in the remaining countries too."