Time to childhood immunization uptake in Kenya: a survival model

Abstract

Background: Childhood immunization is an important intervention aimed at reducing morbidity and mortality among under-fives. Immunization coverage is the most common indicator used to evaluate the performance of this intervention. To achieve maximum benefits in controlling vaccine preventable diseases, measuring the timeliness of vaccine uptake should be considered. A vaccine is considered untimely if it is administered outside the suitable age range based on the schedule. Children who are immunized outside the appropriate age range are susceptible to vaccine preventable diseases. Objective: To examine time to childhood immunization uptake among children aged 12 to 23 months in Kenya. Methodology: This study used Kenya Demographic Health Survey data for the year 2014. This data provides information on child details, immunization records including date of vaccine administration. The target population was of children between 12 and 23 months of age required vaccines. Categorical variables were summarized using percentages. Timeliness of vaccination was assessed using the date of vaccine administration and date of birth of child. Nonparametric Kaplan Meir method was used to estimate the cumulative vaccination coverage. The event of interest (failure) is untimely vaccine uptake and the survival time is time in months until vaccination receipt. Censored observations were those of children receiving a specific vaccine on time. Multilevel Cox regression was used to model the predictors of time to immunization uptake. Results: Full immunization coverage was estimated at 54.3%. The coverage was highest for BCG (95.8%), OPV1 (96.6%) and Pentavalent1 (96.5%). Overall, the coverage reduced over time for the three doses of OPV, Pentavalent and PCV. 28.3% of the children received vaccines on time, 47.5% received early while 24.1% had delayed vaccines. Education level, place of delivery, birth order, religion and maternal age predicted time-to-immunization uptake but differ between vaccines. Conclusion: Timeliness of vaccines was low despite the high coverage reported for the vaccines. This shows a gap in the implementation and monitoring of vaccine programs, which calls for focused efforts and strategies towards improving immunization timeliness as an indicator for effectiveness and immunization performance globally.