Chicago --- The worldwide eradication of polio is unachievable and efforts should be abandoned, a senior federal health official said Saturday.

Dr. D.A. Henderson, who led the global campaign to eradicate smallpox 20 years ago and is now the government's most highly placed bioterrorism expert, roiled a scientific meeting here by proposing that the labor-intensive $2 billion effort against polio be rolled back and routine immunization resumed indefinitely.

"There is something we should eradicate, and that is the word 'eradication,' " said Henderson, who spoke to the Infectious Diseases Society of America on the 25th anniversary of the last case of smallpox, the only disease ever successfully eradicated.

The polio effort is headed by the World Health Organization but is organized and substantially funded by the Atlanta-based Centers for Disease Control and Prevention, which reacted swiftly and negatively to Henderson's proposal.

"To stop now would be snatching defeat from the jaws of victory," said CDC immunization expert Dr. Stephen Cochi, who challenged Henderson from the floor at the meeting.

"We certainly don't think the goal should be abandoned," said Dr. Walt Orenstein, director of the CDC's national immunization program and chairman of a WHO polio advisory group. "Tremendous progress has been attained."

Polio is a crippling, sometimes fatal disease that largely affects children. The virus, which attacks nerves that control movement, lives in the gut and is spread by contact with fecal material. The last case in the United States occurred in 1979.

Setbacks abound

When the worldwide campaign was launched in 1988, polio was still circulating freely in 125 countries. At the end of 2001, that had been reduced to 10 countries in the developing world. The CDC hopes to announce in December that the virus has been confined to five countries, with most of the remaining cases in India, Pakistan and Nigeria.

WHO's original goal was to record the last case of polio before the end of 2000, monitor the situation for several years and then declare the world polio-free by 2005. The campaign missed the 2000 deadline, which WHO reset for 2002.

The campaign recently has suffered other setbacks. Scientists discovered that some people with impaired immune systems could permanently harbor and transmit the virus, posing a long-term risk of infection to others.

Countries that had made substantial progress against the virus, such as India, have had unexpected outbreaks.

Last year, CDC researchers discovered that an outbreak of polio in the Dominican Republic and Haiti resulted from an unforeseen mutation of the weakened virus used in oral polio vaccine that brought it back to the strength and infectiousness of wild virus.

And in July, a group of New York researchers announced they had synthesized a complete disease-causing polio virus in the lab using mail order materials --- suggesting that the virus can never be considered truly eliminated if it can be re-created.

Control plan sought

Those discoveries, combined with the difficulty of collecting polio virus samples from every lab in the world once eradication is achieved --- a process that was followed for smallpox in the early 1980s --- make eradication impractical, Henderson said.

Instead, he recommended continuing routine vaccination against polio, but reducing the level of spending on international surveillance for cases and on nationwide immunization campaigns in the developing world.

"I'd like to see a soft landing," he said. "If the program is not going to succeed, let us begin to move toward an effective control program."

Committing to routine vaccination for polio also could protect the U.S. population against the possibility that polio could be made into a biological weapon once it is eliminated as a natural disease, Henderson suggested.

Similar fears exist regarding smallpox, which was eradicated in 1980 but continued to exist in two labs in Atlanta and Siberia. Rogue regimes are believed to have obtained some of the Russian smallpox stockpile and to have developed it into weapons.

"It is possible some day that we may go back to routine [smallpox] vaccination simply because of this," Henderson said.

Reaction in the meeting, a gathering of 7,000 physicians who specialize in infectious diseases, was sharply divided. Attendees from the developing world, including Dr. Najwa Khui Bulos of the University of Jordan Medical School, praised the proposal. Immunization experts from the United States did not.