Under the plan nearing approval, scientists would be able to add a gene to the smallpox virus to make it faster and safer to determine whether drugs developed since the disease was eradicated in 1977 will work well.

The plan calls for adding to the virus an inactive green protein that would function as a marker gene, glowing green under a fluorescent light if the smallpox virus was still alive. It would not affect the potency of the virus.

"The principle of using this testing has been accepted, but the WHO noted that countries are particularly concerned about biosafety and biosecurity -- about ensuring absolute safety in working with this virus," said WHO spokeswoman Christine McNab.

The full assembly is expected to accept the decision Monday, health officials said.

But the committee sent back for further study a proposal to allow possibly riskier genetic manipulation of the smallpox virus.

Under the plan nearing approval, scientists would be able to add a gene to the smallpox virus to make it faster and safer to determine whether drugs developed since the disease was eradicated in 1977 will work well.

A key committee of the assembly, which supervises the World Health Organization, has noted plans that would include adding a green marker protein to the smallpox virus.