WHO puts East Africa on high alert over Polio virus cases detection  

EAST AFRICA— The World Health Organisation (WHO) has put the East African region on high alert after Global Polio Eradication Initiative (GPEI), has confirmed Circulating vaccine-derived poliovirus-type (cVDPV2) cases in Kenya and Tanzania.

WHO situational analysis of the Kenyan case

On 11 July 2023, WHO received an official report regarding the detection of cVDPV2 in two acute flaccid paralysis (AFP) cases and two asymptomatic healthy children.

Both cases were from Hagadera refugee camp, in Kenya, the second largest refugee camp in the world with over 100,000 refugees.

The genetic sequencing analyses showed that all four isolates are genetically linked to the cVDPV2 circulating in Banadir, Somalia.

According to the WHO-UNICEF estimates of national immunization coverage, oral polio vaccine third dose (OPV3) and inactivated poliovirus vaccine first dose (IPV) was 91% in Kenya in 2021.

However, the coverage in the Hagadera camp is 77% for both OPV3 and IPV as of May 2023.

WHO assesses the overall risk at the national level to be high due to the overcrowded living conditions in the refugee camp, high rate of malnutrition, and poor water and sanitation facilities.

WHO further notes that mass and frequent population movements with Somalia, the influx of new arrivals to the camp, late identification of the newly arrived children, high prevalence of zero dose children among the newly arriving children from middle and lower Juba Somalia, and sub-optimal surveillance performance.

Activation of Public health response measures

Kenya’s Ministry of Health (MoH), with support from the GPEI, has conducted a risk assessment, along with a field investigation.

The MoH, through the Division of Disease Surveillance and Response and the Public Health Emergency Operations Centre, has activated a Technical Coordination Committee to begin preparations for the implementation of the emergency outbreak response.

Moreover, Sub National Immunization Days (SNIDs) with nOPV2 have been planned as part of the rapid response.

Critically, the first round of the vaccination campaign in August will vaccinate all children under 5 years of age targeting Garissa County, the epicenter of the outbreak, and neighboring counties with a Somali community as well as Nairobi (the capital), due to population movements.

A second and third round with the expansion of targeted areas is being planned to be conducted in September and October.

The Situation in Tanzania

On 4 July 2023, the Ministry of Health of the United Republic of Tanzania notified WHO of the detection of cVDPV2 in the country.

The virus was isolated from a case of acute flaccid paralysis (AFP) in the Rukwa region, southwestern Tanzania bordering Lake Tanganyika to the west and Zambia to the south.

Furthermore, gene sequencing of the isolated virus has indicated close linkage with the cVDPV2 circulating in South Kivu, DRC.

The public health authorities of the Ministry of Health are conducting further field investigations including strengthening the AFP surveillance for the detection of additional AFP cases and subnational level immunity gap analysis to identify potential un-or under-immunized populations and/or areas to guide public health response activities.

WHO assesses the overall risk at the national level to be high due to the sub-optimal surveillance performance in some districts, sub-optimal vaccination coverage resulting in low population immunity, and the ongoing population movement across neighboring countries.

Since 2022, Tanzania has been actively participating in a multi-country outbreak response across southeast Africa, in response to the detection of different strains of poliovirus in the sub-region.

According to the WHO-UNICEF estimates of national immunization coverage, the oral polio vaccine third dose (OPV3) and the inactivated polio vaccine first dose (IPV1) was 88% in 2022 in Tanzania.

Public health response

A risk assessment is being conducted, led by the Ministry of Health, and supported by GPEI, along with a field investigation and planning of appropriate response.

The capacity of the country’s AFP surveillance has been strengthened to detect additional AFP cases.

Subnational immunity levels are being analyzed to identify potential un-or under-immunized populations and/or areas.

While new WHO and UNICEF data show promising signs of immunization services rebounding in some countries, coverage still falls short of pre-pandemic levels putting children at risk from disease outbreaks, particularly in low-income countries. 

In response to these latest published data, the members of the Immunization Agenda 2030 Partnership Council called for further strengthened efforts (Immunization Agenda 2030) for immunization recovery.

The Run down on cVDPV2

Polio is a highly infectious disease that largely affects children under five years of age, causing permanent paralysis (approximately 1 in 200 infections) or death (2-10% of those paralyzed).

The virus is transmitted from person-to-person, mainly through the fecal-oral route or, less frequently, by a common vehicle (e.g., contaminated water or food) and multiplies in the intestine, from where it can invade the nervous system and cause paralysis.

The incubation period is usually 7-10 days but can range from 4-35 days.

Up to 90% of those infected are either asymptomatic or experience mild symptoms and the disease usually goes unrecognized.

Vaccine-derived poliovirus is a well-documented strain of poliovirus mutated from the strain originally contained in OPV.

OPV contains a live, weakened form of poliovirus that replicates in the intestine for a limited period, thereby developing immunity by building up antibodies.

Rarely, when replicating in the gastrointestinal tract, OPV strains genetically change and may spread in communities that are not fully vaccinated against polio, especially in areas where there is poor hygiene, poor sanitation, or overcrowding.

The lower the population’s immunity, the longer this virus survives and the more genetic changes it undergoes.

Hardly, the vaccine-derived virus can genetically change into a form that can cause paralysis as does the wild poliovirus – this is what is known as a vaccine-derived poliovirus (VDPV).

The detection of VDPV in at least two different sources and at least two months apart, that are genetically linked, showing evidence of transmission in the community, is classified as ‘circulating’ vaccine-derived poliovirus type 2 (cVDPV2).

WHO overall assessment and recommendations of the East African polio cases

WHO has considered the risk of international spread and/or emergence of cVDPV2 of this strain to be high.

Particularly, across other areas of the Horn of Africa, due to the low population immunity, the use of trivalent OPV (tOPV) in Somalia, suboptimal surveillance, inadequate routine immunization levels in some areas, and large-scale population movements.

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 4 weeks) from infected areas should receive an additional dose of OPV or IPV within 4 weeks to 12 months of travel.

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