Persistent Transmission of Circulating Vaccine-Derived Poliovirus - Somalia, January 2017-March 2024

Area of Science:

• Public Health
• Infectious Diseases
• Vaccinology

Background:

• Global Polio Eradication Initiative has significantly reduced wild poliovirus (WPV) transmission.
• Withdrawal of oral poliovirus vaccine type 2 (OPV2) in 2016 led to circulating vaccine-derived poliovirus type 2 (cVDPV2) outbreaks globally.
• Somalia has experienced ongoing cVDPV2 transmission since 2017, with cases spreading to neighboring countries.

Purpose of the Study:

• To review polio vaccination coverage and surveillance data in Somalia.
• To assess the factors contributing to persistent cVDPV2 transmission.
• To identify strategies for interrupting cVDPV2 transmission.

Main Methods:

• Analysis of cVDPV2 case data from January 2017 to March 2024.
• Review of supplementary immunization activities (SIAs) conducted since January 2021.
• Assessment of vaccination status among children with nonpolio acute flaccid paralysis.

Main Results:

• 39 cVDPV2 cases detected in 14 of 20 Somali regions between January 2017 and March 2024.
• Transmission has extended to Ethiopia and Kenya.
• 12% of children with nonpolio acute flaccid paralysis had not received OPV doses, with most in inaccessible South-Central regions.

Conclusions:

• Persistent cVDPV2 transmission in Somalia is linked to low population immunity and challenges in accessing security-compromised areas.
• Enhancing humanitarian negotiations to allow vaccination in inaccessible districts is vital.
• Improving the quality of vaccination campaigns in accessible areas is necessary to interrupt cVDPV2 transmission.