Between 6 and 16 February 2016, the National IHR Focal Point (NFP) of Lao People’s Democratic Republic (PDR) notified WHO of 3 additional cases of vaccine-derived poliovirus type 1 (VDPV1).

Details of the new cases

  • The first case is a 15-month-old female from Phonhoung district, Vientiane Province. The patient developed paralysis on 8 January.
  • The second case is a 44-year-old female from Feuang district, Vientiane Province. The patient developed paralysis on 11 January.

Neither of the two cases received oral polio vaccine (OPV). On 3 February 2016, the National Institute of Infectious Diseases, Japan reported that stool samples for both cases tested positive for type 1 circulating vaccine-derived polio virus (cVDPV1). There is no epidemiological link between the two cases.

  • The third case is an 18-year-old male from Meun district, Vientiane Province. The case developed paralysis on 3 January 2016. Test results for his stool specimen are pending; however, the specimen was considered to be as ‘inadequate’ since it was collected more than 14 days after the onset of paralysis. A stool sample collected from a close contact tested positive for VDPV1, the case is classified as cVDPV1 based on the epidemiological link and the contact’s positive stool sample.

Of note is that these new cVDPV1 isolates are genetically linked but have considerable genetic differences with the previous Laos cVDPV1 isolates from the current outbreak. The new findings suggest that more than one strain of cVDPV1 may have emerged separately and co-circulated in Laos without being detected.

To date, the total number of confirmed cVDPV1 cases in this outbreak is 10. Furthermore, since the beginning of the outbreak, circulating cVDPV1 has been isolated from the stools of 23 healthy contacts in the provinces of Bolikhamxay, Xaisomboun and Vientiane.