This study investigates the effectiveness of postnatal support services provided to HIV-positive mothers in Nairobi, Kenya, with a focus on their impact on infant immunization rates. A community-based intervention approach was employed, including structured support groups, home visits by healthcare providers, and educational workshops. Data collection utilised a mixed-methods design combining quantitative surveys with qualitative interviews. Among the study participants, there was an observed increase in infant immunization rates from 75% to 82%, indicating a positive trend towards improved health outcomes for HIV-positive mothers' children. The findings suggest that targeted postnatal support services can significantly enhance adherence to pediatric vaccination schedules among HIV-positive mothers in Nairobi, Kenya. Further research should explore the sustainability of these interventions and their scalability across different socio-economic contexts. HIV-positive mothers, Postnatal care, Infant immunization rates, Community-based intervention Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.