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Polio outbreak in Syria poses vaccination dilemma for WHO

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Vaccinating too few children in Syria against polio because the six-year-old war there makes it difficult to reach them risks causing more cases in the future, the World Health Organization (WHO) said on Friday, posing a dilemma after a recent outbreak.

Two children have been paralyzed in the last few months in Islamic State-held Deir al-Zor in the first polio cases in Syria since 2014 and in the same eastern province bordering Iraq where a different strain caused 36 cases in 2013-2014.

Vaccinating even 50 percent of the estimated 90,000 children aged under 5 in the Mayadin area of Deir al-Zor would probably not be enough to stop the outbreak and might actually sow the seeds for the next outbreak, WHO's Oliver Rosenbauer said.

Immunisation rates need to be closer to 80 percent to have maximum effect and protect a population, he told a briefing.

"Are we concerned that we're in fact going to be seeding further future polio vaccine-derived outbreaks? ... Absolutely, that is a concern. And that is why this vaccine must be used judiciously and to try to ensure the highest level of coverage," Rosenbauer said.

"This is kind of what has become known as the OPV, the oral polio vaccine paradox," he said.

The new cases are a vaccine-derived poliovirus type 2, a rare type which can emerge in under-immunised communities after mutating from strains contained in the oral polio vaccine.



The Global Polio Eradication Initiative has a long history of operating in places of political instability and has been successful in the past in negotiating so-called “days of tranquility” in which ceasefires allow vaccination teams to reach otherwise hard-to-reach children.

In mid-May, an anonymous contributor reported to the online disease surveillance system ProMED that there was a cluster of children who had suffered what’s called acute flaccid paralysis in Syria. Sudden onset of paralysis can be caused by a number of things, but in parts of the world where polio is still a threat, it must be ruled out when such cases arise.

The polio program has received reports of 58 children in the region who have recently experienced acute flaccid paralysis. Testing showed the vaccine viruses were not responsible in 11 of these cases, but further testing remains to be done on samples from the others.

Getting samples from Deir-Ez-Zor to laboratories in Damascus and Ankara that can do the testing isn’t easy or quick.

“This is still a work in progress,” Zaffran said. “We have samples that have reached the lab that have tested negative. We have samples that have reached the lab and have not yet been completely tested. And we have samples that have been collected that are still stuck in Syria and are not yet transported.”

Oral polio vaccine is made using live but weakened viruses; the original formulation contained components to protect against all three polioviruses, types 1 through 3. Type 2 polioviruses stopped circulating nearly 20 years ago.

While highly effective, the oral vaccine has some rare but serious side effects. The weakened viruses can spread from a vaccinated child to other children with whom he or she is in contact, also passively vaccinating them. But as the viruses spread from child to child they can mutate to become virulent again, regaining the power to cripple.

That’s what has happened in Syria. And there may be more cases, Zaffran acknowledged.



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