An unexplained shortage of the injectable version of the vaccine slows attempts to kill polio in Afghanistan, Nigeria and Pakistan.
Vaccination rates have fallen dramatically in the last few years, and the conflict is making things worse.
"There is no mercy, we have decided to deal with the refusal cases with iron hands.”
With four more health workers killed this week, trying to eradicate the virus is a dangerous job
More than a dozen polio cases have already been recorded in the largely rebel-held province of Deir al-Zor.