As fighting continues in northern Gaza amid the Israel-Hamas war, international aid organizations are warning that the ongoing polio vaccination campaign has had to temporarily pause.
After the first case in 25 years was detected in the strip in August, several organizations partnered with the Hamas-run Gaza Ministry of Health with the goal of vaccinating more than 640,000 children under age 10 in two rounds.
The first round was completed in mid-September with the second round beginning in mid-October with brief humanitarian pauses to allow for inoculation. The United Nations Children's Fund (UNICEF) said its polio vaccination rounds were largely successful in central and southern Gaza.
However, intense fighting, massive displacement and lack of humanitarian access have hindered health officials' ability to distribute vaccines.
Marwan Al-Hams, director-general of field hospitals in Gaza, told ABC News on Tuesday the second phase of the polio vaccination campaign has been unable to take place in northern Gaza City and the northern Gaza Strip, with 110,000 children in need of a second dose.
The deadline to give children a second dose is mid-November, according to UNICEF. If any more time passes, immunity from the first dose will sharply drop,
"There are hundreds of people [who] have been killed over the past weeks, many more injured," Rosalia Bollen, UNICEF's communication specialist in Gaza, said. "There are hospitals that have been raided under siege. So, the conditions simply are not there, to roll out this second round in North Gaza."
The Ministry of Health warned on Wednesday warned that not continuing the campaign puts thousands of children at risk and could reverse progress made in global efforts to eradicate polio.
Israeli officials have not commented on the pause of the polio vaccination campaign.
It comes as Israel's legislative body, the Knesset, passed two bills on Monday ending the Israeli government's ties to the United Nations Relief and Works Agency (UNRWA), effectively banning the organization from working inside of Israel or with any Israeli authorities.
The first bill bans UNRWA from operating in Israel, including in east Jerusalem. The second bill prohibits any Israeli state or government agency from working with or "liaising" with UNRWA or anyone on its behalf. The bills have a three-month waiting period before they take effect, and it is expected they will be challenged in Israel's High Court.
Israel has alleged that 19 UNRWA members participated in the Oct. 7, 2023 terrorist attack in Israel. An independent investigation by the U.N.'s Office of Internal Oversight found that, in 10 cases, there was no evidence or insufficient evidence to support the staff members' involvement. In the remaining nine cases, evidence obtained suggested the staff members may have participated. UNRWA said it terminated the contracts of the nine accused staffers.
A source from the Israeli Prime Minister's Office told ABC News on Wednesday, "UNRWA is tainted with terror and perpetuates the Palestinian problem. That is why the ban is due."
UNRWA is the main U.N. agency operating within Gaza and Israel's decision drew strong condemnation from the U.N. and world leaders. UNICEF spokesman James Elder told reporters at a press conference that if UNRWA can't operate, it will lead to the collapse of the humanitarian system in Gaza.
"UNICEF would become effectively unable to distribute lifesaving supplies," he said. "Here, I'm talking vaccines, I'm talking winter clothes, I'm talking hygiene kits, health kits, water -- water and sanitation RUTF (Ready-to-Use Therapeutic Food) for malnutrition, and we know, again, we're knocking on the door of famine -- on all ranges of nutrition supplies. So, a decision such as this suddenly means that a new way has been found to kill children."
Since Hamas launched a surprise terrorist attack in Israel on Oct. 7 of last year, and Israel responded by declaring war, at least 43,163 people have been killed in Gaza and at least 101,510 have been injured, according to the Gaza Ministry of Health. More than 1,700 people in Israel have been killed and about 8,700 people have been injured, according to Israeli officials.
ABC News' Jordana Miller, Dana Savir and Sami Zyara contributed to this report.