Updated July 27, 2024 at 09:36 AM ET
When Dr. Ayadil Saparbekov was in Gaza late last week, he saw a scene that’s become familiar since the war started: Sewage overflowing in the streets. Young children jumping and splashing in it.
He cringes knowing diseases might be festering in the water. And then he got word of another concern to add to his list: Polio. The virus has turned up in the enclave’s wastewater.
For more than 25 years, the Gaza Strip has been polio free. Then last week polio was detected in six out of seven routine sewage samples.
“It's a very dangerous disease. And, in the situation of Gaza, it's beyond dangerous,” says Saparbekov, the World Health Organization’s health emergency team lead for Gaza and the West Bank.
The news sparked an international investigation. This week teams of investigators arrived in Gaza and fanned out in search of active cases of polio. They're collecting stool samples, interviewing parents and combing through medical records in search of paralysis cases, one of the most serious symptoms of the disease. They haven’t found any cases yet but infectious disease experts say it’s likely circulating silently in the population with asymptomatic and mild cases.
The investigators are also hoping to get a picture of the virus’ journey through Gaza and what to do about it “to get to the bottom of it,” Saparbekov says. “How has this happened? When did it happen? And where did it happen?”
Clues are beginning to emerge.
How? When? Where?
Saparbekov says valuable information came when the U.S. Centers for Disease Control and Prevention stepped in to do genomic sequencing. They linked the virus found in Gaza to a strain circulating in Egypt last year.
“It could have been brought by anyone including the smugglers, the truck drivers,” Saparbekov says. “And the CDC estimates that it could have been brought in as early as September 2023, even before the conflict started.”
This rough timeline is “very, very important information” according to Dr. Olakunle Alonge, director of the Sparkman Center for Global Health at the University of Alabama at Birmingham. He says it’s an indication that the virus is “likely to have spread through a lot of people,” meaning there’s a good chance it has mutated and became more virulent and, therefore, more likely to make people sick.
Alonge says when he first heard about the polio virus surfacing in Gaza’s wastewater it was “not surprising” since polio cases often map closely with war and conflict. Pointing to Nigeria, the Democratic Republic of Congo and Syria, he explains that when unrest disrupts polio vaccination programs and damages sanitation infrastructure – both of which have happened in Gaza – the stage is set for a polio outbreak.
Wild polio versus vaccine-derived polio
A close look at the sample from Gaza reveals another fact too. This is vaccine-derived polio.
As wild polio cases have dwindled, vaccine-derived polio has emerged as a growing problem in parts of the world today.
Here’s how it works: The oral polio vaccine – which is not used in the U.S. but is used in many lower income countries – contains a weakened live polio virus. This works well for the person being vaccinated. It’s weak enough so they don’t get sick but strong enough to build up lifelong immunity. The issue is that for a few weeks after swallowing a dose, the person can shed the weakened virus in feces and into the sewage. From there it can mutate, regain strength and infect someone who is unvaccinated and comes into contact with contaminated wastewater.
Raul Andino, a microbiologist at the University of California, San Francisco, set out to fix this problem. He modified the viral genome used in the vaccine to make it less likely to mutate.
This strategy worked and Andino helped create a new polio vaccine that’s “100 times safer,” he says. “It's like you were driving a 1950s car, and now you're driving a 2020 car.”
His new vaccine - the nOPV2 - was authorized for use a few years ago and has been deployed in dozens of countries. However, there’s not enough of it, and that means the old version is still being used.
“That's why the stress right now is trying to produce enough doses for everybody,” Andino says.
What now?
In Gaza, Saparbekov says investigators are busy at work trying to identify which populations are most at risk. They are also trying to rapidly reeducate health-care providers, who have likely never seen a case of polio.
“If in 25 years you don't see some disease, you may simply forget how it looks,” he says, explaining that they are reminding clinicians about the symptoms and how to store a fecal sample for testing.
Plus, Saparbekov says, he’s alerted WHO headquarters and UNICEF that they may need to quickly do a mass polio vaccination campaign with the new, safer polio vaccine.
Before the war, polio vaccination coverage in Gaza was over 95%. No longer. It’s now officially at 89%. But Saparbekov says it’s likely even lower. “There are a number of children we cannot reach. We don't know if they're alive, if they received their vaccine,” he says.
On Sunday, he will receive a report containing the investigators’ findings and their recommendation. He is bracing himself for a possible vaccination campaign and what that might mean.
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