Abstract
Background
In Ethiopia, despite national immunisation programmes, many children do not complete recommended vaccines. Identifying determinants of incomplete immunisation is crucial for designing interventions and guiding policy. This study explored factors associated with incomplete immunisation among children aged 12–23 months in Koore Zone, Southern Ethiopia.
Methods
A community-based unmatched case-control study was conducted from April to May 2025, including 279 children—93 incompletely immunised cases and 186 fully immunised controls randomly selected from 10 kebeles. Structured, interviewer-administered questionnaires adapted from WHO and United Nations Children’s Fund tools collected data on sociodemographics, maternal healthcare utilisation and caregiver knowledge. Descriptive statistics summarised participant characteristics. Bivariable and multivariable logistic regression identified independent associated factors of incomplete immunisation, expressed as adjusted ORs (AORs) with 95% CIs.
Results
Overall, 42% of incompletely immunised children were born at home. Maternal illiteracy, rural residence and home delivery significantly increased the likelihood of incomplete immunisation (AOR 1.82, 4.0 and 2.30, respectively). Attendance at antenatal care (AOR 0.51), postnatal care (AOR 0.46) and adequate maternal knowledge of immunisation (AOR 0.30) were protective.
Conclusion
In Koore Zone, incomplete immunisation is driven by maternal education, rural residence, home delivery, maternal healthcare utilisation and caregiver knowledge. Strengthening maternal and child health services, improving community awareness and educating caregivers about vaccination schedules are vital strategies to enhance immunisation coverage and reduce vaccine-preventable diseases. These findings provide practical guidance for policy makers and public health practitioners in similar low-resource settings.
Keywords: Ethiopia, Child Health, Epidemiology
WHAT IS ALREADY KNOWN ON THIS TOPIC
In Ethiopia, many children do not complete the full course of recommended vaccines, particularly in rural and hard-to-reach areas.
Most prior studies are urban-focused or cross-sectional, limiting understanding of local factors in rural communities.
WHAT THIS STUDY ADDS
Offers context-specific insights from a rural, culturally diverse area using a case-control study design.
HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY
Supports expansion of rural outreach services and efforts to remove structural barriers to complete vaccination.
Provides evidence for future research and policy planning to reduce vaccine-preventable illness among children in low-resource settings.
Background
Childhood immunisation is widely recognised as one of the most effective and life-saving public health strategies, averting millions of deaths each year worldwide.1 The WHO recommends that children receive a full series of essential vaccines within their first year of life to protect against serious illnesses such as measles, pertussis, diphtheria and poliomyelitis.2 However, despite notable progress in global vaccine coverage, many children, especially in low- and middle-income countries, still miss critical doses or experience delays, leaving them vulnerable to preventable diseases.3 In sub-Saharan Africa, significant gaps in vaccination coverage persist, undermining herd immunity and exposing communities to recurring outbreaks.4
Ethiopia has implemented an Expanded Programme on Immunization (EPI) since 1980, achieving significant improvements in vaccine coverage.5 However, national surveys reveal that the proportion of fully immunised children remains below the WHO target of 90%, with considerable regional variation.6 In 2022, the Demographic and Health Survey reported that only 43% of Ethiopian children aged 12–23 months had received all basic vaccinations.7 The persistence of incomplete immunisation poses a challenge to achieving Sustainable Development Goal 3, which seeks to end preventable deaths of newborns and children under 5 years.8 Understanding the determinants of incomplete immunisation within different local contexts is therefore critical for designing tailored interventions and ensuring equitable access to child health services.9
Previous studies in Ethiopia and other low-income countries have highlighted several factors associated with incomplete childhood vaccination, such as maternal education, household income, place of delivery, distance to health facilities and caregivers’ knowledge or attitudes towards vaccines.10,13 Many of these studies, however, were conducted in urban or easily accessible areas, where health service coverage and sociodemographic conditions differ considerably from those in remote or pastoralist communities.14 Moreover, cross-sectional designs, commonly used in these studies, are limited in distinguishing true determinants from simple associations, making it difficult to draw causal inferences.15 To overcome these limitations, we conducted a case-control study, which allows a direct comparison between children who are fully and incompletely immunised, providing stronger evidence of independent predictors. The Koore Zone in southern Ethiopia presents a unique context, with a mix of highland and lowland populations, diverse cultural practices, geographic barriers and rural–urban disparities in health service access that may influence vaccination behaviours differently from other regions.16 Despite these challenges, there is a lack of empirical data from this zone, highlighting the need for a locally focused investigation.
