Tuesday, November 15, 2016

Guillaume Chabot-Couture Interviewed by WIRED

Guillaume Chabot-Couture, Sr. Research Manager Polio team at IDM was featured in WIRED article Why It’s So Hard to Tell If a Country Is Really Rid of Polio ---written by Chelsea Leu.

At the time when the article was published, two cases of polio in Nigeria had been confirmed by the WHO, and efforts to quickly ramp back up vaccination efforts were underway. These cases had come approximately two years since the last case, a time when Nigeria appeared to be only a year away from being declared polio free.

A period of three years without cases was recommended in 1996 by the Global Commission for the Certification of Polio, and it requires that surveillance had been working well, without gaps or lapses, during that period of time for a country to be eradicated of polio. At the time, this recommendation was based on modeling work that suggested that if there were three years without cases within a population of 200,000 people, there were approximately 95% chances that transmission had been interrupted. However, the model used in this study assumed perfect information would be collected by health workers, and thus they would know exactly when cases were reported. In practice, however, perfect data is only an ideal.

One of Chabot-Couture’s colleagues conducted a study of the probability of Nigeria being eradicated of polio. The results of the model simulation predicted that the odds of wild poliovirus still in circulation would be very small by mid-2016, if there had not been any lapses in surveillance sensitivity.

The discovery of polio cases in Nigeria after 2 years suggest there were serious gaps in surveillance. Furthermore, an analysis of the genetic sequence of these cases showed that they were most closely related to cases even further back in time, which implied that the gaps in surveillance had been even more severe.

The ongoing insurgency of Boko Haram against the Nigerian army is likely to blame for this surveillance failure. This conflict has created grave population displacement in the region, and vaccination efforts have been interrupted for many years now in certain areas.

Recently, the IDM polio team has modeled what is the minimal population within which the poliovirus can circulate indefinitely, and they found that a population of approximately 200,000 would be sufficient. This is well below the size of the currently inaccessible population in Borno state in Nigeria, and this supports the idea that poliovirus circulated undetected within the inaccessible areas of Borno state.

As Chabot-Couture states in the article the world has achieved the difficult of eradicating a disease only twice so far: smallpox and rinderpest. Since polio cases are only a small fraction of all polio infections, it is difficult to track and stop the circulation of this virus. Nonetheless, much has been achieved so far and there are reasons to be optimistic that this outbreak will be controlled like others have been in the past.