Deployed in twenty -one country, especially in Africa, it could make it possible to stop the outbreaks of cases linked to viruses derived from previous vaccines.
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The relentless war waged by the WHO against polioviruses has led to a paradox. The oral vaccine is massively used in developing countries for its three major assets: its low cost, its easy mode of administration (by drops) and its strong capacity to reduce the interhuman transmission of this pathogen. The reverse of the medal is that the vaccinated person excreates a virus still alive, which can circulate several months from one person not vaccinated to another: he risks becoming virulent again. Several hundred cases of paralysis per year, all linked to such “strains of poliovirus derived from the vaccine”, declare each year, mainly in sub -Saharan Africa.
How to stop the phenomenon, discovered in the early 2000s during an epidemic in Santo Domingo? Hope comes from a new vaccine, designed and developed for ten years by American and European universities, WHO and the Center for the Control and Prevention of Diseases, thanks to funding from the Bill and Melinda Gates.
“A vicious circle”
More than 90 % of cases due to strains derived from the vaccine are caused by one of the three types of poliovirus, type 2. In addition, type 2 which circulates naturally has been eradicated thanks to the WHO program: It was therefore decided to eliminate it from the oral vaccine. But, in 2017 and 2018, in some African countries, several cases of polio have been allocated to type 2 strains. The eradication program was “taken in a vicious circle”, recognizes Maël Bessaud, Poliovirus expert at the Pasteur Institute: to extinguish these new epidemics related to type 2 strains derived from the vaccine … It was necessary to use a vaccination with the type 2 strain!
A new vaccine has therefore been developed. “He uses a strain of type 2 virus whose genome has additional changes, in order to stabilize his less virulent character,” explains Maël Bessaud. After being assessed in vitro and a small group of volunteers, this vaccine obtained an authorization for general use in October 2021. For the time being, only one company factory, Biofarma, in Indonesia.
“As of June 28, 370 million doses of this new vaccine had been administered in twenty -one country: Nigeria, Liberia, Sierra Leone, Tadjikistan …”, says Maël Bessaud. The first surveillance data show that he did not acquire of mutations leaving a drift to a more virulent character .