WHO’s relentless war against polioviruses has led to a paradox. The oral vaccine is widely used in developing countries for its three major advantages: its low cost, its easy method of administration (by drops) and its strong capacity to reduce the human-to-human transmission of this pathogenic agent. The other side of the coin is that the vaccinated person excretes a still living virus, which can circulate for several months from one unvaccinated person to another: it risks becoming virulent again. Several hundred cases of paralysis per year, all related to such “vaccine-derived poliovirus strains”occur every 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 over the past decade by American and European universities, the WHO and the Center for Disease Control and Prevention, with 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, the type 2 which circulates naturally has been eradicated thanks to the WHO program: it has therefore been decided to eliminate it from the oral vaccine. However, in 2017 and 2018, in some African countries, several cases of poliomyelitis were attributed to type 2 strains. The eradication program found itself caught in a vicious circle »recognizes Maël Bessaud, poliovirus expert at the Institut Pasteur: to extinguish these new epidemics linked to type 2 strains derived from the vaccine… it was necessary to resort to vaccination with the type 2 strain!
A new vaccine has therefore been developed. “It uses a strain of the type 2 virus whose genome has additional mutations, in order to stabilize its less virulent character”, explains Maël Bessaud. After being evaluated in vitro and in a small group of volunteers, this vaccine obtained from the WHO, in October 2021, an authorization for general use. For now, only one company manufactures it, Biofarma, in Indonesia.
“As of June 28, 370 million doses of this new vaccine had been administered in twenty-one countries: Nigeria, Liberia, Sierra Leone, Tajikistan…”, says Maël Bessaud. The first surveillance data show that it has not acquired any mutations giving rise to fears of a drift towards a more virulent character.