Addressing these evidence gaps is vital for two reasons. First, the national immunisation strategy increasingly emphasises reaching ‘zero-dose’ and under-immunised children through local microplanning.17 Without robust, context-specific data, these strategies risk overlooking hidden determinants in geographically or culturally distinct communities. Second, incomplete immunisation is not merely a failure of service uptake; it reflects deeper structural inequities, including gender disparities, information barriers and trust in health institutions.18 A comprehensive understanding of these determinants within the Koore context can therefore inform more responsive and culturally sensitive public health interventions.
Children aged 12–23 months were deliberately selected for this study because this age group is internationally recognised as the standard population for assessing completion of routine childhood immunisation. According to the WHO and the Ethiopian EPI, all basic vaccines, including measles, are expected to be completed by the end of the first year of life.2 5 Assessing immunisation status before 12 months would therefore be premature, as many children are still within the scheduled vaccination period. Conversely, including older children may increase the risk of recall bias, migration-related misclassification and survivor bias. For these reasons, children aged 12–23 months are consistently used in Demographic and Health Surveys and global immunisation monitoring frameworks.6 7 Focusing on this age group allows for a valid and policy-relevant assessment of incomplete immunisation and avoids unnecessary duplication across different age ranges.
Therefore, this study aimed to identify the determinants of incomplete childhood immunisation among children aged 12–23 months in the Koore Zone, Southern Ethiopia, using a community-based unmatched case-control design. By exploring sociodemographic, maternal and health system factors, the study sought to generate locally relevant evidence that can guide policy makers and health programme planners in strengthening immunisation services and reducing preventable child morbidity and mortality.
Methods
Study setting
This study was conducted in Koore Zone, one of the administrative zones in Southern Ethiopia. The zone consists of two urban and 33 rural kebeles, the smallest administrative units in the country. According to the 2024 Koore Zone Health Office estimate, the total population was 212 061, of whom 32 148 were children under 5 years of age, and approximately 10 893 were between 12 and 23 months old.19 The zone has one primary hospital, seven health centres, 43 health posts and five private health facilities that provide both preventive and curative services.20 Koore Zone was selected for this study because of its persistently low routine immunisation coverage and the marked disparity between urban and rural kebeles.19 20
Study design and period
A community-based unmatched case-control study was conducted from 15 April to 20 May 2025 to identify determinants of incomplete immunisation among children aged 12–23 months. This design was chosen because it allows for the identification of multiple risk factors while efficiently controlling for confounding variables.
Study population
The source population comprised all children aged 12–23 months who had received at least one dose of any vaccine included in the Ethiopian routine immunisation schedule and were residing in Koore Zone. The study population included all eligible children from 10 randomly selected kebeles within the zone. Children who had missed at least one of the recommended vaccine doses were classified as cases, whereas those who had completed all vaccines appropriate for their age according to the national immunisation schedule were considered controls. Children were excluded if they had permanently changed residence, were still undergoing vaccination at the time of data collection or had incomplete or unverifiable vaccination records that did not allow reliable classification as a case or control. These criteria ensured that only children with clear and verifiable immunisation status were included, maintaining the validity of the study findings.
Sample size determination
The sample size was calculated using Epi Info V.7.1 based on the double population proportion formula. The sample size was calculated using Epi Info V.7.1 based on the double population proportion formula for an unmatched case-control study. Proportions for several key determinant variables were obtained from previously published Ethiopian studies on childhood immunisation.21 22 For each determinant, the required sample size was estimated, and the variable yielding the largest size, maternal educational status, was selected to ensure adequate power. Because the study employed a two-stage cluster sampling design (random selection of kebeles followed by proportional selection of children within each kebele), a conservative design effect of 1.5 was applied to account for intracluster correlation. Using the proportions of illiterate mothers or caregivers (22.9% among cases and 9.4% among controls), with a 95% confidence level, 80% statistical power and a case-to-control ratio of 1:2, the initially calculated sample size was 186. After applying the design effect and including a 10% allowance for non-response, the final sample size was 279 children, comprising 93 cases and 186 controls.
Sampling technique and procedures
A two-stage sampling approach was used. In the first stage, kebeles were selected purposively using routine immunisation dropout information extracted from EPI registers at local health posts. Kebeles with comparatively higher dropout rates were deliberately prioritised to ensure adequate identification of children at risk of incomplete immunisation, which is essential for a case-control study design.
In the second stage, eligible children within each selected kebele were chosen using simple random sampling. Updated household lists of children aged 12–23 months were compiled and cross-checked through house-to-house visits conducted by trained data collectors in close collaboration with health extension workers. Separate sampling frames were prepared for cases and controls, and the required sample size was allocated proportionally to each kebele based on the number of eligible children. Individual children were then selected at random from each frame until the predetermined numbers of cases and controls were reached.
Although kebeles were not selected randomly, random selection was rigorously applied at the individual level. As the primary aim of the study was to examine associations between potential determinants and incomplete immunisation rather than to estimate population prevalence, this sampling strategy was considered methodologically appropriate and unlikely to introduce meaningful bias in effect estimation.
