Fifteen million children in five west and central African states are being immunised against polio in an emergency three-day blitz aimed at preventing the crippling disease regaining a hold in those countries.
Hundreds of thousands of health workers and volunteers yesterday began administering oral vaccine in an attempt to turn back the disease, which has spread from Nigeria, where it is still endemic.
The crisis threatens to undermine the goal of eradicating polio throughout the globe, and has prompted a remarkable grassroots effort to reach families whose homelands border or are in the danger zone. The political uncertainty surrounding elections in Nigeria this year has helped to undermine the country's immunisation programmes.
About a dozen cases of children paralysed by polio of a type linked to northern Nigeria by genetic tests have recently been found in Burkina Faso, Ghana, Niger and Togo.
Children in these four countries, plus Benin, are regarded as being at risk of contracting the disease.
The global eradication initiative is spearheaded by the World Health Organisation and is supported by private foundations, donor governments, humanitarian organisations and companies.
The blitz, organised at a cost of more than $10m (£5.9m), will mean more financial problems for the initiative, which is already short of the $210m it says is still needed to help wipe out the disease by 2005. Population movements, including nomadic journeys and family and business trips, are likely to have helped to spread the disease, although tracking its exact path would be almost impossible.
Chad, where a case has also been identified, and Cameroon will become extra targets for immunisation programmes next month.
Polio-infected states around Kano in northern Nigeria have reinfected other areas within the country, most worryingly Lagos, with 10m inhabitants.
The southern part of Nigeria had been free for two years.
David Heymann, the WHO's senior official in the fight against polio, said: "Nigeria is now the country with the greatest number of polio cases in the world. Polio continues to spread within Nigeria. We face a grave public health threat, and our goal of a polio-free world is under threat."
The African outbreak represents the biggest challenge yet to a change of policy introduced in May, when the global initiative, which had previously funded campaigns in scores of countries freed from the disease, decided to target resources on the last seven endemic strongholds for polio - Nigeria, India, Pakistan, Egypt, Afghanistan, Niger and Somalia.
The initiative also focused on six countries regarded as in danger of relapse - Angola, Bangladesh, Democratic Republic of Congo, Ethiopia, Nepal and Sudan.
More than $2bn has been spent on the initiative in the past two decades and polio cases recorded worldwide have fallen from the 350,000 cases a year of 1988. In the year to October 14, there were just 414 cases, 178 in Nigeria.
Bruce Aylward, the global coordinator for the initiative at the WHO, said: "Because of the tremendous progress made in 2002 , polio eradication tactics and resources were switched in 2003 to focus on those few remaining countries which remained endemic.
"But the situation in Nigeria is now forcing us to go back to countries which had already eliminated polio. We simply cannot allow these isolated viruses again paralysing children in areas which had been polio-free. This is why this massive campaign is critical."
Nigeria has promised to step up programmes to ensure that polio is eradicated there by the end of next year.
