Public health advocates have long set their sights on wiping out polio worldwide, but recent resurgences of the pernicious disease raise questions about its future eradication.
Several months ago a wild strain of the virus surfaced in a sewer system in Rahat in southern Israel, and now it has reportedly been detected throughout the country. Israel’s government this week launched a nationwide vaccination campaign, attempting to inoculate all children under nine years of age with oral polio vaccine (OPV), a form of the vaccine containing a live, weakened form of the virus. Most of these children were already vaccinated as babies with inactivated polio vaccine (IPV), otherwise known as the dead-virus vaccine. But people who were injected with IPV can still be healthy carriers of the disease and shed the virus in feces.
Scientific American spoke with Bruce Aylward, assistant director general for Polio, Emergencies and Country Collaboration at the World Health Organization, to find out more about the situation in Israel and how recent events there are affecting global efforts to wipe out the disease.
[An edited transcript of the interview follows.]
What is happening in Israel right now?
What we know is that there is widespread detection of a wild polio virus at a number of sites that we have sampled, going back three-plus months. This virus is very similar to a strain that was detected in December of last year in Egypt, in the sewage there. This original virus came from Pakistan. Whether it went into Egypt and then Israel or Israel and then Egypt or [whether it spread via] two separate importations—it is unclear.
The virus has only been found in sewage at this point. There have not been any clinical cases of this so far; no children have been paralyzed. In the past [Israel] has detected [polio] virus from surrounding countries and it has disappeared very quickly, but this time it is persisting for longer. The virus can’t live in the sewage itself and multiply. What we are seeing is persistence of [people excreting] the virus.
How high is Israel's vaccination coverage?
This is a country with quite high immunization coverage—about 94 percentage of coverage. It’s with the inactivated virus, the dead-vaccine virus that Dr. [Jonas] Salk made in the 1950s (versus the live vaccine coverage that [Albert] Sabin developed, which we mainly use in the vaccination program). Since the kids don’t have intestinal immunity, or not very much, the disease is managing to spread.
The reason the oral vaccination is used in the vaccine campaign is it provides intestinal immunity that is so crucial in stopping the person-to-person transmission spread in settings where you might have a high transmission rate of the virus—like in tropical areas or areas with suboptimal sanitation. For a long time in developed countries Sabin’s vaccine was the vaccine of choice, but the drawback was one in a million times a child can get the disease and get paralyzed. It’s very rare, but it’s a risk.
As global progress was made on eradiation, many countries switched to the inactivated vaccine. One country that solely uses inactivated vaccine is Israel.
So the kids who were vaccinated as babies are protected but they can still be carriers?
With IPV you are protected, but you will still shed the virus. Your goal [with vaccination] is the person doesn’t get polio when you vaccinate and also they don’t spread it. With IPV you protect the individual but don’t do as much to protect the gut and protect the community. With OPV you get both protection of the individual and the community.
What's the main challenge to getting more people to take oral vaccine in a situation like this?
In countries where people are no longer using the oral vaccination, people are saying, “Why aren’t we using this vaccine now? Because it can cause paralysis, outbreaks, etcetera.”