Stopping any polio outbreak starts with vaccine procurement, transport by airplanes and trucks, distribution involving complex logistics, and eventually the oral administration of the vaccine by drops in the mouths of every eligible child.
However, there is another, lesser known but equally important process that must also take place to halt transmission of the poliovirus. It begins with a humble stool sample – a thumb-sized smudge of poop – taken from a child with acute flaccid paralysis (AFP), then delivered to the nearest laboratory that can test the sample specifically for poliovirus.
But nowhere in Yemen is there any such lab. So the long and arduous journey of any stool sample from a Yemeni child to a receiving lab can take up to several days – following an easterly route, to the neighboring country of Oman.
An explanation of how stool samples are transported over such a distance starts with why: monitoring children under 15 years of age for signs of AFP, which is the most common sign of poliovirus infection. The Global Polio Eradication Initiative has set a benchmark of at least three AFP cases per 100,000 children under 15 years of age, a standard that Yemen has consistently met, thanks to the effectiveness of its surveillance system. This achievement is all the more remarkable considering that Yemen is entering its ninth year of internal conflict, with resulting population displacements, widespread food and fuel shortages, and a devastated health system (in which only 46% of hospitals and health facilities are only partially functioning or completely out of service).
The second critical area of effective AFP surveillance is around the adequacy of stool samples – meaning the number of samples collected from children with AFP that reach the lab in appropriate condition for testing. If samples are in good condition, they can be tested for poliovirus and generate an accurate result, which enables Yemen’s polio programme to detect and respond to the circulation of poliovirus, ultimately preventing more children from becoming infected.
Meticulously collected data consistently tells us that the vast majority of stool samples are reaching the lab at the right temperature, and in good condition for testing. But what's left unexplained is the arduous journey that every sample has made to reach its final destination.
Each journey starts in the same way: a health worker coming across a child with AFP. Every health worker must then notify a surveillance focal point who immediately reaches out to the child’s family to coordinate stool sample collection. Time is of the essence: the sooner a sample is collected after the onset of paralysis, the more reliable the results.
Photo: A surveillance coordinator handles stool samples in the field.
Dr Mohammed Sharafulddin, AFP surveillance coordinator in Al Mahaweet governorate, typically handles collection in his area. He begins by loading a cool box with ice packs before embarking on travels that often take him into and through some of Yemen's highest mountains that can peak at more than 3,000 meters (nearly two miles) above sea level.
“Eight of the nine districts we cover are extremely difficult to access, and I drive an old, beat-up car. I travel different roads as far as I can go, and from there I must continue by donkey or by foot," explains Dr Sharafulddin.
“It may seem like simple work to collect two samples from people's homes at least 24-48 hours apart. But it is actually a very complex task to do this while maintaining their right temperature until they are delivered to the Ministry of Public Health and Population in Sana’a,” he adds.
All stool samples collected from all districts and governorates in Yemen are sent to the central lab at the MoPHP in Sana’a, where they are placed in refrigeration units and continuously temperature-monitored via attached tags. Every two or so weeks – by which time the stool samples usually number between 80 and 100 – they are sent together in one large batch to the WHO warehouse in Sana’a. From there they are dispatched via a single private courier service to the Regional Reference Lab in Muscat, Oman. Drives to the border typically take up to four or five days, sometimes as long as a week or even 10 days. Long waits at numerous checkpoints in blistering heat, further time needed to traverse frontlines of fighting, slow crawls along damaged roads, and unplanned encounters with other delays if not hazards – all can be part of a single trip. There are additional days of travel on the other side.
Since 2021, thousands of stool samples have been sent to the National Polio Lab (NPL) in Muscat: 2,648 samples in 2022 (two samples each from 1,324 children), and 174 samples already in the first two months of 2023 (two samples each from 87 children). This WHO-accredited lab has been a lifeline for the polio programme during multiple outbreaks of circulating variant polioviruses in Yemen – thanks to targeted funding from the Government of Japan.
To understand the impact of this funding, it helps to consider the urgency of getting samples to the lab: the longer it takes to get a result, the more time the virus has had to infect children and expand its area of circulation. Thanks to the Government of Japan, the amount of time the average sample spends on the road has been cut from four weeks to three.
Photo: A focal point at the MoPHP receives stool samples receiving from the epidemiological coordinator.
Upon reaching the RRL, all samples are checked closely and data from the refrigerated units' tags is downloaded to ensure the reverse cold chain has been maintained – meaning that the samples have been stored at between 2 and 8 degrees Celsius throughout their journey from being first collected in the field. If for even a single moment the cold chain has been broken, the samples cannot give a reliable result.
Once accepted by the lab, each stool sample undergoes testing to determine whether the corresponding child has been infected with poliovirus, and if so, by what variant. Here, too, the Government of Japan grant has helped shave the amount of time between detection of an AFP case and response to a polio diagnosis, cutting it down from 31 days to sometimes as few as 21.
For Dr Yasser Al Jomaie, a AFP surveillance coordinator in Amran governorate, there is no question whether the costs of these very long and difficult journeys – all the time, efforts and money spent – are worth it.
He recalls the 2009 declaration that Yemen was polio-free, and the years following when the country maintained consistently high immunization levels and kept vaccine-preventable diseases at bay.
"Poliovirus resurfacing in Yemen, and our difficulties in containing it, is a relapse of years of epidemiological efforts,” Dr Al Jomaie explains.
“The core of what we do in epidemiology is to mitigate the risks of disease outbreaks and to protect the community – especially children. Vaccination rates are low in many areas, and the risks are high. I consider investigation and surveillance work to be critical to the health situation in Yemen right now,” adds Dr Al Jomaie.
For the families who receive surveillance workers like Dr Sharafulddin and Dr Al Jomaie, and then wait for a diagnosis of polio, the result of getting their child’s stool samples to Oman is negligible: while the diagnosis can explain their child’s condition, it doesn’t change it.
But the surveillance network can be life-changing for other children and their families, as Dr Al Jomaie explains. Stool samples testing positive for poliovirus immediately trigger a case investigation, the collection of further contact samples and, if so required and wherever possible, a vaccination response. If any child in Yemen has contracted poliovirus, a positive result from the Muscat lab can be the development that protects that child’s community, children in nearby communities, and even children in neighbouring countries from contracting the same disease, by ensuring that those children are vaccinated against polio as quickly as possible.
“Low immunization rates and vaccine hesitancy are placing the children of Yemen at high risk of disease outbreaks – especially polio. And what is heartbreaking about polio is that it brings lifelong suffering caused by permanent disability. There is no going back,” says Dr Al Jomaie. “We provide epidemiological proof of the situation and timely response…we are the eyes and ears of the polio programme on the ground.”
Story:© WHO/ Hanan Eshaq & Kevin Cook
Photos: © WHO/ Omar Nasr/ Field Coordinators