Circulating vaccine-derived poliovirus type 2 – African Region
Outbreaks of circulating vaccine-derived poliovirus type 2 (cVDPV2) have been reported in several countries in West Africa, central Africa and Horn of Africa (for more information, please see the disease outbreak news published on 31 July 2019). This report provides a situational update on current cVDPV2 outbreaks in newly affected countries in Africa. No wild poliovirus has been detected on the continent since September 2016.
A. West Africa and Lake Chad Basin (LCB) sub-region
In West Africa and the Lake Chad sub-region, a cVDPV2 outbreak originating from Jigawa state, Nigeria, continues to spread. Following detection of this outbreak in Cameroon, Ghana, Benin and the Republic of Niger earlier this year and in 2018, the virus has now been detected in Chad, Togo and Côte d’Ivoire.
On 16 October 2019, cVDPV2 was isolated from a child under five years old with acute flaccid paralysis (AFP) in Mandelia sub-prefecture in Chari Baguirmi province, western Chad bordering Cameroon. Onset of paralysis was on 9 September. Samples were collected on 16 and 17 September 2019. The isolated virus was reported to be genetically different from Sabin 2 with 32 nucleotide changes. The affected geographical area has previously not participated in a monovalent oral polio vaccine type 2 (mOPV2) vaccination campaign.
As of 28 October 2019, there is one case of cVDPV2 reported in the country. According to the WHO-UNICEF routine immunization estimates, inactivated poliovirus vaccine (IPV) coverage in children under the age of one was estimated to be 41% in 2018.
On 15 October 2019, cVDPV2 was isolated from a child under five years old with AFP in Est-Mono district in Plateaux province, bordering Benin to the east and Ghana to the west, with the onset of paralysis on 13 September 2019. Samples were collected on 18 and 19 September 2019. The isolated virus was genetically different from Sabin 2 by 35 nucleotide changes. The affected geographical area has previously not participated in a mOPV2 vaccination campaign.
This is the first-ever reported cVDPV2 outbreak in the country and is genetically linked to the outbreak originating in Jigawa state, Nigeria. As of 28 October 2019, there is one case of cVDPV2 reported in the country. According to the WHO-UNICEF routine immunization estimates, IPV coverage in children under the age of one was estimated to be 20% in 2018 due to the delay in its introduction to the routine immunization schedule in October 2018. The last indigenous wild poliovirus was reported in 1999.
One cVDPV2 positive environmental sample was reported from Adjame-Plateau-Attecoube in Abidjan province. The sample was collected on 26 September 2019. This positive sample is linked to the outbreak in Jigawa state, Nigeria.
B. East and Southern Africa
In Zambia, a cVDPV2 was isolated from a child under five years old with AFP and onset of paralysis on 16 July 2019 from Chiengi in Luapula province, Zambia, bordering Haut Katanga province of the Democratic Republic of the Congo (DRC). As part of the investigation, 34 samples were collected from close contacts and community members on 24 and 29 July 2019 and the isolated virus was genetically different from Sabin 2 by 9 nucleotide changes. Two of the samples from community contacts tested positive for VDPV2 on 17 September 2019. Gene sequencing confirmed the presence of cVDPV2 in the two samples on 17 October 2019, with 9 and 10 nucleotide changes and genetic links to the index case. The affected geographical area has previously not participated in a mOPV2 vaccination campaign.
The current cVDPV2 outbreak is the first outbreak reported in Zambia. As of 28 October 2019, the country has reported one cVDPV2 case. IPV was introduced in Zambia in June 2018 due to global supply shortage, and according to the WHO-UNICEF routine immunization estimates, IPV coverage in children under the age of one was estimated to be 36% in 2018. The last indigenous wild poliovirus case was reported in 1995.
Furthermore, outbreaks of cVDPV2 were reported in other countries in central Africa and the horn of Africa. These countries include Democratic Republic of the Congo, Central African Republic, Angola, Ethiopia, Somalia, Kenya. Additionally, cVDPV2 outbreak has also been reported in Mozambique.
Public Health Response
Partners of the Global Polio Eradication Initiative (GPEI) are providing support as required to affected Ministries of Health. Epidemiological and virological field investigations are ongoing to ascertain the source and origin of the isolated viruses; active surveillance is being strengthened; subnational population immunity levels are being assessed; and, preparedness for outbreak response is being conducted. A more detailed public health response by country is summarized below.
A. West Africa and Lake Chad Basin (LCB) sub-region
Following the confirmation of the cVDPV2 on 16 October, the Minister of Health in Chad declared the outbreak a national public health emergency on 19 October. The immediate response campaign was conducted from 2 to 5 November in the district of Mandalea targeting 51,800 children under five years old using mOPV2. The first round of the polio campaign was conducted from 21 to 25 November and the second round is planned for 13 to 17 December covering 12 districts and targeting 789,418 children under five years old.
Following the confirmation of the cVDPV2 on 15 October 2019, the Minister of Health in Togo declared the outbreak a national public health emergency on 25 October. A risk assessment was conducted and presented to the Advisory Group on 23 October 2019. The immediate response campaign using mOPV2 was conducted from 7 to 10 November 2019 in four districts (Est Mono, Thamba, Anie and Blitta) targeting 132,404 children under five years old. The first round of the polio campaign was conducted from 21 to 24 November 2019 and the second round is planned for 05 to 08 December 2019 covering two regions (Plateaux and Centrale regions) and 17 districts targeting 513,768 children under five years old.
WHO is working with the Ministry of Health to strengthen surveillance.
B. East and Southern Africa
Following the confirmation of the cVDPV2 on 17 October 2019, the Minister of Health in Zambia declared the outbreak a national public health emergency on 18 October 2019. The immediate response campaign using mOPV2 was conducted from 6 to 12 November 2019 in the four districts of Chienge, Nchelenge, Kaputa and Nsama targeting 141,312 children under five years old. The first round of the polio campaign is planned for 26 November to 2 December 2019 and the second round is planned for 17 to 23 December 2019 covering eleven districts and targeting 337,215 children under five years old (for each round).
WHO risk assessment
Given cross-border population movements, suboptimal immunity and surveillance gaps, and waning mucosal immunity to type 2 poliovirus, the risk of further spread or emergence of cVDPV2 in Africa remains high. The detection of cVDPV2s underscores the importance of maintaining high routine vaccination coverage everywhere to minimize the risk and consequences of any poliovirus circulation. In affected areas and identified high-risk areas, it is critical that emergency and high-quality outbreak response be fully implemented.
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 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.
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.