The fight to eradicate polio from the globe has endured recent setbacks, but the head of the worldwide effort said yesterday that the program might be able to halt all transmission of the disease by next year.
Dr. David Heymann, director of the World Health Organization's eradication program, told a Baltimore audience that the key to success will be reaching millions of children with oral vaccine before the rainy season in Africa and Asia next fall, when epidemics usually occur.
"We hope during this low season, polio transmission will be interrupted," Heymann said after delivering the keynote address at the Eighth Annual Conference on Vaccine Research at the Baltimore Marriott Inner Harbor Hotel.
Stopping transmission of the disease would be a major milestone in eliminating the disease worldwide. After that, three years must pass without a single new case before the agency can declare that the virus has been wiped out. Only then can health authorities recommend an end to routine vaccinations.
Polio is a viral disease that initially causes a flu-like illness but can leave victims with paralyzed limbs. It can be fatal when it paralyzes the muscles that control breathing.
The first vaccine, an injected solution developed by Dr. Jonas Salk, was licensed for use 50 years ago. But the oral vaccine, developed several years later by Dr. Albert B. Sabin, has been the principal tool for fighting polio worldwide.
When the current polio campaign was launched in 1988, organizers set a goal of eradicating the disease by 2000. The United Nations' campaign has cost $4 billion, donated by member countries, Rotary International and private foundations.
If it disappears, polio would be just the second disease to be eliminated from the Earth by medical science. The first, smallpox, was declared eradicated in 1980 after an effort that began in the 1960s.
The polio campaign suffered a severe setback in 2003, when Islamic leaders in northern Nigeria urged families not to have their children vaccinated. They said the vaccine was designed to make recipients sterile and possibly give them AIDS, and was a tool in a U.S.-led plan to depopulate the developing world.
Before the boycott, organizers believed that they had cornered the disease in a few strongholds in Nigeria, Egypt, India, Afghanistan and Pakistan.
Last October, Islamic leaders agreed to call off their opposition after receiving assurances from campaign officials that the vaccine was safe, and one leader signaled his support by having his own children vaccinated.
But by then the vaccine boycott had already led to a resurgence of polio in Nigeria, and subsequently across Africa and beyond. In the past 20 months, polio has spread to 16 previously polio-free countries including Yemen and, most recently, Indonesia.
Still, the number of polio cases has dropped drastically since 1988, when 350,000 new cases were identified. Last year, there were 1,185 new cases, up from 784 a year earlier.
Dr. Myron Levine, who heads the University of Maryland's Center for Vaccine Development, said the final stages of eradication are bound to be the hardest.
"It's easy to drop incidence by 90 percent, but getting from 90 to 99 percent is equally hard," said Levine, who worked in the smallpox eradication program. "Then, the final 1 percent is arguably the hardest of all."
In the case of smallpox, the last victims tended to be beggars and other people who were socially and economically isolated.
Stopping polio transmission by next year is achievable but only "if the planets are aligned," Levine said.
"Obviously, we've been to the altar before," he said. "It absolutely can be done but it's very difficult. It needs resources, needs perseverance and needs luck."
The WHO, joined by regional organizations such as the African Union, have been fighting polio by holding mass vaccination each month in countries where the disease is still endemic. On these occasions, parents are asked to bring their children to clinics where the vaccine is administered.
Heymann said the campaign currently faces a funding shortfall of $50 million, which could jeopardize its success. "It's totally feasible to do this if we have enough vaccine to get to the children," Heymann said.
Another potential obstacle is the natural tendency of countries to become lax about vaccinating their children as the disease wanes, he said. This gives the virus a new opportunity to settle into a population.
"Once it hits a population with low immunization coverage, it implants itself," he said.