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 Health & Beauty | December 2005 
Global Polio Largely Fading
 David Brown - Washington Post
| | An Indonesian boy is given polio vaccine in Jakarta, Indonesia. The country kicked off its third nationwide polio immunization campaign in November. (Tatan Syuflana/AP) |
The 17-year effort to eradicate polio from the world appears to be back on track after nearly unraveling in the past three years.
A new strategy of using a vaccine targeting the dominant strain of the virus appears to have eliminated polio from Egypt, one of six countries where it was freely circulating. That approach is on the verge of doing the same in India. Twenty-five years ago, India had 200,000 cases of paralytic polio a year. A decade ago, it was still seeing 75,000 cases annually. Through November this year, it recorded 52.
Such dramatic successes, many the result of a more potent formulation of polio vaccine, have once again made eradication of the paralyzing viral disease a realistic goal. Only one human disease - smallpox - has ever been wiped out, and that was almost three decades ago.
Intensive immunization campaigns targeting tens of millions of children in Africa have suppressed polio transmission in countries where it reappeared after the continent's most populous nation, Nigeria, halted universal polio vaccination in 2003.
The end of 2005 had been the latest deadline for polio eradication. The initiative, started in 1988, had a polio-free world by 2000 as its goal. No new deadline has been set, and success may depend, in part, on raising $200 million for more vaccination campaigns.
Nevertheless, the organizers and those funding the eradication initiative are more confident.
"I don't think there's any question that it's going to succeed. The question is how long," said William T. Sergeant, a Rotary International official. "The countries that were reinfected - they were places where we had stopped polio before, and we can stop it again."
A civic club with 33,000 chapters worldwide, Rotary is a co-leader of the eradication campaign, to which it has contributed $600 million and tens of thousands of volunteers.
"The risk now is Nigeria - and losing the commitment in other countries. But we're confident now that Nigeria will get the job done," said David L. Heymann, chief of the polio eradication program at the World Health Organization, which is directing the initiative.
The new "monovalent" vaccine appears to have been close to a magic bullet in boosting immunity to polio in a half-dozen areas of extremely high population density.
"This is the big development, without a doubt," said R. Bruce Aylward, a Canadian physician and WHO's chief eradication strategist.
The effort to eliminate polio has taken longer and proved harder than the eradication of smallpox, which took 10 years and ended in 1978. One of the main reasons is that most polio infections are not apparent, while smallpox causes a dramatic rash that makes identifying victims fairly easy.
Although polio virus does its damage in the spinal cord, it infects the body through the intestine and spreads most easily in crowded populations with poor sanitation.
In only 1 in 200 infections does it cause paralysis. In other cases, it produces only fever and diarrhea, or no symptoms. Consequently, polio virus can be carried "silently" into a polio-free population and spread before it is recognized.
That is what happened when the Islamic states of northern Nigeria stopped immunizing children in 2003 because of rumors that the oral vaccine caused sterility and was part of a Western campaign against Muslims.
Between January 2003 and July 2005, 18 polio-free countries were reinfected with virus that originated in northern Nigeria.
Analysis of the poliovirus genes - which accumulate mutations at a steady, known rate - allowed scientists to trace the route, and even the timing, of the microbe's spread.
Work done at the Centers for Disease Control and Prevention by Olen M. Kew and Mark A. Pallansch showed that virus from northern Nigeria was carried into Chad and several neighboring countries in 2003. From Chad one strain moved to Sudan in late 2003 or early 2004, and from there to Saudi Arabia. From Saudi Arabia it was carried to Indonesia, where on March 13 this year, polio was diagnosed in an infant boy in West Java - the first Indonesian case since 1995.
Reinfection occurred because these countries had not maintained adequate immunization rates in young children.
During the same period, three other polio-free countries - Angola, Lebanon and Nepal - were reinfected with virus that originated in northern India.
In all these countries - and in northern Nigeria, where politicians and clerics now support polio vaccination - intensive immunization campaigns have resumed.
Last month, WHO experts confirmed that 10 reinfected African countries - Benin, Burkina Faso, Cameroon, Central African Republic, Chad, Ivory Coast, Ghana, Guinea, Mali and Togo - have reported no cases since late June. That strongly suggests virus transmission has been stopped.
The trans-Africa outbreak had many arresting features - post-9/11 suspicions of the West in Muslim regions, political jockeying in Nigeria and a humanitarian disaster in Sudan that accelerated the spread of the disease.
"What the world wasn't looking at was what was happening in Egypt and India," Aylward said recently in his office in Geneva.
Vaccination campaigns were being run every few months in those countries. They were reaching 90 to 95 percent of children younger than 5. Yet polio kept circulating.
"This was a much bigger risk than Nigeria because we had a potentially fatal flaw in the program," Aylward said.
The solution came when Aylward and his colleagues realized that - ironically - they would get better results with a much simpler version of the vaccine.
There are three types of polio virus - 1, 2 and 3 - that differ slightly. No type 2 virus has been detected since September 1999; it appears to be eradicated. Type 3 is disappearing fast; it occurs only in Nigeria, Niger, northern India and Afghanistan.
Oral polio vaccine contains weakened strains of all three. That would not seem to be a problem - except it turns out it is.
A dose of oral vaccine - two drops - contains about 1 million type 1 viruses, and about 100,000 type 2 and type 3 viruses. In the human intestine, these viruses compete with one another in producing "protective immunity" against the virus.
After one dose of oral vaccine, only about 25 percent of babies were protected against type 1 polio virus. That rises to more than 90 percent - but only after multiple doses. In two Indian states where polio is endemic - Uttar Pradesh and Bihar - nearly 750,000 babies are born each month. That results in a pool of unvaccinated "susceptibles" that constantly numbers in the millions.
Studies showed, however, that giving a vaccine containing only type 1 virus to infants produced immunity in 80 percent after a single dose. Armed with that understanding, WHO found vaccine makers willing to make a monovalent type 1 vaccine, and in November 2004 it ordered 50 million doses.
In six months, the reformulated vaccine got through the process of testing, approval and licensing by regulatory agencies in France, India and Belgium, where it is made.
"No quality controls were skipped. Everybody just gave us their highest attention," said Shanelle Hall of the supply division of UNICEF, the agency that provides most of the vaccine.
Since the vaccine went into use in Egypt this spring, polio has disappeared there. UNICEF has ordered 600 million doses and plans to use it throughout much of Africa.
Next year, India may be free of polio. One former hotbed - Bombay - already is.
Since April, no polio virus has been detected in that city's sewage. That is indirect evidence the virus is no longer carried by any of its 12.7 million residents - undoubtedly for the first time in history. |
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