The results of this study have shown that half of the HAs of the Mont Ngafula II HD recorded high dropout rates.
More than two-fifth of them also registered low vaccine coverage while only one HA reported exclusively low vaccine coverage.
Concerning the predictors, residing in rural areas and the absence of immunization card, no seating places and no respect of the order of arrival during vaccination in health facilities as well as the lack of a reminder system on days before the scheduled vaccination were significantly associated with high dropout rates among children aged 12–23 months.
Concerning the local system of vaccination services, the poor utilization of vaccine services seemed as the main health concern followed by the poor access at HA scale. Among the HAs that recorded high dropout rates, more than half reported good access but poor utilization of vaccination services (high vaccine coverage and high dropout) while two-fifth registered both poor access and poor utilization vaccination services (low vaccine coverage and high dropout). Furthermore, only one HA reported both poor access and high utilization vaccination services (low vaccine coverage and low dropout). Thus, these results may represent a useful indicator for the risk assessment of vaccination services in the study area.
In the present study, children without immunization card had higher susceptibility to drop out from vaccination services. Not having an immunization card was also found as a predictor of incomplete immunization in other studies from low-income African countries (15, 17, 18). This situation may be related to perception of attitudes of the health staff. As suggested by Baguune et al. (2017), in case of loss of immunization cards, negative attitudes from some health workers unable to provide new vaccination cards induce a reluctance feeling of mothers for new vaccination in health facilities (15). This evidence is also supported by the results from a cross-sectional survey conducted during a polio outbreak in Cameroon in which good perception of immunization services was considered as a determinant of vaccination completeness (19). Thus, we hypothesize that a good reception of health staff can strengthen interpersonal communication and be a major asset for the subsequent use of the immunization services.
This study showed that children residing in rural areas were more likely to drop out compared to their urban counterparts. However, discordant results have been reported in other studies, especially conducted in Asia and Africa. At the contextual level, living in rural areas was associated with breaks in childhood vaccination in India (20) while this characteristic was found protective in a multilevel analysis involving 24 African countries (21). As suggested previously, discrepancies observed would call into question the urban advantage probably due to urban demographic growth and related difficulties of access to health services (20, 22–24).
Respondents perceived that unavailability of seating places and no respect of the order of arrival during vaccination in health facilities were associated with immunization dropout rate. In addition, the lack of a reminder system on days before the scheduled vaccination was also perceived as a predictor to high dropout. This result is similar to studies conducted by Bangure et al. (2015) in Zimbabwe (25), Haji et al. (2016) and Gibson et al. (2017) in Kenya (26, 27). They found that complete immunization was significantly higher among children of mothers/caregivers who received short message service (SMS) reminders than those in control groups. Thus, our findings support the hypothesis that implementing and extending a reminder system using SMS-type messages may contribute to improve substantially immunization services in our context.
Other socio-demographic characteristics considered in the present study were not statistically associated with dropout rate while they were found as predictors of incomplete vaccination. Children (birth order, sex), parents (education level, religion), and household (number of children) characteristics were significantly related to the children immunization status in several African studies (15, 19, 26, 28–34). Growing number of children, sex discrimination, low parents’ education level, and misconceptions from certain religious groups affecting vaccination uptake may lead to immunization dropout (15, 19, 26). The discrepancies observed on these characteristics in our study represent the first limit. They could be explained by our small sample size and some specifics characterizing the objectives assigned and the sample procedures comparatively to other studies.
A second study limitation is that determinants of vaccination dropout rates were assessed from the perspective of the users of vaccination services. Evaluation from the perspective of health systems and providers was not considered. However, determinants of childhood immunization coverage are complex and interrelated. Vaccination depends on a real need for vaccines and health seeking service from users and high-quality service of vaccines offer under the optimal technical, logistical, and operational conditions from providers (35).
Nonetheless, there has been a limited number of research in DRC concerning vaccination dropout (36). To our knowledge, the present study is the first conducted at both fine spatial scale and individual level to understand the main health concern of vaccine services and identify factors related to low vaccination completeness among children aged 12–23 months. An additional strength of this survey is that the result of this study can be extrapolated to the population of the DRC because the survey used a probability sampling technique and the minimum sample size was computed taking into account the formula required to allow each person to be part of the sample.