The association between routine immunisation and COVID-19 vaccination in small Island developing states

Objectives: Understanding the link between routine immunisation (RI) performance and vaccination during an epidemic can provide insights on health systems resilience and investments to strengthen health systems. We examined the relationship between RI performance and COVID-19 vaccination coverage in small island developing states (SIDS). 

Methods: We analysed immunisation and health system performance data in 55 SIDS. Our primary outcome was COVID-19 vaccination coverage at four timepoints (June 2021, December 2021, June 2022 and December 2022). We examined associations with coverage of six childhood immunisations (5-year mean annual coverage for 2015–2019), pandemic-related disruptions to RI, new vaccine introductions, health system performance measures, and economic and demographic characteristics. We calculated Spearman correlation coefficients (r) with p-values (p<0.05 considered significant) and 95% confidence intervals for continuous variables and mean COVID-19 vaccination coverage by categorical variables. 

Findings: COVID-19 vaccination coverage was higher in countries that sustained pre-pandemic RI coverage during the pandemic, and where HPV, influenza and measles-containing (second dose) vaccines had been introduced. There were weak correlations (|r|<0.4) between coverage of COVID-19 vaccination and RI, with a few exceptions of moderate correlations with the birth dose of hepatitis B vaccine (June 2022: r=0.421, p=0.007; December 2022: r=0.438, p=0.005) and first dose of measles vaccine (December 2021: r=0.420, p=0.002). COVID-19 vaccination coverage was strongly correlated with the density of physicians (June 2021: 0.897, p<0.001; December 2021: 0.785, p<0.001) and moderately correlated with that of nurses and midwives (June 2021: 0.630, p=0.001; December 2021: 0.605, p=0.002). COVID-19 vaccination coverage was lower in SIDS with lower country income and development status. 

Conclusions: Countries that achieved high COVID-19 vaccination coverage also sustained RI coverage during the pandemic, demonstrating health system resilience. Our findings highlight the importance of having sufficient skilled health professionals and experience in introducing new vaccines targeting different age groups into national programs, particularly in small island settings.