he World Health Organization said Tuesday that an outbreak of vaccine-related polio cases in Syria has expanded, with 17 children so far paralyzed by the vaccine viruses.
Two weeks ago, there were only two cases.
Test results are pending for another 27 individuals, although some of them may turn out not to be polio cases.
One of the newly confirmed cases is in Raqqa, the self-proclaimed capital of the Islamic State — a factor that could add layers of complexity to an already difficult situation. The other 16 are in Mayadeen district in the Deir-Ez-Zor governorate of eastern Syria.
“The Raqqa case is further being investigated, including to more clearly assess whether there is local circulation in Raqqa as well, or [if this is] an isolated importation from Mayadeen,” Michel Zaffran, director of polio for the WHO, said in an email. “We are also looking at the options for extending the response to Raqqa which … will be more complicated given the current situation.”
Planning is underway to conduct two special rounds of immunization. The first round is expected to begin no later than July 8 and will use a special oral vaccine that targets type 2 polio. The goal is to vaccinate 328,000 children under the age of 5.
A second round, which will use injectable polio vaccine — the type used in the United States — will aim to vaccinate 114,500 children between the ages of 2 months and 24 months.
Zaffran said while speed is of the essence, planning an effective campaign is equally important. The campaign needs to immunize as many children as possible to stop the spread of the vaccine viruses.
The outbreak is an unwelcome setback for the nearly 30-year-long effort to wipe polioviruses from the globe. Before the campaign began in 1988, 350,000 children a year were paralyzed by polio. So far this year only six children have been paralyzed by so-called wild polioviruses, in Pakistan and Afghanistan.
The Syrian cases are caused by vaccine-derived polioviruses — viruses from the oral polio vaccine used in some developing countries. The United States stopped using 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; it costs pennies a dose and is so easy to administer anyone can do it.
But it 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. As the viruses spread from child to child, however, 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 that have been circulating for a couple of years, Zaffran said.
Long-term circulation of vaccine viruses can only occur among children who haven’t been fully protected against polio. That such a development would arise in a war zone is no surprise. In fact, Syria had an outbreak of wild polio in 2013-14, another sign that routine vaccination efforts there have been hampered by the six-year civil war.
Zaffran said the new cases are a tragedy for the children affected and their families, but doesn’t change what health officials need to do operationally.
He said they learned a great deal in battling the earlier outbreak in Syria, “including how to work in these areas and which other partners are on the ground to help us implement.”
“To get our own staff into some of these areas will be very difficult if not impossible, so we will have to work through third parties,” he said.
Operating in places of political instability is nothing new for the Global Polio Eradication Initiative, which 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.