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It is the news disease-watchers feared: 22 suspected cases of polio have been reported in north-east Syria, and many more may be infected, spreading the virus. This is bad news for Syrians, and for the world. Polio is on the brink of eradication, and if the ongoing war in Syria frustrates efforts to smother this outbreak, the disease could make a wider comeback.
A massive vaccination drive across the entire region should be under way within weeks, say officials at the World Health Organization in Geneva, Switzerland. However, the real problem, and probable source of the Syrian outbreak, is north-west Pakistan, where polio vaccination is banned by local leaders.
Polio is an intestinal virus spread mainly in sewage. If the virus is present in the community, exposure increases if sanitation systems are destroyed, or people flee to crowded, unsanitary refuges. More than 6 million Syrians are now refugees within or outside Syria, and half are children who may not have been vaccinated.
Disease watch
In 2012, the WHO organised an Early Warning Alert and Response Network (EWARN) system in Syria, an emergency network of public health professionals charged with sounding the alarm if they came across any unusual diseases. This August, they started seeing paralysed children in the Deir al-Zour province near Syria's border with Iraq, a region of fierce fighting.
On 17 October, Syria's national polio lab in Damascus told the WHO that tests showed the cause was probably polio. Rebel-held areas have also reported polio cases.
Samples will be flown from Damascus to the regional polio reference lab in Tunisia in days for genetic sequencing, says Bruce Aylward, head of polio eradication and emergency response at the WHO. That will show whether the outbreak is a live vaccine virus that has regained its virulence, or a wild virus.
"This looks to me like wild virus," says Aylward, partly because most of the affected children are under 2 years old, and haven't been vaccinated due to the country's two-year civil war. The virus causes paralysis – the main symptom – in only 1-in-200 non-immunised people it infects. "That means hundreds of kids are infected," he says.
Backwards step
Syria eliminated polio in the 1990s, and before the war the country had generally high vaccination levels. It is easier to control outbreaks in such places than in countries where polio has never stopped circulating, says epidemiologist Nick Grassly of Imperial College London. But conflict makes rolling out vaccination programmes difficult and dangerous.
Syrians that have fled to refugee camps outside the country automatically get vaccinated against polio, but it is harder to reach those that have not gone to an organised camp. The polio vaccination drives planned for the coming weeks will also offer other basic health measures, such as measles vaccine, making parents more likely to come forward.
Major vaccination drives for all children were already planned during November and December in Turkey, Jordan, Lebanon, Israel, Iraq, Egypt and the Palestinian territories. The WHO is now working with those countries to synchronise the vaccinations in the hope this will minimise the chance that children travelling from one place to another will be missed.
Sequencing clues
Once the outbreak virus is sequenced, it will be possible to trace its route into Syria and to identify any other at-risk areas. For example, it should be possible to determine whether the virus came directly from Pakistan or whether it is a Pakistani virus that arrived in Syria via Egypt and Israel, where the virus was found in sewage earlier this year.
Polio has never stopped circulating in Pakistan, Nigeria and Afghanistan. Vaccination is making progress in Nigeria, where case numbers are half what they were this time last year, and in Afghanistan, where they are less than a third – a mere seven cases. But Pakistan has shown little improvement, as a ban on vaccination by Islamist leaders in Waziristan remains in place. Health workers doing polio vaccination elsewhere in Pakistan have been murdered.
"The Syrian outbreak shows why eradication is the solution for this virus," says Aylward. "As long as it persists, if children are non-immunised, it will find them."
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