The campaign depends on daily eight-hour ceasefires between Israel and Hamas militants in specific areas.

The complex campaign, aimed at children under 10, comes after confirmation last week that a baby had been paralysed by type 2 polio, the first such case in 25 years in the region.

WHO officials say at least 90% of children need to be vaccinated twice, with a four-week gap between doses, for the campaign to be successful. However, the campaign faces major challenges in Gaza, which has been devastated by nearly 11 months of war.

The WHO said the operation would be carried out in three phases - in central, southern and northern Gaza.

The fighting will pause for at least eight hours for three consecutive days in each phase. The ceasefires can be extended by one day in each phase, which the WHO says may be necessary.

This means each round of vaccination could take less than two weeks.

“The most important thing now is to ensure both the security and the access needed to effectively carry out the operation,” Joyce Msuya, the UN’s acting aid chief, said on Thursday.

UN Secretary-General Antonio Guterres, WHO and UNICEF on August 16 called on the fighting parties to commit to a humanitarian ceasefire to allow the vaccination campaign to take place.

About 1.2 million doses of vaccine have been delivered to Gaza ahead of the campaign, with an additional 400,000 doses on the way to the region, WHO officials said on Friday.

Cao Phong (according to Reuters)