Update on Wild Poliovirus Type 1 Outbreak - Southeastern Africa, 2021-2022

Abstract

Since the Global Polio Eradication Initiative (GPEI) began in 1988, the number of wild poliovirus (WPV) cases has declined by >99.99%. Five of the six World Health Organization (WHO) regions have been certified free of indigenous WPV, and WPV serotypes 2 and 3 have been declared eradicated globally (1). WPV type 1 (WPV1) remains endemic only in Afghanistan and Pakistan (2,3). Before the outbreak described in this report, WPV1 had not been detected in southeastern Africa since the 1990s, and on August 25, 2020, the WHO African Region was certified free of indigenous WPV (4). On February 16, 2022, WPV1 infection was confirmed in one child living in Malawi, with onset of paralysis on November 19, 2021. Genomic sequence analysis of the isolated poliovirus indicated that it originated in Pakistan (5). Cases were subsequently identified in Mozambique. This report summarizes progress in the outbreak response since the initial report (5). During November 2021-December 2022, nine children and adolescents with paralytic polio caused by WPV1 were identified in southeastern Africa: one in Malawi and eight in Mozambique. Malawi, Mozambique, and three neighboring countries at high risk for WPV1 importation (Tanzania, Zambia, and Zimbabwe) responded by increasing surveillance and organizing up to six rounds of national and subnational polio supplementary immunization activities (SIAs).* Although no cases of paralytic WPV1 infection have been reported in Malawi since November 2021 or in Mozambique since August 2022, undetected transmission might be ongoing because of poliovirus surveillance gaps and testing delays. Efforts to further enhance poliovirus surveillance sensitivity, improve SIA quality, and strengthen routine immunization are needed to ensure that WPV1 transmission has been interrupted within 12 months of the first case, thereby preserving the WHO African Region's WPV-free status.

FIGURE 1

Location of wild poliovirus type 1 cases and the five outbreak response countries — southeastern Africa, 2021–2022 Abbreviation: WPV1 = wild poliovirus type 1. * Malawi, Mozambique, Tanzania, Zambia, and Zimbabwe.

FIGURE 2

Nonpolio acute flaccid paralysis rates, by district in the five outbreak response countries — southeastern Africa, 2021–2022 Abbreviation: AFP = acute flaccid paralysis. * Cases per 100,000 children and adolescents aged <15 years. ^† Malawi, Mozambique, Tanzania, Zambia, and Zimbabwe.

FIGURE 3

Bivalent oral poliovirus vaccine supplementary immunization activity quality as assessed by lot quality assurance sampling surveys, by supplementary immunization activity and district in the five outbreak response countries —southeastern Africa, 2022 Abbreviation: LQAS = lot quality assurance sampling. * Malawi, Mozambique, Tanzania, Zambia, and Zimbabwe.