MAIDUGURI, Nigeria

The UN and its World Health Organization agency (WHO) on Friday called for more surveillance of polio to prevent the virus' return to Africa.

Visiting the last survivors of polio cases in Nigeria and Africa, Edward Kallon, UN resident coordinator in Nigeria, asked nations to step up vaccination to ensure polio is not reintroduced to the continent.

"We should not be complacent, we should continue to ensure children are vaccinated at the appropriate ages and [with the] right vaccine to ensure this thing does not repeat itself," Kallon said.

Walter Mulombo, the WHO's country representative, said two Asian countries still have cases of wild poliovirus.

He urged nations to be vigilant, as polo anywhere in the world could spread to other places.

Nigeria was declared polio free in late August by the Africa Regional Certification Commission, an independent regional body for polio and disease outbreak assessment. Before then, it was the only African nation left with the virus.

Polio, an acute infectious disease that causes paralysis, usually affects children under 5. Afghanistan and Pakistan are the only countries in the world with the virus.

After four years without a single case of wild polio, the African region last month was certified free of wild poliovirus.

The announcement was made at a virtual session of the 70th WHO Regional Committee for Africa.