Nigeria, Yemen, DR Congo account for more than 85% of vaccine-derived polio cases in 2022

•Blames outbreaks on inaccessibility, insecurity, high concentration of zero dose children, population displacement
•WHO says cases in Algeria linked to viruses circulating in Nigeria
•Says cases in Benin, Ghana, Togo, Côte d’Ivoire resulted from reinfection by new international spread from Nigeria

A World Health Organisation (WHO) committee on polio, yesterday, said Northern Yemen, eastern Democratic Republic of Congo and northern Nigeria continue to account for more than 85 per cent of the global circulating Vaccine Derived Polio Viruses (cVDPV2) caseload.

A vaccine-derived poliovirus (VDPV) is a strain related to the weakened live poliovirus contained in oral polio vaccine (OPV). If allowed to circulate in under or unimmunised populations for long enough, or replicate in an immuno-deficient individual, the weakened virus can revert to a form that causes illness and paralysis.

The thirty-third meeting of the Emergency Committee under the International Health Regulations (2005) (IHR) on the international spread of poliovirus convened by the WHO Director-General, in a statement, said there have been four new countries reporting cVDPV2 – Algeria, Israel, the United Kingdom of Great Britain and Northern Ireland and the United States of America. It said the viruses detected in the latter three countries are genetically linked indicating long-distance international spread through air travel has occurred.

The Emergency Committee reviewed the data on wild poliovirus (WPV1) and cVDPV in the context of global eradication of WPV and cessation of outbreaks of cVDPV2 by end of 2023.

The committee said the virus in Algeria is genetically linked to viruses circulating in Nigeria and is therefore an importation due to international spread. “Furthermore, the detection of cVDPV2 in Benin, as has been seen in Ghana, Togo and Côte d’Ivoire appears to have resulted from reinfection caused by new international spread from Nigeria,” it noted.

The WHO committee said three new countries have reported cVDPV1 – Democratic Republic of the Congo, Malawi and Mozambique.

The committee noted that much of the risk for cVDPV outbreaks could be linked to a combination of inaccessibility, insecurity, a high concentration of zero dose children and population displacement. These, it said, have been most clearly evidenced in northern Yemen, northern Nigeria, south central Somalia and eastern DRC. Despite the ongoing decline in the number of cases and lineages circulating, the recent episodes of international spread of cVDPV2 indicate the risk remains high.

Although encouraged by the reported progress, the Committee unanimously agreed that the risk of international spread of poliovirus remains a Public Health Emergency of International Concern (PHEIC) and recommended the extension of Temporary Recommendations for a further three months. The Committee recognised the concerns regarding the lengthy duration of the polio PHEIC and the importance of exploring alternative IHR measures in the future but concluded that there are still significant risks as exemplified by the importation and continued transmission of virus in Malawi and Mozambique.

The Committee recognises that border vaccination may not be feasible at very porous borders in Africa but was concerned by the lack of synchronisation and cross border coordination in response to the WPV1 importation in southeast Africa. Outbreak response assessments are being carried out currently and urged the countries most directly involved in the response – Malawi and Mozambique – to facilitate these assessments. The committee also noted with concern that most AFP cases were being detected during campaigns and more systematic surveillance efforts are required including training of clinicians to identify and respond to AFP cases. Noting the acute humanitarian crisis still unfolding in Afghanistan, the committee urged that polio campaigns be integrated with other public health measures wherever possible including malnutrition screening, vitamin A administration and measles vaccination. The committee also strongly encouraged house to house campaigns be implemented wherever feasible as these campaigns enhance identification and coverage of zero dose and under-immunised children.

In Pakistan, the opportunity to interrupt polio transmission in the coming low season, noting that the reported cases are geographically limited to south KP with positive environment isolates detected elsewhere in KP, Punjab and Sindh. The committee urged Pakistan to grasp the upcoming opportunity.

The committee noted the situation in northern Yemen with concern where it is estimated several million children have still not been accessed for immunization. The committee strongly encouraged more urgent dialogue with all relevant stakeholders to enable children to be vaccinated and protected.

The cVDPV2 outbreaks in Jerusalem, London and New York highlight the importance of sensitive polio surveillance, including environmental surveillance, in all areas where there are high risk sub-populations, and the committee urges all countries to take heed of the lesson learnt through this event and take steps to improve polio surveillance everywhere that such risks exist.