On January 13, 2011, an 18-month-old infant in Howrah district of West Bengal was found to have been crippled by a naturally occurring wild strain of the polio-causing virus. However, no more children fell victim to such viruses over the next one year and India was then removed from the list of countries where polio is endemic. India has remained free of polio, and analysis of sewage samples have not turned up any signs of the virus lurking silently in the environment. Once final tests confirm that the wild virus has not been seen here for the last three years, the World Health Organisation’s 11-nation South-East Asia Region (of which India is a part) can be formally certified as polio-free. This region will then join the three that already enjoy this status — the Americas, Western Pacific and Europe. For India, this is an enormous public health achievement. Not so long ago experts believed that India, with its huge population, many poor and living in squalor, would be the very last to eradicate polio, a disease that once struck 50,000 to 100,000 Indian children annually. Even in 2009, nearly half of the world’s polio cases were occurring here. Yet, through determined efforts and systems to ensure that no child was missed during immunisation drives, transmission of the wild virus has been halted. Each national immunisation campaign is a mammoth operation, with 2.4 million vaccinators reaching oral vaccine drops to some 170 million children.

But the job is not over yet. Although no child in India has been paralysed by wild polio viruses over the last three years, several have been affected during the period when live but weakened strains of the virus used in the oral polio vaccine turned virulent again. Such vaccine-derived viruses can also spread like wild ones and be just as dangerous. In order to safely withdraw oral vaccines, all countries that rely on them have been asked to introduce at least one dose of an injectable polio vaccine based on killed viruses into their routine childhood immunisation. In India, steps are being taken to strengthen the way such immunisation is provided, particularly in States where vaccination levels are low, by incorporating lessons from the polio campaign for reaching every child and gaining community acceptance. Moreover, polio is still endemic in Pakistan, Afghanistan and Nigeria, and in the past year the viruses have spread from there to other countries. There is therefore the risk that the virus might be imported into India too. As long as it continues to circulate in the world, India and other countries that are polio-free must keep their guard up.