Successive Israeli evacuation orders in Gaza have displaced 90 percent of its 2.1 million residents since the Israel-Hamas war began in October, the top UN humanitarian official for Palestinian territory says.

US Vice President Kamala Harris says she and President Joe Biden are working to end the war in Gaza, where the International Rescue Committee says the polio virus has been circulating for the first time in a quarter-century because of the destruction of hospitals and water infrastructure, along with overcrowded living conditions.

White House national security spokesman John Kirby said Friday that cease-fire talks in Cairo have been constructive and will continue over the weekend. The United States, Egypt and Qatar are mediating the talks. A crucial sticking point involves Israel’s demand for lasting control over two strategic corridors in Gaza.

The war began on Oct. 7, when Hamas and other militants stormed Israel, killed around 1,200 people — mostly civilians — and abducted around 250. About 110 hostages are still inside Gaza, a third of whom are believed to be dead. The Israeli offensive launched in response has killed more than 40,000 Palestinians in Gaza, according to the local Health Ministry, which doesn't say how many militants or civilians were.

The United Nations is stepping up its demand for humanitarian pauses in fighting in Gaza to vaccinate more than 600,000 children against polio following the World Health Organization’s confirmation that a 10-month-old unvaccinated baby has polio and is partly paralyzed.

It is the first internationally confirmed polio case in Gaza in 25 years. WHO Director-General Dr. Tedros Adhanom Ghebreyesus said in a social media post Friday that the baby in central Deir al-Balah developed paralysis in the lower left leg. Gaza’s Ministry of Health previously confirmed the case.

WHO and the U.N. children’s agency UNICEF are working with the Gaza ministry to implement two rounds of polio vaccination, four weeks apart, the U.N. humanitarian office said.

The key is agreement for humanitarian pauses from Israel, Hamas and other militants in Gaza. U.N. spokesman Stephane Dujarric said “those discussions are continuing.” He said a number of refrigerated trucks to keep the vaccines cold have arrived in Gaza, but the vaccines haven’t been delivered yet.

The U.N. Office for the Coordination of Humanitarian Affairs also reported that three Israeli evacuation orders on Wednesday and Thursday affected 15 neighborhoods in Deir al-Balah and southern Khan Younis and included nearly 150 sites where displaced Palestinians had sought shelter.