The last case of the crippling disease was detected on January 13, 2011 in a two-year-old girl in India's West Bengal state. A full year without any new cases will mean India will no longer be "polio-endemic," leaving only Afghanistan, Pakistan and Nigeria.

"We are all subject to relaxing a bit when we have achieved some goal but we simply cannot allow that to happen with polio," Nata Menabde, the India head of the World Health Organization (WHO), told AlertNet in an interview.

"The important point is that while India may have stopped transmission of wild polio virus, it does not prevent such a virus from being re-imported or in fact the virus could be around and it has just not been detected."

Menabde said that while one year of no reported cases of the virus was an important public health achievement, it would take another two years of no cases before India could be certified as being "polio-free."

Until the 1950s, the disease crippled thousands every year in rich nations. It attacks the nervous system and can cause irreversible paralysis within hours of infection.

It often spreads in areas with poor sanitation -- a factor that helped it keep a grip on India for many decades -- and children under five are the most vulnerable. But it can be stopped with comprehensive, population-wide vaccination.

Just two years ago, 741 Indians fell sick with polio, nearly half the world's cases that year. The number of reported cases dropped to 42 in 2010 and only one last year.

Menabde said the secret of India's success was based on several factors, including a mass eradication program costing billions of dollars and mobilizing millions of people across the country to give every child under five the oral polio vaccine.

Around 900,000 doses of oral polio vaccine were given, immunizing 172 million children and involving 2.3 million vaccinators who visited 200 million homes in 2011 alone.

India has also used mobile vaccination teams that immunize children at bus stops, train stations, inside moving trains and in marketplaces.

But the health official took a cautionary note, saying that these efforts needed to continue as there were countries such as Tajikistan, Angola, Bangladesh and Russia which were certified as polio-free for many years, but had seen re-infections.

"If even one case occurs here again, we really have to mobilize a major effort and respond to it as emergency and do the mop up campaigns and vaccinate children around the area where such a thing may happen," said Menabde.

"It has been a major investment, we have to sustain this success, we have to finish the job as while there is one polio case in anywhere in the world, every country is vulnerable."

• A Permanent Economic Emergency