Completion of multi-dose COVID-19 vaccines and the associated factors among adolescents and adults in two urban informal settlements in Nairobi, Kenya

Completion of vaccine doses is essential for robust immunity and long-term protection against specific diseases. This study aimed to investigate factors associated with the completion of multi-dose COVID-19 vaccines (MDV) among adolescents and adults in two informal urban settlements in Nairobi, Kenya. We analyzed data from the Kenya Multisite Integrated Serosurveillance (KEMIS) project. We defined completion of MDV as receiving an additional COVID-19 vaccine dose between weeks 6 and 8 following the first COVID-19 vaccination shot. We applied the modified Poisson regression model with robust standard errors to determine the factors that were independently associated with the completion of MDV. We analyzed data from 402 individuals aged 14-90 years and found that the completion rate for MDV was 85.3%. In the adjusted analysis, participants aged ≥60 years (adjusted prevalence risk ratio [aPR] 1.30, 95% confidence interval [CI] 1.05-1.60) and those who recommended the COVID-19 vaccine to others (aPR 1.40, 95% CI 1.00-1.96) were significantly more likely to complete MDV. Individuals aged 25-59 years (aPR 1.22, 95% CI 0.99-1.50), those who perceived themselves as being at risk for COVID-19 (aPR 1.09, 95% CI 0.99-1.19), and those who had access to healthcare during the pandemic tended to have a higher completion of MDV. Overall, the MDV completion rate is relatively high, however, public health interventions should endeavor to target those being left behind such as younger individuals and those hesitant about vaccination.