Proportional allocation to kebeles
The total sample was distributed proportionally to the number of eligible children in each selected kebele. The number of participants per kebele was determined using a proportional allocation formula based on the population size. This procedure ensured that kebeles with larger populations contributed proportionally more participants, maintaining representativeness across the study area.
Variables of the study
The dependent variable was incomplete immunisation among children aged 12–23 months. We examined a range of independent variables that could influence childhood immunisation status, grouped into sociodemographic, maternal healthcare, behavioural and health system factors.
Sociodemographic factors included the child’s age (12–17 months or 18–23 months) and sex (male or female), as well as maternal and household characteristics. Maternal education was originally collected in four categories: illiterate, read and write, elementary and diploma or above. For transparency, table 1 presents the full distribution. However, for analysis and reporting, these categories were merged into two levels—‘illiterate’ versus ‘literate’—to improve interpretability and emphasise public health relevance. This approach ensures clarity while retaining meaningful insight into the association between maternal education and incomplete childhood immunisation. Place of residence was categorised as urban or rural, maternal occupation as employed or housewife, household monthly income as <5000 ETB or ≥5000 ETB and family size as fewer than five members or five and above. These variables were selected based on prior literature suggesting their influence on vaccination uptake.
Table 1. Sociodemographic and obstetric characteristics of children and mothers/caregivers on determinants of incomplete immunisation among children aged 12–23 months in Koore Zone, Southern Ethiopia, 2025 (n=279).
| Variable | Categorise | Cases (%) | Controls (%) |
|---|---|---|---|
| Child characteristics | |||
| Child sex | Male | 40 (43.0) | 75 (40.3) |
| Female | 53 (57.0) | 111 (59.7) | |
| Child age in months | 12–17 | 40 (43.0) | 85 (45.7) |
| 18–23 | 53 (57.0) | 101 (54.3) | |
| Maternal/caregiver characteristics | |||
| Maternal age (years) | <20 | 5 (5.3) | 14 (7.5) |
| 20–26 | 19 (20.4) | 38 (20.1) | |
| 26–34 | 51 (55.0) | 106 (56.9) | |
| 34–40 | 14 (15.0) | 25 (13.4) | |
| >40 | 4 (4.3) | 3 (1.6) | |
| Place of residence | Urban | 15 (16.2) | 84 (45.2) |
| Rural | 78 (83.8) | 102 (54.8) | |
| Occupational status | Housewives | 58 (62.3) | 122 (65.6) |
| Employed | 35 (37.6) | 64 (34.4) | |
| Educational status | Illiterate | 44 (47.3) | 65 (34.9) |
| Read and write | 37 (39.7) | 50 (26.8) | |
| Elementary | 12 (13.0) | 41 (22.0) | |
| Diploma and above | 0 (0.0) | 30 (16.1) | |
| Family monthly income (ETB) | <5000 | 75 (80.6) | 135 (72.5) |
| ≥5000 | 18 (19.4) | 51 (27.5) | |
| Birthplace of child | Home | 51 (54.8) | 78 (42.0) |
| Health institution | 42 (45.2) | 108 (58) | |
| Family size | <5 | 54 (58.0) | 118 (63.5) |
| ≥5 | 39 (42.0) | 68 (36.5) | |
| Antenatal care follow-up | Yes | 31 (33.0) | 104 (56.0) |
| Maternal knowledge | Satisfactory | 29 (31.0) | 104 (56.0) |
| Poor | 64 (69.0) | 82 (44.0) | |
| Postnatal follow-up | Yes | 38 (41.0) | 107 (58.0) |
| Availability of vaccines | Yes | 15 (16.0) | 183 (98.0) |
| Fear of side effects | Yes | 38 (41.0) | 0 (0.0) |
| Accessibility to services | Yes | 4 (4.3) | 183 (98.4) |
| Possession of vaccination card | Yes | 45 (48.0) | 82 (44.0) |
ETB, Ethiopian birr.
Maternal healthcare utilisation factors included antenatal care (ANC) and postnatal care (PNC) attendance, both recorded as yes if the mother attended at least one visit during the relevant period and no if she did not. The place of delivery was classified as a home or health facility. These factors reflect opportunities for mothers to receive health education and linkage to routine immunisation services.
Behavioural factors encompassed maternal knowledge of immunisation and fear of vaccine side effects. Maternal knowledge was assessed through a 16-item questionnaire covering the importance, schedule and benefits of vaccination. Scores equal to or above the mean were considered satisfactory, while scores below the mean were considered poor. Caregivers were also asked whether concerns about side effects influenced their decision to vaccinate, recorded as yes or no.
