HEALTH & SCIENCE

Polio nearly gone; should vaccine end too?

As the virus is confined to fewer countries, public health officials consider when and if to cease vaccinations.

By Victoria Stagg Elliott, AMNews staff. Jan. 14, 2002. Additional information

Polio is now endemic to only 11 countries and fewer than 500 cases were reported globally in 2001, according to data released by the Centers for Disease Control and Prevention.

But, despite the fact that the last U.S. case of transmission of wild-type polio was in 1979, experts say vaccinations against the disease will still be necessary for years to come.

This caution is due in part to incidents of importation of the disease to the United States from other areas, but also because of transmission connected to live vaccine. Experts also worry about unvaccinated pockets that could become disease reservoirs.

"The big question now is when will we be able to stop using the vaccine," said Arnold Monto, MD, an infectious diseases epidemiologist at the University of Michigan, Ann Arbor. "I think we're going to be conservative about this. Ten years may not be enough."

Of the 152 cases recorded domestically by the CDC from 1980 to 1999, 95% were vaccine-related. There have also been significant outbreaks in the Dominican Republic and Haiti because the virus used in the vaccine mutated and spread -- causing infection among those not vaccinated.

"This adds a complexity to eradicating the polio virus," said Stephen Cochi, MD, MPH, head of the CDC's Global Immunization Division. Dr. Cochi presented the latest data about the status of global polio eradication efforts at the Interscience Conference on Antimicrobial Agents and Chemotherapy in Chicago last month.

"The vaccine virus acted like an actual polio virus and caused an outbreak. This was a warning, and over the long-term, we need to stop using the oral vaccine," he said.

The live vaccine is generally no longer used in the United States, but much of the world still uses it, primarily because it is easier to administer and less expensive. Experts say that globally they expect to see increased use of inactivated vaccine. But they stress that the United States cannot even consider completely ending polio vaccinations until the disease is eliminated worldwide.

Since the World Health Organization launched its Global Polio Eradication Initiative in 1988, cases of polio have plummeted from 350,000 in 1988 to less than 500 in 2001. And, although the year 2000 deadline for eradication was missed, the disease went from being endemic in 125 countries to 11.

"If we could stop polio vaccinations, we could reap the economic benefits of eradicating the disease and get back our investment," said Dr. Cochi. "We're very close to the finish line. The virus is on the run and has fewer and fewer places to hide."

But barriers remain before polio's last refuges are eliminated. Those 11 countries, including Afghanistan, are poor, with weak infrastructures.

"They're difficult countries and require special, sometimes extraordinary measures to deliver a health intervention measure such as the polio vaccine to children," said Dr. Cochi.

Experts also worry about sustaining commitment to eradicate a disease that is rapidly fading into memory. "Complacency can be one of the biggest barriers," said Dr. Cochi. "When a disease is disappearing, people decide it's no longer a priority. In an eradication program, going that last mile can be difficult."

But, in a climate where people are discussing renewed vaccinations for smallpox -- which has been eradicated for years -- ending the polio vaccination is slim, experts say.

"It is very likely the United States will want to continue immunization with the inactivated polio vaccine for the foreseeable future because of the uncertainty, although polio virus would not be one of the agents that would rank high on the list of bioterrorist agents," said Dr. Cochi.

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Global waning

Worldwide polio statistics:

                     Countries

           Number    reporting

          of cases     cases  

          --------   ---------

  1988    350,000       125

  2002      2,019        20

  2001        421        11

Source: Stephen Cochi, MD, MPH, head of the Centers for Disease Control and Prevention Global Immunization Division at the Interscience Conference on Antimicrobial Agents and Chemotherapy, December 2001

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Public Health Dispatch: Update: Outbreak of Poliomyelitis ---Dominican Republic and Haiti, 2000-2001, Morbidity and Mortality Weekly Report, Oct. 5, 2001 (http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5039a3.htm)

WHO Global Polio Eradication Initiative (http://www.who.int/vaccines-polio/)

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Copyright 2002 American Medical Association. All rights reserved.

Additional information

Box: Global waning

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