Circulating vaccine-derived poliovirus type 2 – Syrian Arab Republic
A circulating vaccine-derived poliovirus type 2 (cVDPV2) outbreak has been confirmed in the Deir Al Zour Governorate of the Syrian Arab Republic. There is evidence of genetic linkage among three isolates of type-2 vaccine-derived polioviruses (VDPV2) isolated in the stool specimens of two acute flaccid paralysis (AFP) cases with dates of onset of paralysis on 5 March and 6 May 2017, and the contact specimen of an AFP case collected on 17 April 2017. Al Mayadeen was also the epi-centre of the wild poliovirus type 1 (WPV1) outbreak in Syrian Arab Republic in 2013. Aggressive multi-country polio outbreak response effectively controlled the WPV1 outbreak and no WPV1 case has been reported in Syrian Arab Republic since 21 January 2014.
Public health response
Since the confirmation of the first VDPV2 during May 2017, AFP surveillance has been intensified in the Governorate, especially in the Al Mayadeen district. As of 6 June 2017, a total of 58 AFP cases have been reported from the Governorate this year. In addition to the two cases that have tested positive for VDPV2, a further 11 have tested negative for polioviruses, with the remaining samples being under process in the laboratories or being transported to the laboratories.
Subsequent to the confirmation of the cVDPV2 outbreak, outbreak response planning is underway, including planning for supplementary immunization activities (SIAs) with monovalent oral polio vaccine type 2 (mOPV2), in line with internationally-agreed outbreak response protocols.
Although access for vaccination is compromised due to prevailing insecurity in Deir Al Zour, the Governorate has been partially reached by several vaccination campaigns against polio and other vaccine-preventable diseases since the beginning of 2016. Most recently, two campaigns have been conducted in March and April 2017 using bivalent oral polio vaccine (bOPV). The most recent full trivalent oral polio vaccine (tOPV) round was conducted in October 2015; while tOPV rounds conducted in the first four months of 2016 only reached part of the target population of the Deir Al Zour Governorate. It is pertinent to mention that Syrian Arab Republic introduced two doses of inactivated polio vaccine (IPV) in the routine infant immunization schedule in 2008. Syrian Arab Republic switched from tOPV to bOPV for routine immunization on 1 May 2016.
A detailed risk analysis is currently being updated, including assessing overall population immunity levels and strengthening active searches for additional cases of AFP. Surveillance and immunization activities are being strengthened in neighbouring countries as well.
WHO risk assessment
The detection of cVDPV2 underscores the importance of maintaining high levels of routine vaccination coverage at all levels to minimize the risk and consequences of any poliovirus circulation. Such events also underscore the risk in areas or regions with continued substantial insecurity that hampers maintaining high population immunity through routine vaccination. A robust outbreak response is needed to rapidly stop the VDPV2 transmission. WHO will continue to evaluate the epidemiological situation and outbreak response measures being implemented.
It is important to complete the ongoing risk assessment as soon as possible to inform the vaccination response with mOPV2 and IPV. The geographical scale of the vaccination response will be in accordance with the findings of the risk assessment. It will be critical to achieve the highest possible coverage during the vaccination response. Given the difficult and challenging security situation in the area, appropriate strategies will be identified and utilized to implement the response. Intensified AFP surveillance should continue.
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.
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 four weeks) from infected areas should receive an additional dose of OPV or IPV within four weeks to 12 months prior to the travel.
As per the advice of an Emergency Committee convened under the International Health Regulations (2005), efforts to limit the international spread of poliovirus remains a Public Health Emergency of International Concern (PHEIC). Countries affected by poliovirus transmission are subject to Temporary Recommendations. To comply with the Temporary Recommendations issued under the PHEIC, any country infected by poliovirus should declare the outbreak as a national public health emergency and consider vaccination of all international travellers.