What We Know About the Polio Crisis in Gaza

A mass polio vaccination campaign for young children will begin in the Gaza Strip on Sunday, an especially challenging effort in a war zone where hundreds of thousands of people have been displaced repeatedly, buildings and infrastructure have been destroyed and moving around is often dangerous for aid workers and civilians.

The inoculation campaign depends on brief pauses in fighting and requires coordination among Israeli authorities, humanitarian agencies, aid workers and the health ministry in Gaza, which is run by Hamas.

Israel and Hamas have both said they will abide by staggered pauses in fighting to allow aid workers to vaccinate children, and Israel has said it will not issue evacuation orders in places where vaccinations are happening.

But after nearly a year of almost nonstop fighting in the enclave, there are fears the agreement may not hold long enough to complete the two rounds of vaccinations that health authorities say are needed to prevent the spread of the disease in Gaza and beyond.

“We welcome the commitment to humanitarian pauses in specific areas, and suspension of evacuation orders for the implementation of the campaign,” Tedros Adhanom Ghebreyesus, the director general of the World Health Organization, said in a post on social media on Thursday. “But the only lasting medicine is peace. The only way to fully protect all the children of Gaza is a cease-fire.”

Why is there polio in Gaza?

There are two basic, highly effective types of polio vaccine: an injection that uses dead virus, and an oral inoculation that uses a significantly weakened live strain of the virus.

Wealthier countries now use only the injected vaccine, but the oral version, cheaper and easier to transport and administer, is still commonplace in poorer regions of the world.

The oral vaccine carries a small risk because a vaccinated person can shed live virus in stool or body secretions. That weakened virus poses little threat on its own, but where sanitation is poor and vaccination rates are not high enough, the weakened strain can infect more people and, more troubling, can eventually mutate into a dangerous form.

The widely used vaccines given to young children formerly protected against all three types of poliovirus. But several years ago, with naturally occurring Type 2 eradicated, health authorities removed it from oral vaccines given routinely around the world, including in Gaza.

Health experts say that decision has backfired, creating a population of children who could be susceptible to that type.

Sure enough, the poliovirus detected in Gaza is believed to be vaccine-derived Type 2, which has also caused outbreaks in Africa in recent years. The vaccines to be delivered in Gaza are oral doses specifically targeting Type 2 poliovirus.

Polio vaccination rates in Gaza were at about 99 percent in 2022 but have dropped significantly among babies because of the war, in addition to the vulnerability to Type 2 for vaccinated children. At least 90 percent of children under 10 need to be vaccinated to stop the disease from spreading, Dr. Rik Peeperkorn, the top W.H.O. representative in Gaza, told reporters on Thursday.

How widespread is polio in the Gaza Strip?

The first confirmed polio patient in Gaza in 25 years is a boy named Abdul Rahman Abu Al-Jidyan, who is almost a year old and living with his family in a tent in Deir al Balah, in central Gaza. He was born just before the war, and was unable to get routine vaccinations because the family was constantly forced to move, his mother said.

About two months ago, he stopped crawling and was feverish. His family took him to a hospital, which sent a sample to a lab in Jordan. A test confirmed health officials’ fears: He had polio.

Gazan health officials have reported multiple children with symptoms consistent with polio, most likely the result of what UNICEF and W.H.O. officials said were severely unsanitary conditions and deteriorating health services.

Poliovirus has been detected in wastewater samples in Khan Younis, in southern Gaza, and Deir al Balah, both of which have large populations of displaced Palestinians who have fled Israeli airstrikes.

How will the vaccination campaign work?

Israel has agreed to staggered pauses in military operations, starting Sunday. Vaccinations will begin in central Gaza and last for three days there, with the option for an extension if necessary. The humanitarian pauses will last from early morning until afternoon.

Health authorities plan to next move to southern Gaza for several days, and then the northern region of the enclave.

The World Health Organization and UNICEF, the U.N. children’s fund, have delivered more than 1.2 million doses of polio vaccines to distribute to about 640,000 children in Gaza under 10 years old. Another 400,000 doses are on their way.

About 2,100 health and community aid workers in Gaza, at some 700 medical facilities, mobile clinics and shelters, will be administering the vaccines. After they complete the first round, a second, booster round of immunizations will need to be given four weeks after the first dosages. Israel has agreed to staggered pauses for boosters, too.

What is the risk if this campaign fails?

Spread beyond Gaza remains possible for however long the virus continues circulating, underscoring the immediate need for the vaccination campaign. “It is urgent; it is vital,” Antony J. Blinken, the secretary of state, told reporters this month in Tel Aviv after he met with Israeli officials.

A decades-long global campaign has reduced polio cases by more than 99 percent worldwide. Wild-type poliovirus is now known to exist only in two strongholds — Pakistan and Afghanistan.

Truly eliminating the disease globally would require eradicating wild-type polio in those places and phasing out the live-virus component in oral vaccines. For now, the best protection against polio for any community is still vaccine-induced “herd immunity,” according to Oliver Rosenbauer, a spokesman for the Global Polio Eradication Initiative.

In places where almost all children have been vaccinated, the likelihood of spread is minimal. But a person anywhere who is unvaccinated remains at risk, as evidenced by a 2022 outbreak that reached New York.

“As long as polio is anywhere,” Mr. Rosenbauer said, “all countries are at risk.”