Health system-related factors included vaccine availability at the local health post and accessibility of vaccination services, assessed through caregiver report and verification at the health facility. Both were recorded as yes or no, indicating whether structural barriers might contribute to incomplete immunisation.
This detailed operationalisation ensured that all independent variables were clearly defined, measurable and consistent with international immunisation assessment guidelines, allowing robust identification of determinants of incomplete childhood immunisation.
A child aged 12–23 months who had missed at least one of the vaccines recommended in the Ethiopian routine childhood immunisation schedule was classified as a case (partially vaccinated). The vaccines include BCG (one dose), pentavalent vaccine (DPT-HepB-Hib, three doses), pneumococcal conjugate vaccine (PCV, three doses), rotavirus vaccine (two doses), oral polio vaccine (three doses) and measles-containing vaccine (two doses). A child of the same age who had received all these vaccines according to the national schedule by 12 months of age was considered a control (fully vaccinated).
The primary caretaker was defined as the mother or caregiver primarily responsible for the child’s care and immunisation. Maternal knowledge of immunisation was assessed using 16 knowledge-related questions. Respondents scoring above the mean were classified as having satisfactory knowledge, while those scoring below the mean were classified as having poor knowledge. Categorical independent variables were grouped based on prior literature and local context. For example, maternal education was categorised as ‘illiterate’ versus ‘literate’; residence was classified as ‘urban’ or ‘rural’; ANC and PNC attendance as ‘yes’ or ‘no’. Continuous variables, such as maternal age and household income, were categorised using meaningful cut-offs informed by the study population and previous research.
Data collection tools and procedures
Data were collected using a structured, interviewer-administered questionnaire adapted from WHO and United Nations Children’s Fund immunisation assessment tools.23 24 The questionnaire was first prepared in English, translated into Amharic and then back-translated into English to ensure semantic consistency (online supplemental file 1). A pretest was conducted on 5% of the total sample in kebeles outside the study area, and the tool was refined based on the findings to improve clarity and reliability.
Data were collected electronically using the KoBo Toolbox mobile app by five trained data collectors under the supervision of two experienced public health professionals. Interviews were conducted at participants’ homes, and each child’s vaccination status was verified using immunisation cards. In cases where cards were unavailable, the information was confirmed through caregiver recall.
Data quality assurance
To ensure the quality of data, data collectors and supervisors received a 1-day intensive training session covering the study objectives, ethical principles, interview techniques and daily data verification procedures. Completed questionnaires were reviewed each day by the supervisors to check for completeness, accuracy and internal consistency. The principal investigator oversaw the overall data collection process and provided immediate feedback whenever discrepancies or inconsistencies were identified.
Data processing and analysis
Completed data were exported from KoBo Toolbox to SPSS V.25 for analysis. Descriptive statistics were computed to summarise the sociodemographic and other relevant characteristics of participants. All independent variables, as detailed in the variables section, were initially explored in bivariable analyses and subsequently included in the multivariable logistic regression model based on theoretical relevance, prior evidence and plausible causal relationships, ensuring that the key determinants of incomplete immunisation were identified in a manner that is both statistically rigorous and meaningful for public health interpretation.
We developed the multivariable logistic regression model to identify independent determinants of incomplete immunisation based on theoretical relevance, evidence from prior literature and known causal pathways. Variables were selected for inclusion in the multivariable model based on their p values from bivariable analysis, established importance in the literature and plausible relationship with immunisation outcomes (figure 1). The final model included all variables considered theoretically relevant and potentially confounding, ensuring a robust estimation of associations with incomplete immunisation. Before fitting the multivariable model, diagnostic checks were performed. Multicollinearity among independent variables was assessed using the variance inflation factor (VIF), with VIF values below 5 indicating no significant collinearity effect on outcomes. Adjusted ORs (AORs) with 95% CIs were calculated, and model fit was assessed using the Hosmer–Lemeshow goodness-of-fit test. In addition to the primary binary logistic regression analysis, a sensitivity analysis was conducted to assess the robustness of the findings using a count-based outcome. The number of missed vaccine doses for each child was treated as a count variable and analysed using multilevel Poisson regression. This model was selected because the outcome variable represented non-negative integer counts, and preliminary assessment indicated no substantial overdispersion, with the mean and variance of missed doses being comparable. The same set of independent variables included in the multivariable logistic regression model was entered into the Poisson model. Results were reported as incidence rate ratios with corresponding 95% CIs. Consistency in both the direction and statistical significance of associations across modelling approaches was used to support the robustness of the primary findings.
Figure 1. Shows conceptual framework on incomplete immunisation, Koore Zone, Southern Ethiopia, 2025.
Patient and public involvement
Patients or the public were not involved in the design, conduct, reporting or dissemination plans of this research.
