By Fergus Walsh
BBC medical correspondent
World health officials say they are moving closer to the global eradication of polio.
Nigeria has two thirds of the world's cases of polio
The disease paralyses the lower limbs. It is caused by a virus which is shed in faeces and transmitted through poor sanitation and contaminated water.
The main stronghold of polio is northern Nigeria, which has two thirds of the world's cases each year.
If the disease is ever to be defeated then Nigeria is the key.
If polio is halted in Nigeria it would be a remarkable turnaround.
Two years ago polio immunisation was halted in the northern state of Kano and the surrounding area.
A scare story emerged suggesting that the oral polio vaccine was contaminated with oestrogen and could cause infertility.
The regional government set up a committee to investigate the claims, which cleared the vaccine.
Unfortunately, the virus was able to thrive during the 12-month boycott.
Polio cases doubled in Nigeria in 2004 and the disease re-infected 16 previously polio-free countries, as far afield as Indonesia.
In each case the virus can be traced back to Nigeria.
But polio immunisation is now back on track in the African country.
A BBC team followed the army of vaccinators as they spread out across Nigeria with the aim of immunising every child under the age of five in just four days.
No-one knows exactly how many eligible children there are but the teams carry with them 43 million doses of oral polio vaccine.
The teams knock on every door in every street in every town and village.
Each child is given two drops of the vaccine and then their little finger is marked with indelible ink.
The child's house is marked with a chalk circle and the vaccinators move on.
Each child needs three to four doses to be fully protected so the whole process is repeated several times each year.
It is too late though for Umar Ahmed.
POLIO IN NIGERIA
2003: 355 cases
2004: 792 cases
As of 1 June 2005: 131 cases
The little boy was born at the end of 2003 during the polio boycott.
As a result he was not immunised and he caught polio.
He should be toddling around now - but he will never walk.
His father and mother both have polio and wanted him protected.
They both know how difficult life is in Nigeria for those with disabilities.
Umar's father Aminu held his son up and said: "Look at the leg.
"See this one is not working. He will never walk.
"That's why I tell people to drink this vaccine because I don't want to see another small boy get polio".
Aminu is chairman of the Polio Victims Association of Kano.
Para Soccer players are not allowed to kick the ball
Every week the group turns out dozens of hand-operated tricycles.
The brightly-painted machines are visible over the city.
Aminu says they are important for children as it means they are not trapped by their disease and can go to school.
He will have a bike ready for his son when the time comes.
As well as adapting bikes, polio victims here have also adapted the rules of football to create their own version of the game.
Para Soccer is played at breakneck speed with the players sitting on small skateboards.
They hit the ball with their hands - kicking it is not allowed.
Usman Yusef said he got polio when he was six-years-old.
Before that he could walk and run. Now he uses crutches or the special tricycle.
"I play soccer... to keep fit and to get rid of the anger I feel at being disabled," he said.
He asked whether there is a polio soccer team in the UK and was amazed to hear that the disease has been eradicated from Europe.
The official target is to stop transmission of polio in Africa by the end of this year.
Health officials know that is unrealistic and hope instead they will achieve this by the end of 2006.
Nigeria's representative from the World Health Organization said Africa has "so many other health challenges", like HIV/Aids, malaria and tuberculosis.
"The sooner we can get rid of polio, the more resources will be invested on these diseases," Mohammed Belhocine said.
Ridding the world of polio would be an incredible achievement.
The Global Polio Eradication Initiative began in 1988 when 125 countries had the disease and there were 350,000 cases every year.
The disease is now endemic in six countries and last year there were 1,266 cases.
The disease will be deemed to be eradicated once the world is free of polio for three years.
The only other time that happened was a quarter of century ago with smallpox.