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Global Polio Largely Fading
An Indonesian boy is given polio vaccine in Jakarta, Indonesia. The country kicked off its third nationwide polio immunization campaign in November.
(By Tatan Syuflana -- Associated Press)
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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.
