Around 288,000 children aged 0 to 15 years are being targeted in the campaign, according to a news release issued by the World Health Organization (WHO) and the UN High Commissioner for Refugees (UNHCR).

Since the first case was discovered on 17 May, laboratory tests have confirmed that four more people have polio, a highly infectious disease caused by a virus that invades the nervous system and can cause total paralysis in a matter of hours.

The first round of vaccinations will be completed today, the agencies said. The next round, which begins in one week, will target the whole refugee population in Dadaab – some 424,000 people. The campaign will have four rounds in total.

At the same time, the Kenyan Ministry of Health is also conducting a vaccination campaign among the host community population in North Eastern Province in close collaboration with WHO.

The polio outbreak in Dadaab comes after a similar outbreak in Somalia, where one case has been reported in the capital, Mogadishu. The Somali Government has expressed concern about the situation in south-central Somalia, where immunization activities have not taken place for the last three years because of the security situation.

Currently, only three countries – Nigeria, Afghanistan and Pakistan – are polio endemic.