The vaccine drive has been more successful than expected, a W.H.O. official says.

How many hostages are still in Gaza?

More than 60 living hostages, and the bodies of about 35 others taken captive on Oct. 7 but believed to be dead, are still in Gaza, according to the Israeli authorities.

In all, about 250 people were abducted on Oct. 7, according to Israeli officials, who include in that number 37 people who were murdered in the initial attack and whose bodies were taken back to Gaza. Those taken were mainly civilians but also included military and security personnel. They were men, women and children, Israeli citizens as well as people who were citizens of the United States, Britain, France, Russia, Germany, Mexico, Thailand and other countries.

How many hostages are Americans?

In all, 12 people with U.S. citizenship were abducted to Gaza on Oct. 7, according to the Israeli government. Two of them, Judith Raanan and her daughter, Natalie Raanan, were freed on Oct. 20 after pressure on Hamas by the United States and Qatar. Two others were released during a cease-fire in November.

One of the hostages, Hersh Goldberg-Polin, 23, a dual Israeli American citizen, was among the six who were found dead in Gaza over the weekend. He had been taken from a music festival in southern Israel on Oct. 7.

The American Jewish Committee, an advocacy organization for Jewish people around the world, on Saturday listed four American citizens who were still being held alive in Gaza. They are Edan Alexander, 20; Sagui Dekel-Chen, 35; Omer Neutra, 22; and Keith Siegel, 64. Three others are presumed dead: Itay Chen, 19; Gadi Haggai, 73; and Judi Weinstein Haggai, 70.

How many hostages have been freed?

Since Oct. 7, 117 people have been released, according to the Israeli authorities. More than 100 were freed during a one-week cease-fire at the end of November in exchange for 240 Palestinians held in Israeli detention.

In addition, eight people have been freed during Israeli military operations. Last week, a Bedouin Arab citizen of Israel was rescued after Israeli commandos found him alone in a tunnel in southern Gaza.

In the most high-profile hostage rescue, in June, soldiers and special operations police rescued four hostages from buildings in the town of Nuseirat, in central Gaza. Scores of Palestinians, including women and children, were killed during that operation, according to the health ministry in Gaza.

In December, Israeli forces mistakenly killed three hostages who had escaped from their captors and were attempting to approach them. The army said the shooting violated its rules of engagement.

What are the conditions like for those still in captivity?

Hostages who have returned from captivity in Gaza have shed some light on where they were held and what the conditions were like. Some were held in hospitals, others in apartments, a mosque and even a destroyed supermarket. Hamas has also been known to hold hostages underground in a network of tunnels. The Israeli military said on Sunday that the bodies of the six slain hostages were found in a tunnel.

Many hostages who have left Gaza have described being moved repeatedly during their captivity, under heavily armed guard. They reported being subjected to physical and psychological abuse.

Andrey Kozlov, 27, a Russian Israeli, provided a detailed account of his time in captivity after he was rescued by the Israeli military in June. He described being held in six locations in the first two months and being moved to an apartment in mid-December. In some places, he and the hostages he was held with had only a pail for a toilet, and food was scarce.

After the rescue of Mr. Kozlov and three other captives, Dr. Itai Pessach, the head of a medical team for returning hostages, said they were malnourished. “They were all abused, punished and tortured physically and psychologically in many ways,” he said.

Gabby Sobelman contributed reporting.