Childhood vaccination coverages in rural Guinea-Bissau before and during the early COVID-19 pandemic, a cohort study

Background: The COVID-19 pandemic response diverted health systems resources to COVID-19 activities. Modelling studies and estimates based on administrative data indicate that the number of un- and undervaccinated children increased during the pandemic, especially in the world's poorest countries. We investigated vaccination coverage and timeliness among children born in rural Guinea-Bissau before and during the pandemic. Methods: Utilizing Bandim Health Project's nationally representative rural Health and Demographic Surveillance System, 12-month vaccination coverages and vaccination timeliness were assessed for all scheduled vaccines among children born in 2017 and 2020. Furthermore, proportions of fully-immunized children and out-ofsequence Bacillus Calmette-Gue<acute accent>rin vaccine (BCG) and measles vaccine (MV) were assessed. Associations between background factors and coverages/out-of-sequence vaccinations were analysed for BCG, Pentavalent vaccine dose 3 (Penta3), and MV using mixed-effects logistic regression models with random effects for village cluster and health area. Results: A total of 6809 children were included (2017: 3495, 2020: 3314). Coverage estimates ranged from 19 % to 99 % in the 2017 cohort and 40 % to 98 % in the 2020 cohort. Only BCG and oral polio vaccine, which were affected by stock-outs, had markedly lower 12-month coverages in the 2020 cohort compared with the 2017 cohort. When excluding vaccines affected by stock-outs, there was no difference in the proportions of fully-immunized children estimates between the two cohorts (66 % and 67 %). Delays were common but timeliness improved from 2017 to 2020 for all vaccines except BCG. Out-of-sequence BCG vaccinations were markedly more prevalent in the 2020 cohort (48 %) than in the 2017 cohort (27 %) while out-of-sequence MV vaccinations were similar across the cohorts. Conclusion: There are no indications that the pandemic substantially changed vaccination patterns. Changes in vaccination coverages were likely driven by stock-outs rather than changes in vaccination services or health system access/demand and were not reflected in timeliness of vaccination.