GENEVA (Reuters) - The United Nations is hoping that battles against Islamic State in Syria will calm sufficiently for it to carry out a vaccination drive against polio, starting on Saturday, U.N. agencies said on Wednesday.

A health worker administers polio vaccination to a child in Raqqa, eastern Syria November 18, 2013. REUTERS/Nour Fourat

The World Health Organization is trying to eradicate polio globally, so the 27 cases of the crippling childhood disease that have surfaced around the Syrian battlefields of Deir al-Zor and Raqqa represent a small but crucial setback.

The United Nations is “in communication with all parties in Deir al-Zor and Raqqa regarding ceasefire days” to allow the vaccination campaign to go ahead, the United Nations’ children’s agency UNICEF said in a polio situation report.

It did not say whether the United Nations was talking directly to Islamic State fighters, who are under assault by U.S.-backed forces in Raqqa city and besieging Syrian government forces in Deir al-Zor, nor did it say if any party had agreed to observe a ceasefire on any part of the battlefield.

Other U.N. agencies confirmed the hope of carrying out vaccinations.

“Generally what tends to happen in such circumstances is that any and all parties are engaged in one form or another,” said World Health Organization spokesman Oliver Rosenbauer.

“This might be through formal negotiations via a government or directly with one of the U.N. partners such as WHO or UNICEF, or through third parties, health providers, NGOs, networks, local communities, etc, who are already on the ground, and who can help secure a safer environment for the operations.”

Polio tends to break out in war zones because poor vaccine coverage leaves gaps in the immunity of the local population, leaving children susceptible. The WHO previously tackled a polio outbreak in the same area of Syria in 2013-2014.

Two rounds of immunization are planned, the first starting on about July 22, the second in August. The exact dates may vary in some areas given the evolving on-the-ground situation, Rosenbauer said.

“In areas with conflict, or access issues or large scale population movements, campaigns are conducted more opportunistically, as and when windows of opportunities arise,” he said.

Since the start of the year there have been 87 cases of paralysis in Deir al-Zor governorate, including 66 in Mayadin district, 10 from Deir al-Zor and 11 from Boukamal, while Raqqa governorate has had 14 - six from Raqqa, seven from Tal Abyad and one from Thawra district, UNICEF said.

Of those, 26 cases in Deir al-Zor have been confirmed as polio, and one in Raqqa governorate.

The first round of vaccinations in Deir al-Zor will target 328,000 children, with 355 teams going house-to-house in affected villages and at fixed points in other areas, while the campaign in Raqqa governorate will target 120,000 children.