Optimizing decision-making, implementation, and monitoring to maximize the impact of the transition from pentavalent + IPV to hexavalent vaccine in Mauritania

Background On July 1, 2025, with support from Gavi, the Vaccine Alliance, Mauritania became one of the first countries in Africa to switch from pentavalent (DTP–HepB–Hib) plus inactivated poliovirus vaccine (IPV) to a single hexavalent vaccine (DTwP–HepB–Hib–IPV). Aims This study evaluated the preparation for and early implementation of Mauritania's hexavalent vaccine switch, generating real-world evidence and practical lessons learned to inform other Gavi-supported countries considering a similar transition. Methods National pre- and post-introduction assessments were conducted between April and June 2025 and July and September 2025, respectively. Using a mixed-methods design aligned with the WHO Post-Introduction Evaluation framework, data were collected across seven regions through reviews of administrative data from DHIS2, health facility and household surveys, parent/caregiver focus group discussions, and key informant interviews. The assessment examined cold chain and logistics, health worker training, data systems, adverse events following immunization (AEFI) surveillance, community acceptance, vaccination coverage trends, and preliminary costs associated with the switch. Results Political commitment, community acceptance, and a functional cold chain system supported successful rollout. During the first three months following introduction, estimated coverage reached 81% for the first hexavalent dose and 68% for the third dose. Key operational challenges included uneven dissemination of vaccine-introduction tools, limited functionality of monitoring and evaluation systems, and gaps in health worker training. Findings also identified existing structural barriers to accessing vaccination services, particularly in rural areas. Conclusions Mauritania's early experience demonstrates that strong political commitment, community acceptance, and adequate cold chain capacity supported their successful hexavalent switch. However, sustained investments in health worker training, monitoring and evaluation, implementation tools, and equitable access to vaccination services are needed to strengthen implementation and coverage. These findings offer practical lessons for other countries transitioning from pentavalent plus IPV to hexavalent vaccines.