A first group of babies received polio vaccinations in Gaza on Saturday ahead of the official start of a much-anticipated United Nations-led campaign on Sunday.

Babies in the Nasser Hospital in Khan Younis, central Gaza, were among the first to receive the vital vaccines on Saturday, according to footage filmed by news agency Reuters.

The main UN agency in Gaza, UNRWA, plans to immunize over 640,000 children in the war-torn enclave, facilitated by a series of pauses in fighting agreed to by Israel.

During a press conference organized by the Ministry of Health in Gaza to officially launch the campaign, Deputy Health Minister Yousef Abu Al-Reesh said that if “the international community wants the campaign to succeed,” it should call for a permanent ceasefire in Gaza.

The return of polio to Gaza is a measure of the destruction wrought by more than 10 months of Israeli bombardment. The UN’s campaign comes after the highly infectious virus was found in sewage samples in the strip in June. A baby has since become the first person in Gaza in 25 years to be diagnosed with polio.

Before the war, Gaza had near-universal polio vaccine coverage, but it has since dropped below 90%. Polio mostly affects children under 5 years old, and can cause irreversible paralysis and even death. It’s highly infectious and there is no cure. It can only be prevented by immunization, according to the World Health Organization.

The vaccination drive comes as aid agencies reported Israeli attacks on their convoys. One charity said an Israeli strike on a humanitarian vehicle in Gaza killed several employees of a transportation company. The Israeli military said it targeted “armed men” who had taken over the convoy.