It’s been several months since any new cases of type 2 circulating vaccine-derived poliovirus (cVDPV2) have been reported in the Democratic Republic of Congo (DRC); however, the Global Polio Eradication Initiative (GPEI) reported this week about two additional cases.
The two new cases–one in Manono district, and one in Ankoro district, Tanganika province had onset dates of Nov. 9 and Nov. 17, respectively. This brings the total cVDPV2 cases in DRC this year to 12.
According to GPEI, Vaccine-derived polioviruses (VDPVs) are rare strains of poliovirus that have genetically mutated from the strain contained in the oral polio vaccine. 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 VDPV.
On very rare occasions, if a population is seriously under-immunized, there are enough susceptible children for the excreted vaccine-derived polioviruses to begin circulating in the community. If the vaccine-virus is able to circulate for a prolonged period of time uninterrupted, it can mutate and, over the course of 12-18 months, reacquire neurovirulence. These viruses are called circulating vaccine-derived polioviruses (cVDPV).
In addition, this week GPEI reported on an additional new case of wild poliovirus type 1 (WPV1) in Pakistan, in Kila Abdullah district, Balochistan province, with onset of paralysis on 13 November. The total number of WPV1 cases in Pakistan in 2017 is now 8 and 20 total WPV1 cases total for 2017.
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