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

Area of Science:

• Epidemiology
• Virology
• Public Health

Background:

• The Global Polio Eradication Initiative (GPEI) has significantly reduced wild poliovirus (WPV) cases globally since 1988.
• The World Health Organization (WHO) African Region was certified free of indigenous WPV in August 2020.
• Wild poliovirus type 1 (WPV1) remains endemic only in Afghanistan and Pakistan.

Purpose of the Study:

• To report on the progress of the WPV1 outbreak response in southeastern Africa.
• To summarize findings from WPV1 cases identified in Malawi and Mozambique.
• To highlight the public health response and ongoing challenges in interrupting WPV1 transmission.

Main Methods:

• Genomic sequence analysis to trace the origin of the WPV1 outbreak.
• Surveillance for paralytic polio cases in Malawi, Mozambique, and high-risk neighboring countries.
• Implementation of up to six rounds of national and subnational polio supplementary immunization activities (SIAs).

Main Results:

• Nine WPV1 paralytic polio cases were identified in southeastern Africa between November 2021 and December 2022 (one in Malawi, eight in Mozambique).
• Genomic analysis confirmed the WPV1 strain originated in Pakistan.
• Response efforts included increased surveillance and SIAs in Malawi, Mozambique, Tanzania, Zambia, and Zimbabwe.

Conclusions:

• Despite no reported cases since August 2022 in Mozambique, undetected WPV1 transmission may persist due to surveillance gaps.
• Enhanced poliovirus surveillance sensitivity and improved SIA quality are critical for interrupting WPV1 transmission.
• Sustained efforts are necessary to preserve the WHO African Region's WPV-free status and achieve global polio eradication.