*3.3. Factors Associated with Zero-Dose Vaccine in Children Aged 12 to 23 Months in the DRC*

After adjusting for independent variables, being zero-dose was significantly associated with the age of the mother or guardian being less than or equal to 19 years (AOR = 1.23 (95% CI 1.06 to 1.44)); maternal education (lack of education AOR = 3.46 (95% CI 1.99 to 5.99), primary AOR = 3.14 (95% CI 1.81 to 5.42), and secondary level AOR = 3.87 (95% CI 2.22 to 6.75) compared to the level of higher or university education); religious affiliation (willful failure to disclose religious affiliation AOR = 4.22 (95% CI 1.63 to 10.94), Muslim AOR = 1.71 (95% CI 1.25 to 2.33), revival/independent Church AOR = 1.35 (95% CI 1.22 to 1.50), Kimbanguist AOR = 1.31 (95% CI 1.03 to 1.66), and Protestant AOR = 1.12 (95% CI 1.01 to 1.25) compared to the Catholic); proxies for wealth such as not having a telephone to use AOR = 1.59 (95% CI 1.45 to 1.75) or a radio AOR = 1.48 (95% CI 1.34 to 1.63); and lack of civil registration AOR =2.04 (95% CI 1.81 to 2.24). Parents who reported having to pay for a vaccination card or for another immunization-related service were more likely to have a ZD child AOR =2.02 (95% CI 1.81 to 2.24) and AOR =3.22 (95% CI 2.57 to 4.03), respectively. Finally, not being able to name any vaccine-preventable disease (VPD) was also associated with being ZD, AOR = 3.37 (95% CI 2.94 to 3.87). Summary of these findings are in Table 2.

**Table 2.** Bivariate and multivariate analysis of the association "zero-dose" and socio-demographic, economic, communication, and system-related characteristics, 2021–2022 Vaccination Coverage Survey, DRC.



#### **Table 2.** *Cont.*

With n = number of subjects in the sample; OR = Odd Ratio; AOR = Adjusted Odd Ratio; 95% CI = 95% Confidence Interval; RA = religious affiliation.

#### **4. Discussion**

The results from this survey showed 19.1% ZD, representing between 767,061 and 775,135 ZD children in the DRC. This result is similar to the proportion estimated by WHO and UNICEF relating to the national vaccination coverage estimates of 19% for the DRC in 2021 [6]. The fact that almost 1 in 5 children aged 12 to 23 months was ZD in the DRC in 2021 is high in comparison to other low- and low-middle-income countries including those in Africa [2]. There was an increase in the prevalence of zero-dose children in sub-Saharan Africa from 6.8% in 2010 to 14% during the COVID-19 pandemic year of 2021 [2].

Our study found that zero-dose children were significantly associated with several factors. Zero-dose children were positively associated with young mothers, which is similar to findings from several studies. The older the mother gets, the less she may hesitate and the fewer barriers she may face to have the child vaccinated [8–11]. Our study also found that uneducated mothers and those who had only primary or secondary education were more likely to have a ZD child compared to those with higher or university education. Maternal education has been associated with vaccination in most settings [12–24]. This may be affected by changes affected by education in attitudes, traditions, and beliefs, and even increased autonomy and control over household resources that would improve health-care seeking [12–20]. Zero-dose status was also associated with religious affiliation in the DRC, with those not reporting an affiliation having the highest odds of having an unvaccinated child. A pooled cross-sectional study of individual and national data obtained from Demographic and Health Surveys of 33 sub-Saharan African countries found that the children of Muslims were significantly more likely to be zero-dose than children of Christians (25.2% versus 12.3%) [25]. However, Costa et al., in an analysis of 66 low and middle income countries with standardized national surveys since 2010, found that the relationship between religion and vaccination was not consistent across the world [26]. The latter suggests that various cultural and community-level factors may modulate the relationship between religious affiliation and immunization. Working with religious leaders may be an appropriate solution.

Zero-dose children are significantly related to proxies for wealth such as not having a telephone to use or a radio. These two elements are currently important channels through which messages can pass to reach a large part of the population. This significant link somehow reflects the existence of a dissemination of messages likely to encourage parents to have their children vaccinated. However, information and communication are a major challenge in the viability of an initiative. Its success or failure depends on communication and information [27]. Vaccination services, which are the subject of so much controversy, cannot do without communication. Communicating to convince cannot be improvised either at the risk of reaping the opposite effects of what is expected. It is, therefore, worthwhile to rely on the socio-cultural realities of the populations in order to develop appropriate communication strategies, including those adapted to these two channels, to better explain the advantages of vaccination. In the DRC, ZD children were also significantly linked to the lack of civil registration. This result opens a window of action to linking immunization and birth registration, as has been discussed by many in recent years [28,29]. Another finding that is of significance is the high proportion of people reporting having to pay for a vaccination card or another immunization-related fee, as this is a potentially modifiable factor. This study suggests an inhibiting role of fees on child vaccination, and this has been reported as an important barrier elsewhere. This undoubtedly goes against the official free vaccination policy of the DRC, which is aimed at breaking down the financial barrier to give the population maximum access to vaccination services; several studies support that making vaccination free plays a most fundamental role in improving immunization coverage [30,31].

