The World Health Organization (WHO) and its partners are launching a vaccination campaign on Sunday to protect 640,000 Palestinian children in Gaza against polio. This ambitious effort comes amidst a devastating war that has severely damaged Gaza’s healthcare system.

The campaign was prompted by the first polio case reported in Gaza in 25 years – a 10-month-old boy, now paralyzed in the leg. The WHO states that the presence of a paralysis case suggests hundreds more children might be infected but not showing symptoms.

While most people infected with polio don’t experience symptoms, and those who do typically recover within a week, there is no cure for the disease. Polio-induced paralysis is usually permanent, and if it affects breathing muscles, it can be fatal.

The vaccination effort faces significant challenges due to the extensive damage to Gaza’s infrastructure, including roads and hospitals, and the displacement of its population.

WHO secured an agreement with Israel for limited pauses in the fighting to facilitate the vaccination campaign. Despite this, the campaign remains a monumental undertaking in a war-torn territory where 90% of Palestinians are displaced.

The three-day vaccination campaign in central Gaza will begin on Sunday during a “humanitarian pause” lasting from 6 a.m. until 3 p.m. An additional day can be added if necessary, according to Dr. Rik Peeperkorn, WHO’s representative in the Palestinian territories.

In coordination with Israeli authorities, the effort will then move to southern Gaza and northern Gaza during similar pauses, Dr. Peeperkorn explained during a video news conference from Deir al-Balah in central Gaza.

The vaccination campaign targets 640,000 children under 10, as per WHO. Each child will receive two drops of oral polio vaccine in two rounds, with the second dose administered four weeks after the first.

Vaccination sites are spread across Gaza, both inside and outside Israeli evacuation zones, from Rafah in the south to the northern reaches of the territory.

The Ramallah-based Health Ministry announced on Friday that there would be over 400 “fixed” vaccination sites – the most in Khan Younis, where the population density is the highest and there are 239,300 children under 10. Fixed sites include healthcare centers, hospitals, clinics, and field hospitals.

Throughout the territory, there will also be around 230 “outreach” sites – community gathering points that are not traditional medical centers – where vaccines will be distributed.

Approximately 1.3 million doses of the vaccine arrived via the Kerem Shalom checkpoint and are currently stored in a “cold-chain storage” warehouse in Deir al-Balah. This ensures the vaccines maintain the correct temperature and potency.

Another shipment of 400,000 doses is scheduled to be delivered to Gaza shortly.

A team of over 2,000 medical volunteers will transport the vaccines to distribution sites, according to Ammar Ammar, a UNICEF spokesperson.

The logistical challenges of conducting any campaign requiring traversal of the Gaza Strip and interaction with its medical system are substantial.

The U.N. estimates that approximately 65% of Gaza’s total road network has been damaged. Nineteen of the strip’s 36 hospitals are out of service.

The north of the territory is isolated from the south, and travel between the two areas has been difficult throughout the war due to security concerns. Aid groups have suspended trips due to concerns after convoys were targeted by the Israeli military.

Dr. Peeperkorn said on Friday that WHO cannot conduct house-to-house vaccinations in Gaza, as they have done in other polio campaigns. Addressing the campaign’s feasibility, Dr. Peeperkorn stated that WHO believes “it is feasible if all the pieces of the puzzle are in place.”

The World Health Organization states that children typically require three to four doses of oral polio vaccine – two drops per dose – to be protected against polio. Those who don’t receive all the doses are vulnerable to infection.

Doctors have previously observed that malnourished children or those with other illnesses may require more than 10 doses of oral polio vaccine to achieve full protection.

Yes, but they are very rare.

Billions of doses of oral polio vaccine have been administered to children worldwide, and it is considered safe and effective. However, in about 1 in 2.7 million doses, the live virus in the vaccine can paralyze the child who receives the drops.

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 extremely rare instances, this virus is shed by those who are vaccinated and can evolve into a new form capable of initiating new epidemics.