The recent vaccine-derived polio outbreaks confirmed in Yemen and Sudan are consequences of increasingly low levels of immunity among children. Each outbreak has paralysed children in areas that have been extremely difficult if not impossible to reach with routine or supplementary polio vaccination for extended periods of time.
These outbreaks do not come as a total surprise. In Sudan, extensive population movement by nomadic communities, people displaced by conflict, frequent movement between neighbouring countries and restricted access in some areas have made it enormously difficult to reach every child with vaccines. The cases in Yemen are clustered in the Sa’adah Governorate in the war-ravaged country’s north-west, an area that has very low routine immunization levels and has been inaccessible to the polio programme for more than two years. The last house-to-house campaigns in this area were in November 2018.
Polio is a devastatingly contagious disease, transmitted from person to person through close contact. The only way to stop it is through vaccination using oral polio vaccine. Vaccine-derived poliovirus outbreaks are a siren call that immunity levels in affected communities have become unacceptably low.