UN staff plan to immunise every five-year-old they find

The first round of the current campaign took place in October, with mostly West African countries targeted.

Just over 10 years ago it was estimated that polio was infecting 1,000 children worldwide daily.

Immunisation has reduced that figure dramatically.

But the disease continues to thrive in western and central Africa.

Safe passage

Conflicts in the region and widespread migration have prevented thorough immunisation programmes in the past.

But this time the UN believes that it has secured safe passage for its teams.

Targeted countries

Benin Burkina Faso Cameroon Cape Verde Central African Republic Chad Gambia Ghana Guinea Guinea-Bissau Ivory Coast Liberia Mali Mauritania Niger Nigeria Senegal Sierra Leone Togo

UN staff will go from house to house placing two drops of the vaccine in the mouth of every child under five they find.

The polio virus is vulnerable to eradication because it has no natural home outside the human body.

Health experts believe that if 80% of people in infected populations are vaccinated, that will be enough to break its chain of transmission.

The current campaign aims to completely halt wild poliovirus transmission within two years.

Signs in recent years have been encouraging - only 1,149 cases have been registered this year compared with 7,000 last year.

Just 12 years ago there were at least 350,000 cases.