Vaccination could eradicate India's persistent polio problem, health experts say.
Mass child immunisation is key
Despite massive immunisation efforts, almost a third of all polio cases in the world occur in India.
UK experts at Imperial College London say they have identified the main factors that let the virus rage here - poor sanitation and overcrowding.
They told Science magazine a newer polio vaccine should be able to overcome these obstacles.
Two months ago, India's health minister held an emergency meeting of officials from the states affected by the disease.
Last year, only 66 cases of polio were recorded in India, but there have been 522 cases so far this year.
In the impoverished states of Uttar Pradesh and Bihar, where India's recent polio epidemics originate, poor sanitation and high population density are the key obstacles to eradicating the virus, says lead researcher Dr Nicholas Grassly.
Both these conditions make it easier for the virus to spread and make the polio vaccine less likely to work.
Water or food contaminated by the faeces of infected people could pass the virus on to others, Dr Grassly explained. Overcrowding increases the risk the virus will spread and high birth rates makes it difficult to immunise new babies against polio in time.
Until 2005, the vaccine used was designed to fight three strains of virus that cause polio.
But individuals needed more doses of the vaccine to offer effective protection against the different strains.
Some people did not receive enough doses, meaning polio could continue to thrive.
The type 1 strain of the polio virus is now the dominant strain in India.
The researchers believe that using a vaccine that targets only this strain of polio - a monovalent vaccine - could be the way to eradicate polio.
Oliver Rosenbauer of the Global Polio Eradication Initiative at the World Health Organization (WHO) agreed: "By using now a monovalent polio vaccine which offers protection against type 1 polio you would get much better protection much faster for fewer doses than with the traditional trivalent vaccine.
"The catch is it only works if you vaccinate children. The key still is reaching enough children."
He said this was a big challenge. "Every month in the Uttar Pradesh state, 250,000 children are born who all need vaccinating.
"It is achievable if you can reach a sufficient number of children. For global success, we need to finish the job quickly."
The disease, which attacks children under five years, affects the nervous system and can result in paralysis.
Although polio has no cure, it is easily preventable through vaccine.
Before 1988, when WHO launched a global anti-polio campaign, there were more than 350,000 cases worldwide.
Today, the disease has been eradicated in much of the world but is still found in some countries, including India, Nigeria, Pakistan and Afghanistan.