Is it the end of an era for eradication?

CHICAGO — The eradication of smallpox has been widely hailed as the most significant public health achievement of the 20th century.

The successful effort caused public health officials to believe that other diseases could be eradicated as well. This paved the way for the World Health Organization (WHO) to declare in 1988 that poliovirus would be the next disease for eradication.

WHO originally set a 2000 target date for polio’s eradication, but that date has since been pushed to 2005. With just a few hundred cases reported annually it seems likely that WHO will reach this goal.

Full eradication of a disease requires intensive global political commitment and funding, making eradication both labor-intensive and expensive. In an era when public health programs must compete for scarce funding with programs that promise a more visible return on investment, some public health officials are calling for an end to eradication programs. Supporters of eradication efforts are reluctant to see their programs disappear, however, and have countered that these programs have come too far to turn back now.

When the polio eradication effort was announced, there were approximately 350,000 cases per year affecting nearly every country in the world. By contrast, in 2001 there were fewer than 500 cases in 10 countries and efforts are still ongoing to reduce that number.

After a research team from the State University of New York at Stony Brook constructed a poliovirus from available chemical compounds and information gathered from the Internet, some wondered if eradication was even desirable.

The case against eradication

The era of eradication has been marked by the tremendous success of eliminating smallpox, but also by glaring failures. Between 1915 and 1932, the U.S. led an unsuccessful effort to eliminate yellow fever. Later, efforts to stop yaws and malaria in the 1950s and 1970s also failed.

“The fact is, only one disease has been successfully eradicated [and] four others have failed,” said Donald A. Henderson, MD, here at the 40th Annual Meeting of the Infectious Disease Society of America.

Current eradication efforts are now facing obstacles that were unknown at the onset of the program that have raised doubts about their plausibility, added Henderson, director of the Johns Hopkins University Biodefense Program. The discovery of vaccine-derived paralytic poliomyelitis in the Philippines, Haiti, Madagascar, Egypt and the Dominican Republic has raised questions whether vaccination with polio vaccine can ever end. The cases appeared to be circulating for years before their discovery, health officials claim.

Additionally, there have been at least 10 reports of individuals with immunodeficiencies who shed poliovirus for several years after receiving the vaccine. In one case, a man was still excreting poliovirus nearly 20 years after being vaccinated and the vaccine virus itself has proven virulent in animal studies.

Proponents of eradication claim that oral polio vaccine will some day be stopped in order to prevent vaccine-derived from entering the population. But this is problematic, according to Henderson, because if outbreaks from shed virus did occur, the oral polio vaccine would be the only thing to stop them.

But perhaps the most practical reason to halt eradication programs is because of the potential for turning the pathogen into a bioterrorist agent. Given the current climate of uncertainty, it would be necessary either to continue polio vaccination or to have enough vaccine in storage to contain outbreaks. According to Henderson, this might require maintaining a manufacturing facility.

“The threat of a deliberate release of whatever agent that might be on the eradication agenda now poses a serious threat, and I’m afraid it will continue to do so as far in to the future as we can presently foresee,” he said.

In 1998, poliovirus was endemic in about 50 countries and that number dropped to 10 in 2001. By the end of this year, the CDC and WHO hope to further reduce the number of polio endemic countries to five: Pakistan, Afghanistan, India, Nigeria and Egypt. There is already intensive surveillance and public health officials will be monitoring for breakout cases.

“This is not an effort that is on its last legs,” said Stephen Cochi, MD, director of the Global Immunization Division of the CDC, in response to Henderson’s comments.

WHO is now searching for funds to finish eradicating polio and speculation has risen that measles, already vanquished from the Americas and Europe, will be next.

However, if the threat of bioterrorism is not dealt with adequately, diseases like polio and measles could become threats to national security. On the other hand, is it too late to stop eradication programs when the only obstacle to eradication is increased access to vaccination?

For more information:

• Henderson D. The Joseph Smadel Lecture: eradication of viral diseases. Presented at the 40th Annual Meeting of the Infectious Disease Society of America. Oct. 24-27, 2002. Chicago.