Results
Sociodemographic characteristics
A total of 279 mothers/caregivers participated in the study, yielding a response rate of 100.0%. Most mothers in both groups were aged 26–34 years, with 51 (55.0%) of mothers of cases and 99 (53.2%) of mothers of controls within this age range. Among children included in the study, females predominated in both groups, accounting for 53 (57.0%) of cases and 111 (59.7%) of controls, while males constituted 40 (43.0%) of cases and 75 (40.3%) of controls. Regarding maternal education, 44 (47.3%) of mothers of cases and 65 (34.9%) of mothers of controls were illiterate or had no formal education. Most mothers were housewives, with 58 (62.0%) of cases and 122 (66.0%) of controls in this category. Most households (172, 61.6%) had fewer than five family members. Among the study participants, 45 (48%) of cases and 82 (44%) of controls had a vaccination card, and most births (150, 53.7%) occurred in health institutions. Concerning residence, 181 (65.0%) of participants lived in rural areas (table 1).
Knowledge of mothers/caregivers about child immunisation
Awareness of childhood immunisation and vaccine-preventable diseases was high among mothers/caregivers, with 89 (96.0%) of mothers of cases and 182 (98.0%) of mothers of controls reporting that they had heard about immunisation. However, only 39 (42.0%) of mothers of cases and 68 (37.0%) of mothers of controls could correctly identify five or more vaccine-preventable diseases. Maternal knowledge regarding childhood immunisation was assessed using a 16-item questionnaire (total obtainable score=16). The mean score among respondents was 9.2 (SD=3.1). Mothers/caregivers scoring ≥10 points were classified as having satisfactory knowledge, while those scoring <10 points were classified as having poor knowledge.
Regarding specific aspects of immunisation, 36 (39.0%) of mothers of cases and 89 (48.0%) of mothers of controls correctly reported the recommended age for initiating immunisation, while 74 (79.5%) of mothers of cases and 137 (74.0%) of mothers of controls were aware of the recommended age for completing the full immunisation schedule. Awareness of the total number of sessions required to complete child immunisation was reported by 34 (36.6%) of mothers of cases and 95 (51.0%) of mothers of controls. Overall, 29 (31.0%) of mothers of cases and 104 (56.0%) of mothers of controls were classified as having satisfactory knowledge of childhood immunisation.
Descriptive reasons for incomplete immunisation
Respondents reported several reasons for incomplete immunisation. Vaccine safety concerns or fear of side effects were mentioned by 38 (41.0%) of mothers of cases. A lack of awareness about the importance of immunisation was mentioned by 35 (37.8%) of mothers of cases, financial constraints by 17 (18.0%) and difficulties accessing health services by 3 (3.2%) of mothers of cases (figure 2).
Figure 2. Risk factors for incomplete immunisations of children among respondents in Koore Zone, Southern Ethiopia, 2025.
Table 2 shows the proportion of children who received each recommended vaccine. Among cases, coverage was highest for BCG and Pentavalent 1 (80%–83%) and lowest for the third doses of pentavalent, polio, PCV and measles (62%–66%), highlighting gaps in completing the immunisation schedule. All controls had 100% coverage for each vaccine.
Table 2. Proportion of children who received recommended vaccines among children aged 12–23 months in Koore Zone, Southern Ethiopia, 2025 (n=279).
| Vaccine | Cases (%) | Controls (%) | Total (%) |
|---|---|---|---|
| BCG | 75 (80.0) | 186 (100) | 261 (93.5) |
| Pentavalent 1 | 78 (83.0) | 186 (100) | 264 (94.6) |
| Pentavalent 2 | 70 (74.5) | 186 (100) | 256 (91.8) |
| Pentavalent 3 | 62 (66.0) | 186 (100) | 248 (88.9) |
| Polio 0 | 68 (72.5) | 186 (100) | 254 (91.0) |
| Polio 1 | 74 (79.0) | 186 (100) | 260 (93.2) |
| Polio 2 | 66 (70.0) | 186 (100) | 252 (90.3) |
| Polio 3 | 60 (63.8) | 186 (100) | 246 (88.2) |
| Measles | 58 (61.7) | 186 (100) | 244 (87.5) |
| PCV 1 | 72 (76.5) | 186 (100) | 258 (92.5) |
| PCV 2 | 66 (70.0) | 186 (100) | 252 (90.3) |
| PCV 3 | 60 (63.8) | 186 (100) | 246 (88.2) |
| Rota 1 | 70 (74.5) | 186 (100) | 256 (91.8) |
| Rota 2 | 62 (66.0) | 186 (100) | 248 (88.9) |
PCV, pneumococcal conjugate vaccine.
