Investigators search for polio cases in Gaza after polio found in sewage : NPR

Palestinian children sit in a sewage-filled street in Deir el-Bala, in the central Gaza Strip, on July 23. Polio was detected in sewage samples in the Gaza Strip a week ago, and infectious disease experts now suspect there may already be mild cases among residents.

Majidi Fathi // NurPhoto via Getty Images

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Majidi Fathi // NurPhoto via Getty Images

When Dr. Ayadil Saparbekov visited Gaza last weekend, he saw a scene he's become familiar with since the war began: streets filled with sewage, with young children jumping and splashing in it.

The possibility of disease in the water frightened him, and adding to his concerns was news that polio was a virus that had been detected in the exclave's wastewater.

The Gaza Strip has been polio-free for more than 25 years, but last week the virus was detected in six of seven routine sewage samples.

“This is a very dangerous disease, and in the Gaza situation it's past dangerous,” said Saparbekov, head of the World Health Organization's health emergency team for the Gaza Strip and the West Bank.

The news has sparked an international investigation. Investigative teams arrived in Gaza this week to begin searching for active cases of polio. They're taking stool samples, interviewing parents and combing medical records, looking for cases of paralysis, one of the disease's most serious symptoms. No cases have been found yet, but infectious disease experts say it's likely asymptomatic or mild cases are spreading silently among the population.

Investigators also want to understand the virus's path through Gaza and what to do about it, “to get to the bottom of it,” Saparbekov said. “How did this happen? When did it happen? Where did it happen?”

Clues are beginning to emerge.

How? When? Where?

Saparbekov said the US Centers for Disease Control and Prevention gained valuable information when they stepped in with genome sequencing, linking the virus found in Gaza to a strain circulating in Egypt last year.

“It could have been brought in by anyone, including smugglers or truck drivers,” Saparbekov said. “The CDC estimates it could have been brought in as early as September 2023, before the conflict began.”

This rough timeline is “very important information,” according to Dr. Olakunle Alonge, director of the Sparkman Center for Global Health at the University of Alabama at Birmingham. He said it indicates the virus “likely has spread to a lot of people,” meaning it's likely mutated to become more virulent and therefore more likely to make people sick.

When Alonge first heard that the poliovirus had surfaced in Gaza's wastewater, he said it “was not a surprise” because polio cases often go hand in hand with war and conflict. Citing Nigeria, the Democratic Republic of Congo and Syria as examples, he explained that when unrest disrupts polio vaccination programs and undermines sanitation infrastructure (as has happened in Gaza), it sets the stage for a polio outbreak.

Wild polio vs vaccine-derived polio

A closer look at the Gaza samples revealed another fact: Vaccine-derived polio.

As wild polio cases decline, vaccine-derived polio has emerged as a growing problem in parts of the world today.

Here's how it works: The oral polio vaccine (not used in the U.S., but in many low-income countries) contains a weakened, live poliovirus that's effective for people who get vaccinated — weakened enough that it doesn't make them sick, but strong enough to build lifelong immunity. The problem is that for a few weeks after you get the vaccine, the weakened virus can be shed in your feces or sewage. From there, the virus mutates and regains strength, and can infect unvaccinated people if they come into contact with contaminated sewage.

Raul Andino, a microbiologist at the University of California, San Francisco, set out to solve this problem: he modified the genome of the virus used in the vaccine to make it less likely to mutate.

The strategy worked, and Andino said it helped develop a new polio vaccine that was “100 times safer. It's like driving a car from the 1950s and now you're driving a car from 2020.”

his New vaccine “nOPV2” approved It was launched several years ago and has been adopted by dozens of countries, but there are not enough of them and older versions are still in use.

“That's why there's stress right now about producing enough vaccine for everyone,” Andino said.

What next?

In Gaza, Saparbekov said assessors were busy working to identify which groups were most at risk, and also trying to quickly retrain health workers who likely had never seen a polio case.

“If you go 25 years without knowing you have a disease, you may forget what the symptoms were,” he said, explaining that he reminds clinicians of symptoms and how to preserve stool samples for testing.

Saparbekov also warned WHO headquarters and UNICEF that there may be an urgent need to launch a large-scale polio vaccination campaign using a new, safer polio vaccine.

Before the war, Gaza's polio vaccination rate was over 95 percent. That's not the case anymore. It's now officially at 89 percent, but Saparbekov says it's probably even lower. “There are so many children we can't help. We don't know if they're alive or if they were vaccinated,” he says.

He is due to receive the inspectors' report on their findings and recommendations on Sunday as he prepares for the possibility of a vaccination campaign being rolled out and what that might mean.

“My first thought was, 'Okay, how do we do this in a war zone?'” he said. “This is a monumental task ahead of us.”