Polio: Does the outbreak in Israel endanger the international efforts to eradicate the virus?

An expert from the World Health Organization sheds light on the significance of finding the polio virus in Israel's sewage system
by Dina Payne from Rome (translated from the Scientific American website www.sciam.com)

Public health experts have long been striving to eradicate the polio virus worldwide, but the deadly disease's extinction has been called into question by recent outbreaks.

A few months ago, a wild strain of the virus emerged in the sewage system of Rahat in the south of the country, and now there are reports of its detection throughout the country. The Israeli government has launched a nationwide vaccination campaign, in an attempt to vaccinate all children under the age of nine with the oral polio vaccine (that is, the oral polio vaccine, known as OPV), a form of the vaccine that contains a live but weakened virus. Most of these children had already been vaccinated as infants with the inactivated polio virus (IPV). But people who received injections of IPV can still be healthy carriers of the disease and spread the virus in their feces.

Scientific American interviewed Bruce Aylward, Deputy Director General for Polio, Emergencies and Cooperation at the World Health Organization (WHO), to understand the situation in Israel and how recent events may affect global efforts to eradicate the disease.

Here is an edited version of the interview:

What is happening in Israel right now?

What we do know is that the virus was detected in several sampled sites, already three months ago and more. This virus is very similar to the strain identified in December 2012 in the sewage system in Egypt. The original virus came from Pakistan. It is not clear whether it first penetrated into Egypt and from there into Israel or vice versa or [that it spread] in two separate events.

Currently the virus is only found in the sewage system. There have been no cases of illness so far, and no child has been paralyzed. In the past, Israel detected polio viruses that originated in neighboring countries, and they quickly disappeared. But this time the virus is present for a long time. The virus cannot live and reproduce in sewage. What we see is a prolonged presence of the virus [due to secretion by carriers].

How comprehensive is the vaccination coverage in Israel?

This is a country with high vaccination coverage - about 94%. This is a vaccine with the killed virus, Developed by Dr. [Jones] Salk in the 50s (As opposed to covering the live virus vaccine developed by [Albert] Sabin, which is the primary vaccine used by the WHO in its immunization programs). Since children do not have an immune response in the intestines, or at most a weak response, the disease manages to spread.

The reason the oral component is used in the current vaccination campaign is that it stimulates an immune response in the intestines, which is essential to stop the transmission of the virus from person to person in areas where there are high chances of infection, such as tropical areas or places with suboptimal sanitation conditions. For a long time, developed countries chose Sabin's component, but the downside was that one in a million children might contract the disease and suffer paralysis. This is very rare, but it is a risk.

As the world moved towards eradicating the virus, many countries switched to the lethal component. One of the countries that only uses the dead component is Israel.

So children vaccinated as babies are protected but may still be carriers?

Those vaccinated with the IPV vaccine are protected, but they can still spread the virus. Our goal [with vaccines] is that people will not get polio when they are vaccinated and also that they will not spread it. The IPV vaccine protects the individual, but not so much the digestive system and the community. Through the OPV vaccine you get protection for both the individual and the community.

What is the main challenge in getting more people to take the oral component in such situations?

In countries where people no longer use the oral ingredient, the claim is: "We don't use this ingredient now because it causes paralysis, outbreaks of the plague, and so on."

The killed ingredient has no serious side effects. The oral component involves extremely rare but real risks. The most common and expected side effect [of the oral component] is vaccine-associated polio (VAPP). The risk is less than one in a million and is mainly related to the first dose of the vaccine. The [live] component by itself does not cause paralysis [in cases of VAPP] because the component contains a weakened form of the virus. But the virus in the component multiplies in the child's body and returns to a violent state.

What did other countries do in a situation like the one in Israel?

Other countries that use IPV, such as the Netherlands, have used OPV to contain an outbreak due to infiltration of the volatile into their territory. OPV is still the best method to quickly stop an outbreak of the virus.

It is a game of Russian roulette to allow the virus to spread in the country knowing that there are children at risk. Even with 94% vaccination coverage [by injecting the dead virus] there are still 6% of the population who can contract the virus, and there are risks among the remaining 94% as well. If the infection is not stopped there will be cases of paralysis.

How does the disease spread through the feces?

Think about the last time you were in a public restroom and the number of people who didn't wash their hands. Although we want to pretend that the level of hygiene is amazing all over the world, we know that everyone's personal hygiene is not perfect. Polio is one of those viruses that only requires a tiny dose to become infected. If the virus is present in the environment, there is a high chance of being exposed to it. It spreads contagiously from the feces to the mouth.

How worried are you that the virus will spread outside of Israel?

At the moment, any situation of prolonged spread of the virus anywhere in the world is a matter of concern and must be treated as a health emergency in the country itself and in the neighboring countries. The virus is a silent hitchhiker that moves in the intestines of vaccinated people. People who have been vaccinated against IPV can be carriers of the virus without even knowing it. The concern arises when there is a prolonged presence of the virus, as there is now, and its spread. In Israel, if they don't stop it, it will indeed spread, we don't want there to be a renewed infection in neighboring countries that have problems with their vaccination campaigns.

Polio recently emerged in Somalia. How is the breed in Israel different from the one in Somalia?

In Somalia it is an African species. Both are viruses of serotype 1. There are three types of polio. This is the first year in history that we have seen only one type of polio. We saw the last Type 3 in November 2012 in Nigeria. Type 2 is no longer seen at all. This is the first year in which more than six months have passed without a type 3 virus. The Israeli virus originated in Pakistan, in South-Central Asia. The virus in Somalia arrived via a West African route that passes mainly through Nigeria.

Where do global efforts stand to eradicate polio worldwide?

We are closer than ever. We now only deal with one type of the virus and see fewer subtypes of it. In Pakistan, Nigeria and Afghanistan, the three areas of the world where polio still exists, the prevalence [of the viruses] is lower than ever and the number of patients is lower than ever. Although Israel has been reinfected, it has stopped [the disease] many times in the past and it will stop it again.

Although Somalia has been reinfected, and there is already a large outbreak there, it has also been infected many times in the past. The key [to eradicating polio] is what is happening in Nigeria and Pakistan. Afghanistan simply receives the virus from the border with Pakistan.

Doctors Without Borders recently left Somalia because of the violence there which poses a risk to their people. Does this harm Somalia's chances of taming the polio outbreak in its territory?

The main significance of the departure of Doctors Without Borders is related to the broader health services. The organization is one of the few healthcare providers that provide basic services in certain areas of the country. In terms of polio eradication, if Doctors Without Borders or other organizations stay there, it helps. But in two hours of training, anyone can give an [oral] vaccine to children.

for further reading

The birth of a vaccine in the Cold War