Polio Cases Reemerge In Syria, But The News Isn’t All Bad

The small outbreak appears to be traced to a rare consequence of the oral polio vaccine

A Pakistani child receiving the oral polio vaccine — BANARAS KHAN/AFP/Getty Images
Jun 08, 2017 at 5:08 PM ET

The global campaign to eradicate the infectious disease polio — now decades in the making — has encountered yet another setback.

On Thursday, the World Health Organization confirmed that Syria is dealing with an outbreak in the eastern Syria region of Deir-Ez-Zor. There have been at least three cases detected, all in children. In two cases, found in March and May, the children were afflicted with an acute form of paralysis often caused by the virus, while the third case was found in a healthy child who lives nearby.

It’s the first polio outbreak to have been detected within Syria since 2014. But unlike then, the current spate of cases have been caused by a mutated version of the virus used in some vaccines rather than a wild polio strain. These vaccine-derived polioviruses, as they’re called, are a rare consequence of the oral polio vaccine, which uses a weakened but still “alive” form of the virus.

Particularly in communities where vaccine rates are low, these weakened viruses can survive long enough to mutate back into a dangerous form and infect unprotected people. Other vaccines, which use completely inactivated polioviruses, don’t carry that risk.

With either wild or vaccine-deprived polio outbreaks, the best strategy is to go in and vaccinate everyone else as quickly as possible. WHO, in collaboration with local authorities and health agencies, is in the midst of launching an emergency vaccination program that will target up to 200,000 children, according to STAT. And they’re actively looking for other possible cases.

All things considered, the news could be much worse. The country continues to appear free of any naturally occurring poliovirus, and even the 2013-2014 outbreak is believed to have been caused by a strain imported from another country, Pakistan.

Currently, Pakistan and Afghanistan are the only two countries where transmission of wild polio is still happening. As of this early June, though, the numbers are still very encouraging. So far this year, there have only been five confirmed cases of wild polio in the world. And should that trend continue, it’d be a step down from the 33 cases detected in 2016.

The WHO’s global polio eradication initiative has also begun to take steps to prevent more vaccine-derived cases. Ultimately, they hope to remove all oral vaccines from the routine vaccination programs in needed countries, but in April 2016, they enacted a stopgap solution, switching its formula.

Instead of the vaccine carrying all three major types of polioviruses, it now only carries type 1 and 3. Type 2 wild polio was declared eradicated in 1999, but so long as it remained in vaccines, it could momentarily reemerge. And indeed, the majority of vaccine-derived polio outbreaks have been traced to Type 2 polio. But given the timing of this latest outbreak in Syria — also caused by type 2 — it’s clear the change in vaccines will take some time before it begins to fully kick in.