Finally, not being able to name any VPD was also associated with being zero-dose. This association has also been found in several studies conducted in sub-Saharan Africa, particularly in Ethiopia, Burkina-Faso, or Nigeria, including systematic reviews. The lower the level of knowledge, the less likely the caregiver is to vaccinate the child. Working on improving maternal and community knowledge about vaccination, about the diseases that are targeted for protection, the consequences of not vaccinating the child, the vaccination schedule, and on awareness of vaccination campaigns can help improve vaccination [8,17,21,24,32].

The literature suggests that to reduce inequalities in immunization, targeted and pro-equity interventions should be explicitly developed. Such interventions need to be multicomponent to mainly facilitate access through the proper offer of services and communitybased mobilization, outreach, and education, adapted to the language and health literacy of the population [33]. Using the results of the 2021–2022 Vaccination Coverage Survey, along with periodic monitoring of process indicators, each province, and health zone, in the DRC is tailoring its immunization delivery strategy. The survey and this analysis were conducted in the context of the Mashako Plan [5]. Alongside other system-strengthening actions, the Mashako Plan is a multipartner and multicomponent initiative that is addressing access and inequalities through simple and targeted interventions developed in collaboration with many stakeholders. The Plan started targeting 9 provinces and has now been extended to all but two of the provinces. It took lessons from previous experiences, including work to improve coverage in Kinshasa [34]. The focus is to favor access to vaccination by strengthening local-level data use and accountability for better micro-planning, outreach, and reduction of vaccine stock-outs, supportive supervision and outreach monitoring, as well as demand generation through community engagement [5].

#### *Limitations*

This study reflects one point in time, and it does not provide longitudinal data. It relies on survey data that can be affected by selection and information biases. The sampling frame was derived from 1984 census data that is known to be inaccurate. To tackle this issue, a household listing exercise was conducted in all selected clusters. Only 7 of 519 health zones were excluded due to insecurity and non-response was 0.3%, with 86920 HHs participating out of 87166 selected HHs. Yet, communities not included in the sampling frame may have been left out and such communities may also be less likely to be reached with vaccines. Vaccination history obtained from cards or facility records may have errors, as records

can be incomplete or difficult to read or interpret [35,36]. Additionally, the proportion of vaccination status ascertained by recall was 30%, which can lead to recall bias; although, stating that a child was not vaccinated might be more accurate than indicating which vaccines or how many doses a child has received [37]. Similarly, the ascertainment of factors that relate to vaccination might also suffer from desirability or other biases that are difficult to quantify. Finally, while we assessed factors that were related to being ZD, our study did not go into root cause analysis of the actual reasons for not being vaccinated, or even the factors related to the provision of vaccination services that may affect vaccination.

### **5. Conclusions**

Zero-dose is frequent and contributes to the serious health problems in the Democratic Republic of the Congo, with some provinces having over half of their children unvaccinated. Important geographic, demographic, and socio-economic inequalities were observed and quantified. Several factors were associated with not being vaccinated; yet, only better understanding of the underlying causes of ZD will help to inform strategic and operational decisions and to tailor interventions aiming at reducing the ZD burden. Inequalities in immunization should continue to be monitored to assess progress.

**Author Contributions:** Conceptualization, D.K.I., M.M.N., M.C.D.-H., E.M., P.S.L.D. and A.L.; methodology, D.K.I., M.M.N., E.M., P.S.L.D. and A.L.; formal analysis, D.K.I. and M.M.N.; investigation, E.M., P.S.L.D. and A.L.; writing—original draft preparation, D.K.I., M.M.N. and M.C.D.-H.; writing—review and editing, D.K.I., M.M.N., M.C.D.-H., E.M., P.S.L.D., A.L., J.-C.M., M.D.Y., C.M., G.F.N., R.B.R., F.-F.M., A.M.-W.C., C.L.L., D.M. (Dieudonné Mwamba), C.N., D.M. (Deo Manirakiza) and J.O. All authors have read and agreed to the published version of the manuscript.

**Funding:** The survey that generated the data used in this study was funded by the United Nations Children Emergency Funds (UNICEF) after mobilizing a significant funding from GAVI. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

**Institutional Review Board Statement:** The study protocol was approved by the institutional review board of the Kinshasa School of Public Health Ethical committee (n◦ ESP/CE/175/2021). This study was conducted in accordance with the Helsinki Declaration II. Authorization was also provided by health and politico-administrative authorities.

**Informed Consent Statement:** Verbal informed consent was obtained from all subjects involved in the study. The research team provided the respondent with information about the nature of the study, its objectives, the risks and benefits incurred, and the freedom to participate or not without any prejudice.

**Data Availability Statement:** The data presented in this study are available on request from the WHO-DRC office at the email address "nimpamengouom@who.int". The data are not publicly available due to the sensitivity of certain information from health facilities.

**Acknowledgments:** We are very thankful to the team of research nurses and physicians for their involvement in the collection of data used in this study. We are also very grateful for the direction of the Kinshasa School of Public Health for their flexibility in collaboration during the survey and to Dale RHODA for advice on the statistical methods used.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