Factors associated with incomplete immunisation
In the bivariable analysis, several variables were identified as candidates for multivariable logistic regression based on a theoretical relevance, evidence from prior literature and known causal pathways. These included family size, maternal educational status, place of residence, birthplace of the child, ANC visit, monthly household income, PNC follow-up and caregiver knowledge.
After adjusting for potential confounders in the multivariable logistic regression model, six factors remained significantly associated with incomplete immunisation. Children whose mothers had no formal education were more likely to be incompletely immunised compared with children of mothers with formal education (AOR 1.82; 95% CI 1.30 to 2.50). Similarly, children from rural households had higher odds of incomplete immunisation than those from urban households (AOR 4.0; 95% CI 2.0 to 8.1). Home delivery was also associated with increased odds of incomplete immunisation compared with institutional delivery (AOR 2.30; 95% C: 1.27 to 4.1).
Attendance of ANC follow-up by the mother was associated with lower odds of incomplete immunisation (AOR 0.51; 95% CI 0.28 to 0.9), as was attendance of PNC follow-up (AOR 0.46; 95% CI 0.25 to 0.8). Mothers with satisfactory knowledge of childhood immunisation were less likely to have children with incomplete vaccination compared with mothers with poor knowledge (AOR 0.30; 95% CI 0.16 to 0.5) (table 3).
Table 3. Bivariable and multivariable logistic regression analysis of factors associated with incomplete immunisation among children aged 12–23 months in Koore Zone, Southern Ethiopia, 2025 (n=279).
| Variable | Cases (%) | Controls (%) | COR (95% CI) | P value | AOR (95% CI) | P value |
|---|---|---|---|---|---|---|
| Family size | 0.19 | 0.491 | ||||
| <5 | 54 (58.0) | 118 (63.5) | 0.79 (0.48 to 1.32) | 0.80 (0.44 to 1.4) | ||
| ≥5 | 39 (42.0) | 68 (36.5) | 1 | |||
| Educational status | <0.001 | <0.001 | ||||
| Illiterate | 44 (47.3) | 65 (35) | 1.8 (1.36 to 2.42) | 1.82 (1.30 to 2.5) | ||
| Literate | 49 (52.7) | 121 (65.0) | 1 | |||
| Monthly income | 0.18 | 0.380 | ||||
| <5000 ETB | 75 (80.6) | 135 (72.5) | 1.57 (0.85 to 2.88) | 1.37 (0.67 to 2.7) | ||
| >5000 ETB | 18 (19.4) | 51 (27.5) | 1 | |||
| Occupational status | 0.26 | 0.59 | ||||
| Housewives | 58 (62.4) | 122 (65.6) | 0.86 (0.51 to 1.45) | 1.0 (0.55 to 1.8) | ||
| Employed | 35 (37.6) | 64 (34,4) | 1 | |||
| Place of residence | <0.001 | <0.001 | ||||
| Rural | 78 (83.8) | 102 (54.8) | 4.2 (2.29 to 7.98) | 4.0 (2.0 to 8.1) | ||
| Urban | 15 (16.2) | 84 (45.2) | 1 | |||
| Birthplace of child | 0.0002 | 0.006 | ||||
| Home | 51 (54.8) | 78 (42.0) | 2.05 (1.24 to 3.41) | 2.30 (1.27 to 4.1) | ||
| Health institution | 42 (45.2) | 108 (58.0) | 1 | |||
| ANC follow-up | 0.001 | 0.003 | ||||
| Yes vs No | 31 (33.0) | 104 (56.0) | 0.45 (0.27 to 0.77) | 0.51 (0.28 to 0.9) | ||
| PNC follow-up | <0.001 | 0.001 | ||||
| Yes vs No | 38 (41.0) | 107 (58.0) | 0.51 (0.30 to 0.84) | 0.46 (0.25 to 0.8) | ||
| Maternal knowledge | <0.001 | <0.001 | ||||
| Satisfactory | 29 (31.0) | 104 (56.0) | 0.35 (0.21 to 0.6) | 0.30 (0.16 to 0.5) | ||
| Poor | 64 (69.0) | 82 (44.0) | 1 |
ANC, antenatal care; AOR, Adjusted OR; COR, Crude OR; ETB, Ethiopian birr; PNC, postnatal care.
Sensitivity analysis
The sensitivity analysis using Poisson regression yielded results consistent with the primary logistic regression findings. Higher numbers of missed vaccine doses were observed among children of mothers with no formal education, those residing in rural areas and those born at home. In contrast, antenatal and PNC attendance and satisfactory maternal knowledge of immunisation were associated with fewer missed doses. The direction and strength of these associations remained stable after adjustment for potential confounders, supporting the robustness of the main results (table 4).
