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t’s news no one wanted. But the discovery of another Syrian child paralyzed by polio vaccine viruses in rebel-held Raqqa has the World Health Organization and UNICEF in talks with the Syrian government over whether an emergency vaccination effort can be mounted there.

The new case is the second to be documented in Raqqa — part of a larger polio outbreak in Syria that totals 24 cases of paralysis caused by vaccine viruses. The other cases are in Mayadeen district in the Deir-Ez-Zor governorate of eastern Syria.

The new case, however, suggests the outbreak may be spreading in Raqqa, the self-proclaimed capital of the Islamic State, said Michel Zaffran, director of the WHO’s polio program.

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Officials acknowledge carrying out an emergency vaccination effort there could be exceedingly complicated.

“It is still under discussion due to military activity in the area,” Zaffran told STAT in an email.

If it goes ahead, the outbreak response in Raqqa would attempt to vaccinate 120,000 children under the age of 5 with a special formulation of oral polio vaccine. Health officials would also try to vaccinate 44,000 children with injectable polio vaccine, the type used in the United States and other affluent countries.

An emergency vaccination program for Deir-Ez-Zor and in the southern part of Shadadi district in Hasaka governorate
 is set to begin Saturday. Vaccine for that effort is already in Damascus, Zaffran said.
The first round of vaccinations will target 328,000 children in the two governorates. Already 355 vaccination teams and 61 supervisors are on standby to begin the work. Teams will go house to house in some areas and operate from a fixed position in others.

That, at least, is the plan. But the agencies behind the response know that the shifting winds of war in Syria could pose serious challenges for their work. Vaccine refusal has also been a problem in Deir-Ez-Zor in the past, with some parents reluctant to allow their children to be vaccinated, according to an update released Tuesday by the WHO.

The Syrian cases are caused by vaccine-derived polioviruses — viruses from the oral polio vaccine used in some developing countries. The U.S. discontinued use of the oral vaccine in 2000.

Oral polio vaccine is made using live but weakened viruses. The original version contained components to protect against all three polioviruses, types 1 through 3. Type 2 polioviruses stopped circulating nearly 20 years ago and last year that component was removed from the oral vaccine.

The oral vaccine is highly effective but it has some rare and serious side effects. The weakened viruses can spread from a vaccinated child to other children with whom he or she is in contact.

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If the viruses continue to spread — because children in the area where they develop haven’t been fully immunized against polio — they can mutate to become virulent again. If they spread long enough, they can regain the power to cripple.

The outbreak in Syria is caused by type 2 vaccine viruses.

The oral vaccine that will be used to try to extinguish the outbreak is a single-strain oral vaccine that protects against those viruses.

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