The UN health agency and its partners are launching a campaign from Sunday to vaccinate 640,000 Palestinian children in Gaza against polioan ambitious effort amid a war that has devastated the enclave’s healthcare system.

The campaign comes after the first case was reported of polio in Gaza after 25 years – a 10-month-old boy, which caused the paralysis of one of his legs. The World Health Organization says the presence of one case suggests there may be hundreds of others who are infected but not showing symptoms.

Most people with polio have no symptoms, and those who do get sick recover in about a week. But there is no cure, and when polio causes paralysis it is usually permanent. If the paralysis affects the respiratory muscles, the disease can be fatal.

The vaccination effort will not be easy: Gaza’s roads have been largely destroyed, its hospitals badly damaged and its population sheltered in isolated enclaves.

The WHO said on Thursday it had reached an agreement with Israel for limited ceasefires to allow the vaccination campaign to take place. Even so, such a large-scale campaign will face great difficulties in an area covered in rubble, where 90% of Palestinians are displaced.

How long will it take?

The three-day vaccination campaign in central Gaza will begin on Sunday, during a “humanitarian pause” that will last from 6 a.m. to 3 p.m., said Dr. Rick Reperkorn, WHO Representative in the Palestinian Territories.

In coordination with Israeli authorities, vaccinations will also take place in southern and northern Gaza during similar pauses, he added during a video conference from Deir al-Balah in central Gaza.

Who will make the vaccine?

The vaccination campaign targets 640,000 children under the age of 10, according to the WHO. Each child will receive two drops of oral polio vaccine in two doses, the second dose given four weeks after the first.

Where will the vaccinations be given?

Vaccination sites span Gaza, both inside and outside the Israeli evacuation zones, from Rafah in the south to the northern areas of the territory.

The Ramallah-based Ministry of Health said on Friday there would be more than 400 “permanent” vaccination sites, most in Khan Younis, where the population density is highest and home to 239,300 children under 10. Fixed facilities include health centers, hospitals, clinics and field hospitals.

Elsewhere in the territory, there will also be about 230 sites where the vaccines will be distributed.

Where are the vaccines kept now?

About 1.3 million doses of the vaccine traveled through the Kerem Shalom checkpoint and are currently being stored in “cold conditions” at a warehouse in Deir al-Balah. This means that the warehouse is able to maintain the correct temperature so that the vaccines are not damaged.

Another shipment of 400,000 doses is due to be delivered to Gaza soon.

Vaccines will be transported to distribution sites by a team of more than 2,000 volunteer doctors, said Ammar Ammar, a UNICEF spokesman.

What are the challenges?

Organizing any kind of campaign that requires crossing the Gaza Strip and interacting with its medical system is bound to create difficulties.

The UN estimates that around 65% of the total road network in Gaza has been damaged. Nineteen of the strip’s 36 hospitals are out of business.

The northern part of the territory is cut off from the south, and movement between the two areas was difficult throughout the war due to Israeli military operations. Aid groups were forced to suspend their movements due to security concerns after convoys were targeted by the Israeli army.

Peppercorn said Friday that the WHO cannot do house-to-house vaccinations in Gaza, as it has done in other polio campaigns. When asked about the sustainability of the effort, he emphasized that the WHO believes that “it is possible if all the pieces of the puzzle are in place. “

How many doses do children need and what happens if one is missed?
The World Health Organization says that children usually need about three to four doses of oral polio vaccine — two drops per dose — to be protected against polio. If they don’t get all the doses, they are vulnerable to infection.

Doctors have previously found that children who are malnourished or have other illnesses may need more than 10 doses of the polio vaccine to be fully protected.

Are there side effects?

Yes, but they are very rare.

Billions of doses of the oral polio vaccine have been given to children worldwide, and it is safe and effective. But in about 1 in 2.7 million doses, the live virus in the vaccine can paralyze the child receiving the drops.

How the polio outbreak in Gaza started

The polio virus that triggered this latest outbreak is a mutated virus from an oral polio vaccine. The oral polio vaccine contains weakened live virus, and in very rare cases, this virus is shed by those who are vaccinated and can evolve into a new form capable of starting new epidemics.