World Health Organisation, (WHO), on Tuesday, said over 161,000 children have been given the first vaccine dose against polio virus in central Gaza.
WHO said the vaccine was the first launch of UN-led mass vaccination campaign in the embattled Palestinian territory.
The number of children reached in central Gaza during the first two days of the campaign launched on Sunday exceeded expectations, with the WHO initially hoping to reach 156,000 in that period.
However, more children than expected were currently living in central Gaza, as many are constantly being displaced amid the fighting, the WHO said.
Thousands of Gazans are repeatedly forced to relocate as Israel continues to target Palestinian militant group Hamas across the Gaza Strip after almost 11 months of war.
Due to the volatile situation in Gaza, it was difficult to ensure that all children are reached by the vaccination campaign, the WHO said.
The organisations also announced that efforts in central Gaza, originally set to last three days, would likely be extended by an additional day.
The UN pressed for the start of a Gaza-wide polio campaign after the first case of polio was recorded in the territory after 25 years.
Experts fear that an outbreak might be imminent as hundreds of thousands of internally displaced people are currently forced to live in cramped living conditions.
Israel and Hamas have agreed to limited daily pauses in fighting from 6 am to 2 pm (0300 – 1100 GMT) to allow for the campaign to go ahead, though there were reports of overnight Israeli military strikes on Monday.
According to the UN, it was too dangerous for some families to go to the vaccination centres, and it was also difficult for mobile vaccination teams to reach these families due to the violence.
Following efforts in central Gaza, vaccination teams are set to inoculate some 340,000 children under the age of 10 against the type 2 polio virus in southern Gaza.
This would follow a three-day campaign targeting another 150,000 children in northern Gaza.
All children will need a second dose in four weeks for the vaccine to be effective.
According to the WHO, more than 90 per cent of children in Gaza need to be reached to prevent an outbreak
