Polio is again circulating in the Horn of Africa, the World Health Organization said.

Two children have recently been found to have the type of paralysis caused by polio — one in the southern part of Somalia and the other in a Kenyan camp that includes many Somali refugees.

Two healthy children related to the second child also had evidence of infection. Only about one infection in 200 causes paralysis, but the rest can silently shed the virus, which is spread by fecal-oral contact, often through sewage gutters and dirty puddles.

The Global Polio Eradication Initiative recently vaccinated 450,000 children in southern Somalia. It plans to vaccinate 2.1 million children there and in neighboring eastern Kenya by June, and then to repeat that in July and again in August.

If the outbreak is not quickly contained, the consequences could be far-reaching. From 2002 to 2005, the virus spread from Nigeria, where it has never been wiped out, to 21 other countries, paralyzing more than 1,000 victims.