Wild poliovirus outbreak in Malawi and prospects for the Eastern Mediterranean Region
The Ministry of Health of Malawi reported on 17 February 2022 an outbreak of wild poliovirus type 1 (WPV1) after a case was detected in a young child in the capital Lilongwe. WHO is supporting the Malawi health authorities to carry out a risk assessment and outbreak response, including through a supplementary immunization campaign.
This new WPV1 case confirmed in Malawi (map) is significant as it is the first case of wild poliovirus to be detected in Africa in more than five years. The case is a 45 month -old female with onset on 19 November 2021. She is a resident in Central Lilongwe and presented with paralysis of the right arm and leg, and fever of sudden onset.
Sequencing has grouped the Malawi cluster as YC2 – with the closest match being a Pakistan WPV1 sequence detected in 2019 in Sindh Province (table).
The last case of WPV in the WHO African Region was reported in 2016 in northern Nigeria. The African Region was declared free of indigenous WPV in August 2020 after Nigeria had passed three years without any trace of WPV. This new case in Malawi has been categorized as imported from the WHO Eastern Mediterranean Region and thus does not affect the African Region’s certification status as free of WPV.
Polio is a highly infectious disease that mainly affects children under five years of age. The virus is transmitted person-toperson and spreads mainly through the faecal-oral route or, less frequently, by a common vehicle (for example, contaminated water or food) before multiplying in the intestine. Initial symptoms are fever, fatigue, headache, vomiting, stiffness of the neck and pain in the limbs. Poliovirus invades the nervous system, and can cause total paralysis in a matter of hours. One in 200 infections leads to irreversible paralysis (usually in the legs). Among those paralysed, 5% to 10% die when their breathing muscles become immobilized.
There are three strains of WPV (type 1, type 2 and type 3). WPV2 was eradicated in 1999, and no case of WPV3 has been found since the last reported case in Nigeria in November 2012. Silent circulation of polio can complicate control measures as only one in 200 infected children will present with paralysis.
The fourth meeting of the Regional Subcommittee on Polio Eradication and Outbreaks convened on 9 February 2022.
The Subcommittee declared the ongoing circulation of any strain of poliovirus in the Eastern Mediterranean Region to be a regional public health emergency and called on all governments to enable uninterrupted access to the youngest and most vulnerable children through the resumption of house-to -house vaccination campaigns.
The spread of polio in the Eastern Mediterranean Region is a pressing emergency and it remains a Public Health Emergency of International Concern (PHEIC) under the International Health Regulations (2005). Subcommittee members noted a sharp decrease in cases of WPV in Afghanistan and Pakistan in 2021 but warned against complacency as outbreaks of circulating vaccine-derived polioviruses type 1 (cVDPV1) and type 2 (cVDPV2) continued to emerge and spread in the Eastern Mediterranean Region in 2021. As of February 2022, Afghanistan, Djibouti, Egypt, Pakistan, Somalia, Sudan and Yemen are responding to transmission of vaccine-derived polioviruses.
While it is not yet clear when and how this imported virus arrived in Malawi and how far it may have spread, this new case is a setback for the global campaign to end polio once and for all. However, the Global Polio Eradication Initiative, supported by WHO and partners, will work to limit the damage by implementing a vaccination strategy that can quickly contain the outbreak.
Source: World Health Organization