Informing life-course immunization and pandemic preparedness: a COVID-19 vaccine evaluation and HPV introduction experience in Sierra Leone

BACKGROUND: Sierra Leone launched its COVID-19 vaccination in March 2021 and achieved 73.2% full coverage among individuals aged 12 and older by December 2022. In October 2022, the country introduced the human papillomavirus (HPV) vaccine for 10-year-old girls, leveraging infrastructure and lessons from the COVID-19 vaccine deployment. We conducted a COVID-19 vaccine post-introduction evaluation (cPIE) to document best practices, assess impact on routine immunization, and identify key levers that supported HPV vaccine rollout, and recommendations for future pandemic preparedness. METHODS: We adapted the World Health Organization COVID-19 Post-Introduction Evaluation tool and conducted 84 structured interviews with national, district, and health facility staff in six districts, complemented by a desk review. Qualitative data were analysed thematically. RESULTS: By October 2023, COVID-19 full vaccination coverage was estimated at 86.7% among people aged ≥ 12 years, and first-dose coverage exceeded 100% based on programme denominators, likely reflecting uncertainty in population projections. Over 84% of doses were administered via surge campaigns and periodic intensification of routine immunization. Key lessons included: (1) delivering adult vaccination services closer to clients (e.g., schools, workplace, and homes); (2) re-tooling existing health infrastructure and systems; (3) engaging community leaders to build demand across the life-course; (4) strengthening electronic data systems for vaccination tracking; (5) integrating vaccines within one delivery platform; and (6) promoting operational innovations for rapid response. HPV vaccine uptake exceeded expectations, with 119% of the targeted girls vaccinated and 68% of doses administered in schools, supported by COVID-19 vaccination platforms, including cold chain, digital registries, and community mobilization networks. However, surge delivery approaches strained workforce capacity and were reported to disrupt routine immunization in some areas. CONCLUSION: Sierra Leone's experience highlights the feasibility of using emergency vaccination platforms to accelerate life-course vaccination and new vaccine introductions in low-resource settings. Sustained preparedness will require earlier integration guidance, strengthened coordination, financing, and improved data systems to support adult and adolescent immunization alongside routine services.