cVDPV Type 1 Outbreak in Lao People’s Democratic Republic in 2015/2016

  • Vaccine preventable diseases
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Background:
Acute Flaccid Paralysis (AFP) is notifiable globally. Oral polio vaccine (OPV) contains an attenuated virus. On very rare occasions, when replicating in the gut, the OPV strains genetically change and may spread in communities that are not fully vaccinated against polio. On 6 October 2015, the National Institute for Infectious Diseases (NIID) in Japan notified the Laos Government and WHO of a case of circulating vaccine-derived polio virus type 1 (cVDPV1) in Bolikhamxay province.

Methods:
We used the standard WHO AFP case definition and applied it to all ages. Stool specimens were collected from cases and close contacts. A confirmed case required VDPV1 to be identified in stool by NIID or to be epidemiologically linked to another case using WHO criteria. In 2016, we enhanced AFP surveillance with a target of three non-polio AFP cases per 100,000 children under 15 years. Rapid response teams conducted active case finding in affected areas.

Results:
A total of 302 AFP cases were reported from all 18 provinces from January 2015 to December 2016. The national AFP detection rate was 6.3 cases per 100,000 in 2016. The majority of the AFP cases (67%) were under 15 years of age. From October 2015 to January 2016, there were 11 AFP cases confirmed as cVDPV1; eight were laboratory confirmed and three were epidemiologically linked. Two cVDPV1 cases died (CFR=18.2%). An additional 25 contacts were cVDPV1 positive. All of the cVDPV1 cases and contacts are of Hmong ethnicity. We conducted ten polio vaccine supplementary immunization activities (SIAs) to interrupt the transmission of cVDPV1.

Conclusion:
The cVDPV1 outbreak signified low levels of immunity against polio in the affected community. All children under 1 year should be vaccinated against polio. Strengthening routine immunization is necessary to ensure Lao PDR and the Western Pacific Region remains polio free.

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