Table 4. Bivariable and multivariable Poisson regression analysis of factors associated with the number of missed vaccine doses among children aged 12–23 months (sensitivity analysis).
| Variable | Category | Crude IRR (95% CI) | Adjusted IRR (95% CI) | P value |
|---|---|---|---|---|
| Family size | 0.491 | |||
| <5 | 0.88 (0.67 to 1.15) | 0.91 (0.65 to 1.28) | ||
| ≥5 | 1.00 | 1.00 | ||
| Educational status | <0.001 | |||
| Illiterate | 1.46 (1.20 to 1.78) | 1.48 (1.18 to 1.86) | ||
| Literate | 1.00 | 1.00 | ||
| Monthly income | 0.380 | |||
| <5000 ETB | 1.29 (0.91 to 1.82) | 1.21 (0.83 to 1.77) | ||
| ≥5000 ETB | 1.00 | 1.00 | ||
| Occupational status | 0.59 | |||
| Housewives | 0.93 (0.71 to 1.22) | 1.02 (0.73 to 1.43) | ||
| Employed | 1.00 | 1.00 | ||
| Place of residence | <0.001 | |||
| Rural | 1.72 (1.38 to 2.14) | 1.64 (1.27 to 2.12) | ||
| Urban | 1.00 | 1.00 | ||
| Birthplace of child | 0.006 | |||
| Home | 1.41 (1.14 to 1.75) | 1.36 (1.09 to 1.71) | ||
| Health institution | 1.00 | 1.00 | ||
| ANC follow-up | 0.003 | |||
| Yes vs No | 0.68 (0.54 to 0.86) | 0.72 (0.56 to 0.93) | ||
| PNC follow-up | 0.001 | |||
| Yes vs No | 0.70 (0.56 to 0.88) | 0.66 (0.52 to 0.84) | ||
| Maternal knowledge | <0.001 | |||
| Satisfactory | 0.61 (0.48 to 0.77) | 0.58 (0.44 to 0.76) | ||
| Poor | 1.00 | 1.00 |
Poisson regression was performed as a sensitivity analysis using the number of missed vaccine doses as a count outcome.
ANC, antenatal care; ETB, Ethiopian birr; IRR, incidence rate ratio; PNC, postnatal care.
Summary of key findings
A total of 279 mothers/caregivers participated in the study (response rate 100%). Most mothers were aged 26–34 years, and females predominated among children in both groups. Vaccination cards were available for 48% of cases, and 54.8% of cases were born at home.
Coverage of individual vaccines among cases ranged from 61.7% for measles to 83% for pentavalent 1, while controls had 100% coverage for all vaccines. Maternal knowledge of childhood immunisation was satisfactory in 31% of cases and 56% of controls. ANC follow-up was reported by 33% of cases and 56% of controls and PNC follow-up by 41% of cases and 58% of controls.
Bivariable and multivariable logistic regression identified maternal education, place of residence, birthplace of the child, ANC and PNC attendance and maternal knowledge as significantly associated with incomplete immunisation. Children of mothers with no formal education, those living in rural areas and those born at home had higher proportions of incomplete immunisation, while higher maternal knowledge and attendance of ANC and PNC were associated with lower proportions of incomplete vaccination.
Discussion
This study identified several factors associated with incomplete immunisation among children aged 12–23 months in Koore Zone, including maternal education, rural residence, home delivery, maternal health service utilisation and caregiver knowledge. These associations suggest that children from households with limited maternal education or restricted access to health services may face structural and informational barriers that reduce timely vaccination.
For example, mothers with limited education may have lower awareness of vaccination schedules or may be less confident in navigating health services, which aligns with evidence from other rural regions of Ethiopia. Our findings are consistent with studies from Arbegona, Jigjiga and other regions of Ethiopia, where maternal education and residence were significantly associated with immunisation completeness.25,27 Similarly, evidence from low- and middle-income countries, such as rural Bangladesh and Kenya, shows that maternal knowledge, access to ANC and PNC and facility-based delivery are strongly linked to higher vaccination uptake.28,30 By focusing on the Koore Zone, this study adds to the literature by providing context-specific insights in a predominantly rural and ethnically diverse setting, highlighting local challenges that may not be captured in national surveys or urban-focused studies.
Maternal education was associated with higher likelihood of complete immunisation in this study. These findings suggest that maternal education may play an important role in vaccination uptake. Interventions targeting maternal knowledge and awareness could potentially support improved immunisation coverage, though causal relationships cannot be established from this study. This finding aligns with studies conducted in Arbegona district and other regions of Ethiopia, where maternal literacy was positively associated with vaccination completion.25 26 Educated mothers have better health knowledge, decision-making skills and access to information, enabling them to adhere to vaccination schedules. In contrast, illiterate mothers may face challenges understanding or trusting vaccination-related messages, potentially delaying or missing doses.
