Recently, there has been new cases of Circulating Vaccine-Derived
Polio Virus 2 (cVDPV2) reported in the Manono and the Ankoro districts of in
the Democratic Republic of Congo where the onset dates where November 9th
and November 17th (one reported case in each) according to the
Global Polio Eradication Initiative (GPEI). There had been no cVDPV2 cases for
months now, and for the year, the total number of cases of cVDPV2 in the Democratic
Republic of Congo has now reached 12 cases, which will probably be the number
for the year considering how close this year is to ending (about time). So how
exactly do cVDVs occur in the first place? Well, in the DNC, oral polio virus
vaccine made from a weak live-attenuated vaccine is used where the virus
replicates in the intestines. In the intestines, the poliovirus is excreted for
6-8 weeks, and during that time, some of the excreted virus may not be the same
as the vaccine poliovirus. What ends up happening is that this new
vaccine-derived poliovirus, if given the right environment where a population has
immunization rates that are low, the vaccine-derived poliovirus can circulate,
mutate, and potentially retain its original neurovirulence. These polioviruses
that have reobtained their pathogenicity are the cVDPVs.
Additionally, the GPEI has made a report this week regarding
wild poliovirus 1 in Pakistan. As a side note, the three remaining countries
where wild-type poliovirus is still endemic around the globe are Pakistan,
Afghanistan, and Nigeria. This case took place in the Kila Abdullah district,
where the total number of WPV1 cases in Pakistan have now reached 8 cases for
2017, where the total number of cases for the year is now 20.
Sources:
-Daniel Gutierrez