Status: affected by circulating vaccine-derived poliovirus
During the week of 3 June 2019, the World Health Organization (WHO) received confirmation of a vaccine-derived poliovirus type 2 (cVDPV2) in Angola, with 10 nucleotide changes from Sabin 2, which is the closest virus match, suggesting it is a new emergence.
The cVDPV2 was isolated from an acute flaccid paralysis (AFP) case, with onset of paralysis on 22 March 2019, from Lunda Norte province, bordering the Democratic Republic of Congo (DR Congo). DR Congo has been affected by known circulating VDPV2 (cVDPV2) outbreaks since early 2017 and has been conducting outbreak response with monovalent OPV type 2 (mOPV2).
Given cross-border population movements, subnational immunity and surveillance gaps, and the fact that poliovirus is a highly infectious pathogen, Lunda Norte province is considered at high-risk for any poliovirus re-introduction or re-emergence. Confirmation of this cVDPV2 underscores this risk, and it is critical that an emergency, preventive outbreak response now be fully implemented in the province. In absence of a timely and high-quality vaccination response, there is imminent risk of further transmission of this cVDPV2, potentially leading to a significant outbreak of paralytic polio.
Two preventive emergency outbreak response campaigns with mOPV2 are planned in Lunda Norte province, to be synchronized with campaigns in neighbouring areas of DR Congo. This synchronization is critical, to ensure virus transmission can be rapidly interrupted, including any potential circulation among mobile populations.
Separately, a second cVDPV2 was also isolated from a further AFP case first detected in Huila province, who subsequently travelled thereafter to Huambo province to seek care. The isolated virus has 6 nucleotide changes from Sabin 2, which is the closest virus match, suggesting that it is also a new emergence. Initial sequencing suggests it is unrelated to the cVDPV2 isolated in Lunda Norte (or any other cVDPV2 isolated elsewhere).
WHO teams are supporting the Ministry of Health and local authorities to undertake full epidemiological and virologic investigations into both emergences, including to ascertain their source and origin of the isolated virus, whether it is linked to mOPV2 use in neighbouring areas, and to determine any potential local spread associated with it. Active surveillance is being strengthened and subnational immunity levels are being analysed. Any decision on further vaccination response will be based on careful assessment in the light of findings of the detailed investigation.
These events further underline the risk of cVDPV2 emergence or spread across Africa.
While investigations into the source of these isolated viruses is important, the overriding priority must be to prevent further children from being paralysed by any potential local circulation of virus or importations from neighbouring countries.
WHO risk assessment
WHO assesses the risk of international spread of cVDPV2 across Africa to be high.
It is important that all countries, in particular those with frequent travel and contacts with polio-affected countries and areas, strengthen surveillance for AFP cases in order to rapidly detect any new virus importation and to facilitate a rapid response. Countries, territories and areas should also maintain uniformly high routine immunization coverage at the district level to minimize the consequences of any new virus introduction.
International Health Regulations
Countries affected by poliovirus transmission are subject to International Health Regulations Temporary Recommendations that request them to declare a case of polio as a national public health emergency and consideration vaccination of all international travellers, as per temporary recommendations issued as of May 2019.
WHO’s International Travel and Health recommends that all travellers to polio-affected areas be fully vaccinated against polio. Residents (and visitors for more than 4 weeks) from infected areas should receive an additional dose of OPV or inactivated polio vaccine (IPV) within 4 weeks to 12 months of travel.