In another milestone on the long, expensive and sometimes daunting path to polio eradication, global health authorities announced on Wednesday that two of the three strains of the wild polio virus had been officially eliminated.
Although this brings the world of extinction a step closer, the effort has taken much longer than ever expected. When the campaign began in 1988, most health authorities and donors expected the fight to end by the year 2000.
However, two major obstacles came to light.
First, millions of families around the world have not given their children the drops because of persistent false rumors that the vaccine is a Western plan to sterilize or harm Muslim girls. Second, in some countries, viruses used in the oral vaccine itself have mutated into a form that can be passed on to diapers and wastewater and can paralyze unvaccinated children. This has contributed to the fear of the oral vaccine, although complete vaccination is the only protection against such mutant viruses.
In order to stop such outbreaks, hundreds of thousands of children usually need to be vaccinated with both the injectable vaccine containing an unmutable virus and the oral vaccine. The latter contains debilitated viruses that normally do not cause disease, but offer better protection than killed viruses.
The strain, which this week was declared eliminated by the Global Certification Commission for poliovirus eradication, is the wild poliovirus type 3, the last case of which was seen in Nigeria in 2012. Type 2 was created in 2015 for eliminated explained; The last case was discovered in 1999 in India.
Type 1, the only remaining wild tribe, occurs only in Pakistan and Afghanistan.
(In the 1950s, the three tribes had more meaningful names: Brunhilde, Lansing and Leon. The first was named after a lab chimpanzee, the second named after the city of Michigan, where he was isolated, and the third after a deceased boy Los Angeles. The nicknames later fell into disgrace 19659002] Enormous, multi-year surveillance efforts are needed before a virus strain can be declared extinct Children can be affected by several other viruses, by bacterial brain infections as well as by neck and neck Spinal injuries are paralyzed.
To ensure that polio was not the cause, more than 100,000 paralyzed children were asked to have stool samples taken every year, and thousands of samples were taken in 70 countries and the virus can be detected in ppm concentrations.
"The certification commission was very, very careful", say Walter A. Orenstein, polio expert at the Emory Vaccine Center in Atlanta and former vaccine director at the Centers for Disease Control and Prevention .
In the last decade, a dangerous new front has opened up in the fight against polio.
In countries where the vaccination rates are low, the weakened viruses in the oral vaccine can circulate in the wastewater and mutate into the effectively evil twins.
By accumulating random genetic alterations or by exchanging genes with other intestinal viruses such as coxsackie virus, viruses can become virulent again and paralyze children who have not been vaccinated in the last two years.
cVDPV outbreaks – which stands for "circulating vaccine-derived polio virus" – hit nearly 20 countries.
Although most of these outbreaks were minor and precipitated over time, in Pakistan and Afghanistan, more children are paralyzed each year by cVDPV than by type 1.
For example, to now in This year, 88 Pakistani and Afghan children are paralyzed by the last wild tribe, while 95 children in Africa and Asia are paralyzed by vaccine viruses.
To prevent this, several steps are being taken as part of the eradication campaign.
First, health officials try to see every child in the world get at least one dose of the injected vaccine. It circulates in the blood so that a child can still get and spread an intestinal infection, but is not paralyzed by it.
Second, the campaign launched a new "Divalent Vaccine Without Type 2 Virus " weakened one year after the worldwide elimination of Type 2 polio .
However, there will be no "monovalent" vaccine with only type 1-debilitated virus, said Michel Zaffran director of the Department of Polio at the World Health Organization.
"Type 2 was so strong that it dominated the old vaccine," he said. "Removing Type 3 does not make the current guy more immunogenic."
It has been a bureaucratic nightmare to persuade every country in the world to import and cool hundreds of millions of new vaccine doses and safely destroy the old ones.
"We do not have to create a new problem", Zaffran said:
Third, the Bill and Melinda Gates Foundation supports the creation of new oral vaccines that can mutate less into dangerous forms. Of the part of the genome that acts as the gatekeeper, it is less likely to swap genes with other gut viruses, said . Ananda S. Bandyopadhyay, Polio Program Officer of the Foundation.
In addition, r means rearranging the genes that generate the polymerase, which helps the virus copy itself, less "copying errors." It may be dangerous.
Since the recent outbreaks were caused by mutated versions of Type 2, the Foundation has accelerated clinical trials of this strain of the new vaccine, Dr. Bandyopadhyay.
"If all goes well, it could be ready by 2020," he said.
Novel versions of Type 1 and Type 3 vaccines should follow in a few years, he said.
The new versions are not intended for routine vaccinations, but for emergency supplies to fight outbreaks.