November 2, 2005
Planning Polio’s Endgame: A Talk by David Heymann
After a 17-year, $4 billion campaign marked by great successes yet an elusive finale, global public health officials now believe they have driven the poliovirus to the verge of extinction, according to David Heymann, leader of the World Health Organization’s (WHO) polio eradication campaign.
David Heymann confers with colleagues during a 2004 Global Polio Eradication Initiative meeting. (Copyright: WHO / P. Virot)
A recent meeting of the polio eradication advisory committee concluded that it is “biologically feasible” that transmission of wild poliovirus could be interrupted worldwide by the end of 2006, Heymann said in an October 31 address at the Johns Hopkins Bloomberg School of Public Health. After that, a three-year period of intense surveillance would be required before the world could be certified as “polio-free.”
However, polio’s global demise will likely not be quick or easy. “It’s a very complicated endgame,” said Heymann, MD, a former Epidemic Intelligence Service officer with the U.S Centers for Disease Control and Prevention.
Although the U.S. and other industrialized countries have recently switched to an injectable vaccine made from a killed virus, most of the world continues to use the less expensive, easier to administer oral polio vaccine (OPV). But OPV—the workhorse of the global campaign that has reduced polio infections by 99 percent since 1988—can itself cause polio paralysis. For every 2 million to 4 million OPV doses, one case of paralysis can result. This is known as vaccine-associated paralytic polio. In addition, there have been at least five outbreaks of paralytic polio in recent years caused by vaccine-derived polioviruses: viruses in OPV that reverted to a form that could again cause paralysis.
Polio experts therefore agreed in 2004 that once the world is certified polio-free, OPV use would have to stop. The trick is to discontinue its use everywhere at the same time. If one country continues to vaccinate with OPV, it could lead to cases that could eventually spark an outbreak in other countries. “Imagine the complexity of every country in the world stopping all oral polio vaccination on the same day,” said Heymann.
To protect against vaccine-derived poliovirus outbreaks, continued surveillance and stockpiles of vaccines would have to be maintained after OPV’s cessation. And existing samples of the poliovirus, kept in labs worldwide, would have to be destroyed or secured to prevent an accidental or intentional release of the virus.
Heymann acknowledged that it’s a daunting list of demands, but said that political leaders must maintain their interest in the polio endgame. Once the world is declared polio-free, many governments will likely focus on other more immediate health problems, and it will be a challenge to ensure that there are sufficient resources to finish the job, Heymann said.
Despite the strategic obstacles to polio’s endgame, Heymann argued that the campaign, which has reduced polio cases from 350,000 in 1988 to 1,400 this year, must be seen through to the end.
“The challenge for polio today is carpe diem. We must seize the opportunity today,” said Heymann. “We need to complete the job.” —Brian W. Simpson