Nigeria has asked international donor agencies to check a polio vaccine after three of its northern states halted an immunisation drive over safety fears.
Most parts of Nigeria have embraced the vaccine programme
The states acted after an influential Islamic leader said the vaccines might cause cancer, Aids or sterility.
Nigerian Vice-President Atiku Abubakar said the analysis was necessary to remove all doubts about the vaccines.
But the World Health Organisation insists that the vaccines were tested and are entirely safe.
Mr Atiku told a meeting of international donors that there should be a meeting to "find a solution to the various issues surrounding the analysis of the polio vaccines".
The head of the WHO's polio campaign, David Heymann, has told the BBC that the vaccines used in Nigeria are no different from those used to combat polio everywhere else in the world.
Mr Heymann said the vaccines had been undergoing testing by local scientists in several Nigerian states since August and said he did not understand why the results had not been forthcoming.
He said the immunisation programme had not been disrupted in neighbouring states by fears over the quality of the vaccine.
The WHO campaign was launched last week in a bid to immunise more than 15 million children in west and central Africa against polio.
Nigeria has the world's highest number of cases and, the UN says, the virus now threatens areas that were previously polio-free both in Nigeria and across the region.
With the take-up of vaccines so low in northern Nigeria, polio was taking firm hold, Mr Heymann warned.
This Nigerian child is now protected
Three predominantly Muslim states in northern Nigeria - Kano, Kaduna and Zamfara - objected to the campaign amid rumours that the vaccines were contaminated.
Datti Ahmed, who is both a medical doctor and the president of Nigeria's Supreme Council for Sharia law, said they the reports had to be checked out.
The latest crisis threatens to undermine a global initiative to eradicate the crippling disease by the end of 2004.
Poliomyelitis is an acute viral infection which mainly affects children and can be spread by simple physical contact.
It causes permanent paralysis and other forms of physical disability in many of its victims.