Bilar Shbair reported from Khan Younis in the Gaza Strip, and Erika Solomon from Berlin.

Health workers on Sunday were set to begin a polio vaccination drive in Gaza aimed at preventing an outbreak of the quick-spreading disease -- a daunting challenge in a besieged enclave shattered by 10 months of war and dependent on commitments by the war's combatants, Israel and Hamas, to abide by pledged "humanitarian pauses."

Israel, facing international pressure to prevent a wider outbreak of the crippling disease, moved with relative speed to allow agencies of the United Nations, supported by local health officials, to tackle the crisis in Gaza, where it launched a war in response to a Hamas-led attack on Oct. 7.

Although the official start of the vaccination drive was set for early Sunday morning, Gazan health authorities began the campaign on Saturday at the Nasser Hospital in the southern city of Khan Younis, according to Palestinian news media reports. Videos showed doctors and health workers squeezing droplets of the poliovirus vaccine into the mouths of children who were being treated at the hospital.

"I knew about this campaign by chance. I was frightened when I heard the word polio," said Maysaa Abu Daqqa, a mother of a 9-year-old, Habib Nizam. Ms. Abu Daqaa was waiting in a patients' room at Nasser hospital. "When I saw other women accepting the vaccinations for their children, I was encouraged to follow them," she said.

Both Hamas and Israel have agreed to the pauses in the fighting to allow the vaccinations to take place, but the campaign will be tricky to execute. With much of Gaza's infrastructure destroyed, and some 90 percent of the enclave's roughly two million residents having repeatedly fled Israeli bombardment, it may be impossible to ensure the immunization of all of the enclave's estimated 640,000 children under age 10.

For families seeking to get their children vaccinated, the challenges are layered and fraught: Not only must they trust that the cessations in fighting will hold, but many will have to navigate blocked and broken roads and expose themselves to danger and widespread lawlessness to reach the sites where vaccinations take place.