What are Vaccine-derived polioviruses (VDPVs)?
The Global Polio Eradication Initiative defines it as follows: The oral polio vaccine contains a live, attenuated (weakened) vaccine-virus. When a child is vaccinated, the weakened vaccine-virus replicates in the intestine and enters into the bloodstream, triggering a protective immune response in the child. Like wild poliovirus, the child excretes the vaccine-virus for a period of six to eight weeks. Importantly, as it is excreted, some of the vaccine-virus may no longer be the same as the original vaccine-virus as it has genetically altered during replication. This is called a vaccine-derived poliovirus.
During the past week, Madagascar reported an additional case of circulating vaccine-derived poliovirus type 1 (cVDPV1) in with onset of paralysis in Mahalapye district of Mahalapye province. In Madagascar, the total number of cVDPV1 cases for 2015 is now 9.
One such case was reported in Madagascar in 2014.
No cases of wild poliovirus 1 (WPV-1) were reported during the past week in any of the three polio endemic countries (Pakistan, Afghanistan and Nigeria).