The Timeliness of Childhood Vaccinations in Tanzania: A Literature Review and Analysis of Demographic Health Surveys Data

Background: Routine immunization is the most effective way to prevent mortality from vaccine preventable diseases. Though vaccination coverage rates have improved over the past decade, vaccinations still fail to be delivered and received within a proper timeframe. Across low and middle income countries the median vaccination delay falls between 2.3 to 6.2 weeks for birth through third dose vaccinations [1]. Countries in the African region have 5 to 6 percent lower coverage and face lower timeliness than LMICs overall, and in Tanzania, vaccination delays reach up to 70 percent [1, 2]. This study seeks to investigate the determinants of timely vaccination delivery using two approaches. First, a review is conducted to assess the causes of delayed vaccination in Sub-Saharan Africa (SSA) and, second, an analysis of the Tanzania Demographic and Health Surveys (DHS) data provides evidence of the timeliness factors of concern. Methods: Peer-reviewed literature on vaccination coverage and timeliness in SSA was searched on several databases and was subsequently selected if it pertained to the determinants of vaccination coverage or vaccination timeliness for humans. Pharmacological interventions and vaccine efficacy research was excluded. The literature is rigorously reviewed by classification of determinants into four framework clusters (family characteristics, immunization systems, parental knowledge/ attitudes, and communication and information). The 2015 Tanzania DHS data is used to measure timely immunization. Determinants of fully timely immunization are analyzed through logistic regression. Results: The results of the literature review provided 36 papers on vaccination timeliness and 15 papers on vaccination timeliness. Family characteristics are found to be the major determinants of both vaccination coverage and timeliness appearing 29 and 6 times, respectively. The immunizations system was also found to impact vaccination coverage and vaccination timeliness with 24 and 3 appearances. Our DHS analysis supports these findings, showing statistically significant links between complete timeliness and family characteristics (maternal age, wealth quintile, maternal education, and region) and the immunization system (antenatal care visits and tetanus toxoid vaccine). Conclusions: This investigation finds several family characteristics and the immunization system as determinants of delayed vaccination delivery. Escalating the number of vaccination facilities or health facilities in underserved regions could alleviate disparities found amongst families, as these characteristics are often clustered regionally. Further, action must be taken to improve the immunization system by ensuring availability of vaccines everywhere, good vaccine management, and adequate staff. Understanding the causes of poor vaccination timeliness is crucial in efforts to improve problems and provide timely vaccination to prevent child mortality.