As polio cases surge in Nigeria and the virus spreads to other countries, western and central Africa are on the brink of the largest polio epidemic in recent years, officials of the World Health Organization and Unicef said Tuesday.

The 60 polio cases reported by Nigeria last week are the largest number for any week in recent years, the officials said.

Last weekend, genetic testing of a child who became paralyzed on May 20 confirmed that a 10th country, Sudan, had experienced polio exported from Nigeria. The health agency called that finding “a stark warning.”

Equally alarming, health officials said, is that the surge in polio cases in Nigeria and its spread to other countries is occurring during a season when transmission of the polio virus is usually at its lowest. That signals the potential for a large epidemic as polio enters the season when transmission is highest, they said.

“It’s a totally unnecessary public health tragedy,” Kul Gautam, deputy executive director of Unicef, told reporters in a telephone news conference.

Further, the threatened epidemic comes while the World Health Organization and its partners expected that a $3.1 billion program begun in 1988 was about to make polio the second disease to be eradicated from the world, after smallpox.

Instead, Dr. Bruce Aylward, a WHO polio official, said in a telephone news conference that “we could see thousands paralyzed at a time when the disease should be eradicated.”

Despite what they acknowledged was a serious setback, officials of the United Nations agencies and a major partner, Rotary International, maintained their optimism, saying that they could salvage their goal of eradicating the disease by the end of the year.

But to do so, they said, would require an additional $100 million to immunize 74 million children in 22 African countries in a synchronized program in October and November. These countries would cover the area extending from Mauritania in the north to the Congo in the south, and from Senegal in the west to Sudan in the east.

A program that immunized at least 90 percent of the children in vulnerable areas could stop transmission and still allow the WHO to meet its goal, Gautam asserted.

One reason for maintaining optimism, Aylward said, was that large immunization programs had quickly controlled two major epidemics in 1999. One involved 1,103 cases in Angola; the other 500 cases in the Congo.

A key to success is the willingness of the Kano state in northern Nigeria to quickly resume polio immunizations, which were stopped last August because political and religious leaders claimed that the vaccine made girls infertile.

Tests of the vaccine have refuted such claims, said Dr. David Heymann, director of the World Health Organization’s polio eradication program. The vaccine as purchased by Unicef meets the health organization’s standards and has been used safely to eliminate the disease from many other countries.

In May, the Kano state governor, Ibrahim Shekarau, pledged to resume vaccinations. But that has not happened, Heymann said.

Also, allegations about the impurities and safety of the polio vaccine have caused alarm and confusion among many people in Nigeria and elsewhere.

The World Health Organization is considering other measures, including a travel advisory, Heymann said. But the effectiveness of such an advisory is uncertain because the spread of most polio cases to other countries is believed to have resulted by people traveling across porous borders, not from air travel.

The New York Times