Health authorities in the Lao People’s Democratic Republic (PDR) have reported on a case of circulating vaccine-derived poliovirus type 1 (cVDPV1) in a child from the district of Bolikhan, in Bolikhamxay Province.
Lao’s last case of indigenous wild poliovirus was reported in 1993.
The eight-year-old child was confirmed with circulating vaccine-derived poliovirus type 1 (cVDPV1) with an onset of paralysis on Sep. 7. He died four days later.
Genetic sequencing of the virus confirmed on 6 October that it is vaccine-derived and suggests that it has been circulating in the area for more than two years.
The Bolikhan district is known for chronically low immunization rates: reported coverage with 3 doses of oral polio vaccine (OPV) was of 40% to 66% between 2009 and 2014; and 44% in 2015 to date.
A joint team of the Ministry of Health, the World Health Organization, UNICEF and the Lao Office of US Centers for Disease Control and Prevention team traveled to the province for further assessment on 7 October. A rapid survey conducted in the affected village showed low vaccine coverage for OPV. Active case finding in the surroundings of the case’s household is ongoing; stool specimens are being collected from healthy children in the case household and community.
Preparations are under way for large-scale supplementary OPV immunization campaigns covering Bolikhamxay province and several adjacent provinces.
The World Health Organization says circulating vaccine-derived polioviruses (cVDPVs) are rare but well-documented strains of poliovirus mutated from strains in oral polio vaccine (OPV). They can emerge in some populations that are inadequately immunized.
Ending polio for good requires eliminating both wild and vaccine-derived polio, and due to the risk of cVDPVs, use of OPV must be stopped to secure a lasting polio-free world. OPV will be withdrawn in a phased manner, beginning with the removal of type 2-containing OPV. The switch from trivalent to bivalent OPV, planned in April 2016, will reduce the risk of cVDPV substantially (as 90% of cVDPV is caused by type 2) and sets the stage to eventually stop using OPV altogether and transition to the inactivated polio vaccine (IPV), which cannot cause cVDPV.