Rural residence was associated with incomplete immunisation in our study population. This is consistent with studies in Ethiopia and other low- and middle-income countries, where rural residency is linked to lower vaccination coverage due to geographic, socioeconomic and infrastructural barriers.27 28 Limited access to health facilities, long travel distances, poor transportation infrastructure and reduced exposure to health education contribute to incomplete immunisation in rural communities. Conversely, some studies in rural Ethiopia did not find residence to be significant, likely reflecting successful local outreach programmes or differing health service infrastructure.29
Home delivery significantly increased the likelihood of incomplete immunisation, with children born at home more likely to miss vaccines compared with facility births. Similar findings were reported in Kaptembwo, Kenya, and Jigjiga, Ethiopia, highlighting the positive impact of facility-based births on early vaccination initiation and adherence to immunisation schedules.30 31 Facility delivery provides immediate counselling, early initiation of BCG and polio vaccines and linkage to routine follow-up schedules. Home deliveries, on the other hand, often result in missed opportunities and reduced engagement with healthcare providers.
ANC and PNC attendances were positively associated with immunisation completion, indicating their potential relevance in supporting child vaccination. These results corroborate findings from Kenya and the Somali region, Ethiopia, where maternal health service use facilitated timely vaccination.32 33 ANC and PNC visits provide structured opportunities for health education, counselling on the vaccination schedule and reinforcement of the benefits of completing vaccines. Mothers who attend these services are more likely to follow recommendations, whereas non-attendees may lack critical knowledge.
Satisfactory maternal knowledge was associated with better immunisation completion, consistent with studies from rural Bangladesh and Nigeria.34 35 Knowledgeable mothers understand the importance of timely and complete vaccination, whereas poor knowledge may lead to missed or delayed immunisations due to misconceptions or forgetfulness. Behavioural factors, such as fear of vaccine side effects, also contributed to incomplete immunisation, reflecting findings from Uganda, where parental concerns led to delayed or refused vaccines.36 37
Health system-related factors, particularly vaccine stock-outs, were reported by some mothers as reasons for missed doses. In the Sinana district, Ethiopia, over half of mothers returned without vaccinating due to the unavailability of vaccines.38 Stock-outs reduce caregiver motivation and may result in permanent default from immunisation schedules, emphasising the importance of strengthening supply chain management.
Implications and knowledge contribution
These findings extend the current understanding of incomplete immunisation in Ethiopia by identifying contextual and caregiver-level factors that could be targeted in future interventions. They emphasise the importance of improving caregiver awareness, supporting maternal health service utilisation and addressing rural access barriers. While the study does not establish causality, it provides evidence to guide locally relevant strategies and identifies priority areas for further investigation.
Strengths and limitations
This community-based unmatched case-control study allowed robust identification of predictors of incomplete immunisation. The structured, interviewer-administered questionnaire adapted from WHO and UNICEF tools ensured data reliability. Random selection of study subject and proportional allocation of cases and controls improved representativeness. Limitations include potential recall bias regarding immunisation history, social desirability bias in caregiver responses and the inability to infer causality due to the observational design. While our study measured overall vaccine coverage and completeness, it did not collect data on the timing or delays of individual vaccinations. Future studies should explore this aspect, as delayed doses may reduce protection and contribute to incomplete immunisation.
Conclusion
In the Koore Zone, incomplete immunisation among children aged 12–23 months was associated with maternal education, rural residence, home delivery, ANC and PNC attendance and maternal knowledge. These findings indicate the need for targeted interventions. Strengthening maternal education, community engagement and community outreach services, alongside improved ANC and PNC utilisation, may enhance immunisation coverage. Expanding rural outreach can help reduce geographic barriers, while effective health communication should address knowledge gaps and vaccine safety concerns. Ensuring consistent vaccine availability at health facilities remains essential. As this was a case-control study, causal relationships cannot be inferred, and further longitudinal research is warranted to inform policy and practice.
Supplementary material
Acknowledgements
The authors would like to express their sincere gratitude to the study participants, data collectors, supervisors, and the Koore Zone Health Department for their support throughout the study.
Footnotes
Funding: The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Provenance and peer review: Not commissioned; externally peer reviewed.
Patient consent for publication: Consent obtained from parent(s)/guardian(s).
Data availability free text: The datasets generated and analysed during the current study are available from the corresponding author on reasonable request.
Patient and public involvement: Patients and/or the public were not involved in the design, conduct, reporting or dissemination plans of this research.
Ethics approval: Ethical clearance was obtained from the Institutional Review Board of Hawassa University, College of Medicine and Health Sciences, School of Public Health (approval number: IRB/029/17). Written permission was obtained from the Koore Zone Health Department. Informed written consent was obtained from all study participants prior to data collection. Participants were informed that their participation was voluntary and that they could withdraw at any time without consequences.
Data availability statement
Data are available upon reasonable request.
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