Circulating vaccine-derived poliovirus type 2 – Democratic Republic of the Congo
In the Democratic Republic of the Congo, three different circulating vaccine-derived poliovirus type 2 (cVDPV2) outbreaks have been detected in acute flaccid paralysis (AFP) cases. In February 2018, the government declared cVDPV2 to be a national public health emergency.
The cVDPV2 strain initially detected and reported in June 2017 from Haut Lomami Province spread in late 2017 and early 2018 to Tanganyika and Haut Katanga provinces, respectively. The same virus was confirmed in Ituri Province in June 2018, close to the border with Uganda, from an AFP case with onset of paralysis on 5 May 2018. Investigations are ongoing. WHO assessed the overall public health risk at the national level to be very high and the risk of international spread to be high due to the proximity of the recent detection of the AFP case in Ituri which is close to an international border and with known population movement.
Maniema Province is affected by a separate cVDPV2 outbreak, with two cases confirmed in 2017. The date of onset of paralysis of the most recent case was 18 April 2017. So far, no new cases have been detected in 2018, and there is no evidence that this virus has spread further geographically.
The third and most recently detected outbreak of cVDPV2 was found in Mongala Province and isolated from an AFP case in the Yamongili Health Zone. The onset date of paralysis was 26 April 2018. Circulation of the strain was confirmed when the same strain was isolated in stool specimens from two healthy community contacts.
Figure 1. Distribution of cVDPV2 cases from 1 January through 29 June 2018 in the Democratic Republic of the Congo
Public health response
WHO and partners are responding to these outbreaks, including through the use of monovalent oral polio vaccine type 2 (mOPV2) in line with internationally-agreed upon outbreak response protocols. However, operational gaps in the response continue to hamper the full implementation of these protocols, as high-risk populations remain under-immunized, and the response thus far has not controlled the outbreak nor prevented its spread.
The geographic extent of the outbreak response to all three strains is now being re-evaluated, given the confirmed spread of one of the strains to Ituri and confirmation of the new strain in Mongala.
Surveillance and immunization activities are being strengthened in neighbouring countries.
In February 2018, the government declared cVDPV2 to be a national public health emergency. The remaining operational gaps in the outbreak response must be urgently addressed.
WHO risk assessment
WHO assessed the overall public health risk at the national level to be very high and the risk of international spread to be high. This risk is magnified by known population movements between the affected area of Democratic Republic of the Congo, Uganda, Central African Republic and South Sudan, and the upcoming rainy season which is associated with increased intensity of virus transmission.
The detection of cVDPV2s underscores the importance of maintaining high routine vaccination coverage everywhere to minimize the risk and consequences of any poliovirus circulation. These events also underscore the risk posed by any low-level transmission of the virus. A robust outbreak response is needed to rapidly stop circulation and ensure sufficient vaccination coverage in the affected areas to prevent similar outbreaks in the future. WHO will continue to evaluate the epidemiological situation and outbreak response measures being implemented.
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 travelers 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 inactivated polio vaccine (IPV) within four weeks to 12 months of travel. As per the advice of the Emergency Committee convened under the International Health Regulations (2005), efforts to limit the international spread of poliovirus must continue as it 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 travelers.
WHO does not recommend any restrictions on travel and/or trade to the Democratic Republic of the Congo on the basis of the information available for the current cVDPV2 outbreaks.