"In recent weeks, the UN worked to vaccinate 4.7 million Iraqi children five years and under ... as part of a series of initiatives aimed at bolstering health among the population," the statement in the Jordanian capital, Amman, said on Sunday.
In an effort to reach the largest number of people, the UN, with the support of private mobile phone service providers, sent text messages to announce the polio immunisation campaign.
"This support by private companies demonstrated the spirit of corporate civil responsibility emerging in Iraq," the statement said on the eve of a two-day international donors' conference hosted by Jordan.
According to the UN, an "alarming rise in the incidence of polio cases in nearby Yemen" prompted the immunisation campaign across Iraq.
"With considerable numbers of people moving across that country's border (Yemen) with Saudi Arabia, health officials warn of a growing potential for the disease to be 'imported' to Iraq," the statement said.
The UN donated more than 10 million doses of oral polio vaccine to Iraq over the past year as part of a nationwide drive to rehabilitate the health sector in the violence-ridden country.
The UN and the World Bank administer a $1 billion trust fund for Iraq set up by international donors to rebuild the country.