In another milestone along the long, expensive and sometimes discouraging path to eradicating polio, world health officials announced Wednesday that two of the three strains of wild polio virus have been officially eliminated.
Although approaching the world is another step toward eradication, the effort has taken much longer than expected. When the campaign began in 1988, most public health officials and donors were expecting the battle to end by 2000.
But two major obstacles emerged.
First, millions of families around the world have not dropped their children because of the constant false rumors that the vaccine is a Western conspiracy to sterilize Muslim girls or cause other harm.
In the last two months alone, cases of paralysis caused by mutant vaccines have been reported in the Philippines. , Zambia, Togo and Chad. Since paralysis occurs in only one in every 200 cases of polio, experts suggest that many more children are infected.
Stopping such outbreaks usually requires the vaccination of hundreds of thousands of children with both an injectable vaccine containing a dead virus that cannot mutate and an oral vaccine. The latter contains weakened viruses, which usually cannot cause disease, but provide better protection than killed viruses.
The strain declared by the Global Polio Virus Eradication Commission to be eliminated this week is Type 3 wild polio virus, the last case of which was observed in Nigeria in 2012. Type 2 was declared eliminated in 2015. ; the latter case was discovered in India in 1999.
Type 1, the only wild left strain, circulates only in Pakistan and Afghanistan.
(In the 1950s, the three strains had more evocative names: Brunhilde, Lansing, and Leon. The first was named after a laboratory chimpanzee, the second after the city of Michigan where it was isolated and the third a boy from Los Angeles, The nicknames later came in favor of .)  It takes tremendous effort to monitor for many years before the viral strain is declared extinct. Children can be paralyzed by several other viruses, bacterial brain infections, and injuries to the neck and spine.
To ensure that polio is not the cause, faeces must be sampled from more than 100,000 paralyzed children each year. Thousands of sewage and water samples were taken in 70 countries; the virus can be detected in concentrations of parts per million.
"The certification committee is very, very careful," says Dr. Walter A. Orenstein, polio expert at the Emory Vaccine Center in Atlanta and former director of immunization at the Centers for Disease Control and Prevention .
A dangerous new front has opened up in the last decade in the war against polio.
In countries where the vaccination rate is low, attenuated viruses in the oral vaccine can circulate in the effluent and mutate into what are effectively evil twins.
By accumulating random genetic changes or by exchanging genes with other intestinal viruses such as Coxsackie virus, the viruses can become virulent again and paralyze children who have never been vaccinated.
Over the last two years, outbreaks of cVDPV – meaning "circulating vaccine produced by polio virus" – have affected nearly 20 countries.
Although most of these outbreaks were small and eventually detained, more children are now paralyzed by cVDPV every year than type 1 in Pakistan and Afghanistan.
For example, so far this year, 88 Pakistani and Afghan children were paralyzed by the last wild strain, while 95 children in Africa and Asia were paralyzed by viruses derived from the vaccine.
In order to prevent this, the eradication campaign is taking several steps.
First, health officials are trying to see that every child in the world receives at least one dose of the injected vaccine. It circulates in the blood so that the child can still get – and spread – an intestinal infection but will not be paralyzed by it.
Second, one year after the elimination of polio type 2 globally, the campaign introduced a new "bivalent" vaccine free of type 2 virus attenuated .
But there will be no "monovalent" vaccine alone with type 1 virus weakened, said Michel Zafran director of polio eradication at the World Health Organization.
"Type 2 is so powerful that it dominates the old vaccine," he said. " 3 will not make the current one more immunogenic. "
He was a bureaucratic nightmare, he added, to make every country in the world to import and cool hundreds of millions of new doses of vaccines and safely destroy their old ones.
"We don't need to create a new problem," Dr.
Third, the Bill Foundation and Melinda Gates supports the creation of new oral vaccines, less able to mutate into dangerous forms.
Tightening the loose ends by cutting some nucleotides beyond the portion of the genome that it plays the role of a goalkeeper, leaving it less likely to replace genes with other gut viruses, said Ananda S. Bandyopadhyay, Polio Program Officer at the Foundation.
In addition, determining the genes that create a polymerase that helps the virus to copy means fewer "copy errors" This can be dangerous.
Because the most recent outbreaks are caused by mutant type 2 variants, the foundation has fast-tracked clinical trials on this strain of the new vaccine, Dr. Bandiopadichey said.
"If all goes well, it could be ready by 2020," he said.
New versions of type 1 and type 3 vaccines should follow in a few more years, he said.
The new versions are not intended for routine vaccination, he said, but for an emergency warehouse used to fight fires.