By David Loyn BBC correspondent

Polio, which can maim or kill children, has been virtually wiped out in the developed world but Iraq's shattered health system makes it uniquely vulnerable.

The last major outbreak there occurred as recently as 1999.

Iraq's health system has suffered under sanctions

Despite the imminent threat of war, Unicef is going ahead with a vaccination programme at the end of next week.

In order to work it is important that all children are vaccinated at the same time which will involve 14,000 health workers going out across the country, aiming to protect millions of children.

Unicef is also trying to vaccinate more children against measles.

The Secretary General Carol Bellamy said she hopes that peace will prevail but Unicef is ready if war comes.

Preparations

Hundreds of tonnes of food aid are already pre-positioned in countries surrounding Iraq to deal with the expected flood of refugees if bombs start to fall.

The concern of many international agencies is that people who are already dependent on food aid will face added hardship if there is a war which goes on for any time at all.

A quarter of Iraq's people have no access to clean drinking water and a third of its children are malnourished.

If America goes to war without UN Security Council backing the job of UN agencies in mopping up after a war would be made that much harder.