For 25 years, there had not been a single confirmed case of polio in Gaza. But after 10 months of Israel’s war in the strip — which has devastated the health care system and created dangerous and unsanitary conditions for Palestinians — a baby became partially paralyzed last month after contracting the disease.

As the virus spread in the besieged enclave, UN Secretary-General António Guterres called for an immediate humanitarian ceasefire to allow for a mass vaccination campaign in Gaza. Since then, Israel has agreed to a series of three-day humanitarian pauses in the northern, central, and southern parts of the strip. As of Monday, the World Health Organization (WHO) said that vaccination efforts have hit their targets so far, reaching more than 161,000 children under 10.

But there is still a long way to go before health officials can declare that polio is no longer a public health threat in Gaza. To get there, WHO must reach 90 percent of children under 10, or an estimated 640,000. Each child needs to receive two rounds of vaccines, and the second round of vaccinations is set to start four weeks after the first doses are administered.

That makes the vaccination drive hard to implement, especially if the war continues between humanitarian pauses because more people will be displaced and more infrastructure will be destroyed. If Israel continues issuing evacuation orders or its attacks on infrastructure in Gaza, for example, it will be “very difficult for humanitarian actors to move around and be able to provide vaccines for not only polio but for other diseases,” said Julia Bleckner, senior health researcher at Human Rights Watch.

The nearly eradicated disease poses a serious risk for Palestinians in Gaza. And while health officials say it’s impossible to tell if polio cases will remain contained, experts warn that a broader outbreak is possible and could have consequences for the region and potentially spread beyond.

Polio, which mostly affects children under 5, is a highly infectious disease that attacks the nervous system and can quickly cause total and permanent paralysis. While there’s no cure, it can be prevented through vaccines, which is why most countries have been able to successfully eradicate the disease. In fact, since the Global Polio Eradication Initiative launched in 1988, confirmed polio cases have decreased by 99 percent around the world.

For decades, Gaza was an area where polio was considered to be eradicated. But in July, health officials detected the polio virus in wastewater samples in Khan Younis and Deir al Balah, in southern and central Gaza. ​​“Left unchecked, [the poliovirus] would have a disastrous effect not only for Palestinian children in Gaza, but also in neighboring countries and the region,” Guterres said last month.

The spread of polio in Gaza is likely the result of what are known as vaccine-derived strains of the virus. One version of the polio vaccine works by exposing people to a live but weakened form of the poliovirus. As a result, people who receive that vaccine can shed some of that weakened virus, usually in wastewater. If that virus is allowed to keep circulating through a community for long enough, it can eventually turn back into the kind of strain that can get people sick.

Overcrowded areas with poor sanitation are especially vulnerable to spreading the virus through contaminated food or water — and those are exactly the conditions Palestinians in Gaza have been living in since the war started last October, particularly since Israel has attacked water and sanitation infrastructure.

Add to that the fact that this war has significantly reduced the number of vaccinated people in Gaza. Before October 2023, 99 percent of people in the strip had been routinely immunized, but that number dropped to lower than 90 percent in the first three months of this year, according to the WHO.

That this is the first polio case in 25 years is “not a coincidence,” Bleckner said.

The most pressing concern for health officials is to ensure that 90 percent of Palestinian children under 10 are vaccinated as quickly as possible. So far, the results of the campaign have been promising: According to the WHO, the 160,000 children vaccinated in the first two days of its drive have surpassed the agency’s projection of reaching 150,000 children at this point.

But it’s unclear how sustainable that success will be given that the war is still ongoing. As humanitarian pauses lift, obstacles could emerge that could prevent health officials from meeting their targets. Last week, for example, the United Nations said that Israel’s near-constant evacuation orders have hindered their aid workers’ efforts to reach Palestinians in need.

Within Gaza, it’s also possible that health officials will run into some vaccine hesitancy — one of the reasons polio has been spreading in some parts of the world. And for some Palestinians, the fact that the vaccination campaign is coming from international organizations rather than Israel isn’t enough to alleviate their skepticism. As one Palestinian mother told Al Jazeera, “People here have lost faith in anything global or Western.”

There’s also the question of safety. “For parents trying to bring their kids to get vaccinated, how are they going to move safely to health care centers when the majority of health care centers are inaccessible at this point and barely functioning?” Bleckner said. And after Israel attacked refugee camps, schools, hospitals, and even food distribution sites, it’s understandable that some parents might have some concerns that no facility is safe.

Around the world, the spread of polio has been very limited, but it’s still considered to be endemic in Afghanistan and Pakistan. According to the Global Polio Eradication Initiative, every part of the world will remain at risk until the virus is eradicated from those countries. That’s especially true for low-income countries with inadequate public health infrastructure. In recent years, Mozambique and Malawi reported wild poliovirus cases — that is, poliovirus that is circulating naturally as opposed to the vaccine-derived strains.

For the health of Palestinians in Gaza and others in the broader region, it’s critical for the current vaccination drive to succeed. But because it’s taken so long to implement — experts have been warning Israel and the world about a potential polio outbreak for months, and Israel has been vaccinating its soldiers since July — it’s going to require an extraordinary effort.

“There’s no reason why any kid in 2024 should have polio. It’s an entirely preventable disease, so even one confirmed case — and the WHO has also identified that there are multiple kids now showing symptoms of paralysis — that’s already too late,” Bleckner said. “The conditions that people are living in in Gaza are so honestly horrific and enabling the spread of disease, it’s really a fight against time in order to stop the catastrophic spread of this disease and others.”