Authorities launched a massive polio vaccination campaign on Sunday in Iraq, Syria and Egypt after health officials found a suspected case of the virus in a young boy near Baghdad.
The five-day campaign aims to vaccinate more than 20 million children, including 5.6 million in Iraq alone, UNICEF said, with confirmed cases in conflict-hit neighbouring Syria having sparked a region-wide alert.
"Polio eradication is a global priority," UNICEF's representative in Iraq Marzio Babille said in a statement.
"I appeal to the people of Iraq to join hands in ensuring every child under the age of five is vaccinated during the upcoming April polio campaign, regardless of how many doses they've received previously."
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Last month, Iraq's health ministry said it found a case of polio in a young boy in Bab al-Sham, near Baghdad, the country's first such case in 14 years.
Health ministry spokesman Ziad Tariq said at the time that officials believed the case originated in Syria, which shares a long border with Iraq's restive western province of Anbar.
In early January, anti-government fighters took control of all of the Anbar city of Fallujah, and parts of the provincial capital Ramadi, some of which they still hold.
A total of 27 children have been paralysed by polio in Syria through the end of March, according to the UN, including 18 in Deir Ezzor, the Syrian province across the border from Anbar.
Lebanon and Turkey will join the regional polio vaccination campaign on April 10 and April 18 respectively, according to UNICEF.