Why Relief Agencies Are Rushing Polio Vaccines to Gaza

In July, health officials made an unsettling discovery in Gaza: Poliovirus, a global scourge, was found in samples of wastewater. This month, the news got worse. A 10-month-old baby contracted polio and is now paralyzed in one leg.

It’s the first confirmed case of polio in Gaza in 25 years. Now international agencies are sending more than 1.6 million doses of oral poliovirus vaccine to the conflict zone in an ambitious effort to immunize 640,000 children under age 10.

Israel has agreed to three pauses in military operations, starting Sunday, to facilitate the campaign.

Health officials had been warning for months that the conflict in Gaza could eventually give way to major regressions in infectious diseases. Transmission of poliovirus — which attacks the nervous system and can lead to spinal and respiratory paralysis, and in some cases death — may already be widespread, some experts fear.

Here’s what you should know.

How could there be polio in Gaza?

Of the three naturally occurring “wild-type” viruses, only Type 1 remains; Type 2 and Type 3 have been eradicated.

But there is another form to worry about: so-called vaccine-derived poliovirus. This form now accounts for most outbreaks worldwide.

Since 2000, the United States and most wealthy countries have used an injected vaccine that does not contain live virus. But many low-income countries still rely on oral vaccines that contain live, weakened poliovirus, designed to induce an immune response without causing serious illness.

But a child receiving an oral vaccine may shed the weakened virus in stool or bodily secretions. That virus may not be as harmful as wild-type poliovirus — at first.

When vaccination rates in a population are inadequate, a vaccine-derived poliovirus may spread widely without interruption, undergoing genetic changes and eventually reverting to a type able to cause paralysis and outbreaks.

How has the conflict contributed?

Polio vaccine coverage rates in Gaza were at about 99 percent in 2022 but have dropped dramatically. The baby who was infected was unvaccinated.

At the same time, the majority of Gaza’s 2.2 million people have fled their homes for makeshift shelters, where a lack of clean water and sanitation infrastructure, plus overcrowding, make the territory ripe for the spread of disease.

In many communities, untreated sewage is flowing openly near temporary dwellings. Illnesses passed through contaminated food or water, or close person-to-person contact, are a major threat.

Airstrikes and ground combat have decimated many of the territory’s hospitals and clinics, and fewer than half of its facilities remain even partly operational. As a result, existing health infrastructure is dedicated largely to people suffering from war injuries, not to public hygiene and disease prevention.

In the midst of the crisis, disease is surging. There have been at least 500,000 cases of diarrhea and nearly one million acute respiratory infections. The W.H.O. has reported 100,000 cases of lice and scabies, and about the same number of cases of acute jaundice syndrome, or suspected hepatitis A.

What’s the plan in Gaza?

In an effort to curb a potential outbreak, global health officials have started an urgent campaign to deliver vaccines to hundreds of thousands of Palestinian children. The effort is expected to begin on Sunday.

The oral vaccines on the way to Gaza target Type 2 poliovirus, according to the W.H.O., and the campaign will involve 708 teams and 2,700 health workers.

Poor sanitation in Gaza means that at least 95 percent of children will need to receive two vaccine doses to reduce the chances that polio will re-emerge in the region, according to UNICEF.

Israel’s defense ministry said the vaccine drive would occur during three humanitarian pauses.

What does this mean for the global effort to eradicate polio?

The short answer: No one knows.

The poliovirus found in Gaza did not emerge there — it was imported somehow, perhaps from Egypt. Spread beyond Gaza remains possible for however long the virus continues circulating; it is impossible to say whether cases can be contained in Gaza.

More than 30 years ago, the World Health Assembly passed a resolution to eradicate polio, which led to mass vaccination campaigns that brought cases down by more than 99 percent worldwide. Wild-type poliovirus is now known to exist only in two strongholds — Pakistan and Afghanistan.

But Oliver Rosenbauer, a spokesman for the Global Polio Eradication Initiative, said that truly eliminating the disease would require a “one-two punch”: eradicating wild-type polio from those places, and phasing out the live-virus component in oral vaccines.

For now, the best protection against polio in any community is still vaccine-induced “herd immunity.” In places where almost all children have been vaccinated, the likelihood of spread is minimal. But a child 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.”