The strain 3 of the virus is declared as eradicated, but this announcement, made official during the World Day against polio, Thursday, October 24, is tarnished by the risk related to the oral distribution of the vaccine in several countries.
The polio virus is putting a foot in the grave again. Unless major surprise, the commission for certification of eradication, a group of experts at the World Health Organization (WHO), will make the announcement on the World Day against polio, Thursday, October 24: strain 3 of the virus has permanently disappeared from Earth's surface. This strain has not been detected since 2012. After strain 2, officially eradicated in 2015, it is the second agent of the virus to be sentenced to life imprisonment. Only his third agent, strain 1, is still in the wild, more exactly in two countries: Pakistan and Afghanistan.
The other good news of this World Polio Day is on the African continent: no more of the three strains of wild (classical) virus have been circulating since 2016. "It's a fantastic achievement," says Oliver Rosenbauer, spokesperson for the polio eradication program for WHO. Thirty years ago, this virus paralyzed more than 1,000 children every day around the world. For the year 2018, only 19 cases of paralysis related to the wild virus were identified.
Circulation of vaccine viruses
Viewed from this angle, the victory seems close. But on the ground, the last kilometers to eradication are a nightmare. Because the problem of wild virus has replaced another: the circulation of vaccinal (mutated) viruses. While vaccines have helped to reduce paralysis by more than 99%, some offer the possibility of a second life for the virus. These are oral vaccines, which contain so-called "attenuated" polioviruses. If they have lost their virulence in the laboratory, these viruses are still alive. When they are ingested by children, in the form of drops, they trigger the production of antibodies in the intestines, to detect and then neutralize these pathogens directly upon their arrival in the body. They thus make it possible to stop the human-to-human transmission of the pathogen.
Polioviruses are particularly tough, they can survive for years in streams
The problem is that some of these vaccine viruses end up in the stools of the vaccinated people and continue on their way into the environment. However, polioviruses are particularly tough, they can survive for years in streams, and eventually move to other intestines. During this time, these viruses can very rarely undergo mutations allowing them to recover the virulence of yesteryear. Therefore, it suffices that they cross the road of non-immune persons to cause, in about 1 case out of 100, paralysis. In 2018, no fewer than 86 people were paralyzed by these mutant strains. That's 4.5 times more than the victims of the wild virus. The 2019 report will be even darker: in mid-October, there were 111 people paralyzed by vaccine strains, including 97 by strain 2, which has not been in the wild for a decade.