Health officials in Burundi on Friday declared an outbreak of circulating poliovirus after confirming eight cases, the first such detection in over three decades, the World Health Organization said in a statement.
The WHO said the cases were confirmed in an unvaccinated four-year-old boy in Isale district in western Burundi and two other children who were his contacts.
"Additionally, five samples from environmental surveillance of wastewater confirmed the presence of the circulating poliovirus type 2," it added.
Circulating poliovirus type 2 infections can occur when the weakened strain of the virus contained in the oral polio vaccine circulates among under-immunized populations for long periods.