Polio epidemics in the DRC threaten the eradication effort

Eclipsed by the Ebola epidemic in the Democratic Republic of Congo (DRC), another scary virus is fleeing into this vast, chaotic country: Poliomyelitis Public health experts have worked for months to eradicate the virus but it continues to spread: it has already paralyzed 29 children and June 21 The DRC is "absolutely" the most worrying polio epidemic today, says Michel Zaffran, who heads the Global Initiative for Polio Eradication (GPEI) at the World Health Organization Geneva (Switzerland)

The outbreak also highlights the latest complication on the bumpy road to eradicating polio. poliomyelitis. It is caused not by the wild virus caught by a thread in Afghanistan, Pakistan and possibly Nigeria, but by a rare mutant variant derived from the weakened oral poliovirus vaccine (OPV) virus which has regained its neurovirulence and its ability to spread. As OPV campaigns have led the wild virus to near-extinction, these vaccine-derived circulating polioviruses (cVDPVs) have become the biggest threat to polio eradication. If epidemics do not stop quickly, polio scientists warn that they could get out of control and put in place eradication efforts.

"It is urgent to stop these outbreaks," says epidemiologist Nicholas Grbadly of Imperial College London. . "It's so much more important than controlling the wild virus."

Safe and effective, OPV has long been the workhorse of the eradication effort. But a feature that makes the vaccine so powerful can also be a serious drawback. Shortly after vaccination, the weakened live virus can spread from one person to the other, thus enhancing immunity even in those who have not received the drops against polio. . But in rare cases, in poor countries like the DRC where many children have not been vaccinated, the virus can continue to circulate for years, accumulating mutations until it become dangerous again. The vast majority of cVDPVs are caused by serotype 2, one of three variants of the virus

Almost as soon as cVDPVs were discovered in 2000, the World Health Assembly in Geneva stated that any use of OPV had to stop. was gone. In 2016, with the threat of a greater number of cVDPVs – they now cause more cases of paralysis than the wild virus – the IMEP decided that the wait was no longer a option. At the time, type 2 poliovirus had been eradicated from the wild, which meant that all type 2 viruses came from the vaccine itself. In April of the same year, the 155 countries still using the trivalent vaccine, which targets all three variants of polio, replaced it with a bivalent vaccine whose component type 2 was removed. Nobody knew exactly how this experience would unfold. It was clear, however, that for a few years, some type 2 outbreaks would still occur, those that had started before the "switch", as it was called, but had not been detected or those that had not been detected. caused by the last use of trivalent OPV.

In a virological capture 22, the only way to stop type 2 outbreaks is to use a version of the same vaccine that gave them birth in the first place – in one way or another. Another without seeding another. The inactivated polio vaccine virus can not go back, but it is not enough to stop an epidemic.

To combat these outbreaks, the GPEI created a closely monitored stock of a new monovalent OPV type 2 (OPVm2) only to be released with the approval of the Director General of WHO. If OPVm2 is used wisely and sparingly, it can stop an outbreak without starting a future, says Zaffran. Speed ​​is essential because the immunity of the population to type 2 virus now declines that it was removed from the vaccine, paving the way for an explosive outbreak.