Immunization is globally recognized as one of the most effective public health interventions for preventing infectious diseases in children, significantly contributing to reduced childhood morbidity and mortality rates (1). The Expanded Programme on Immunization (EPI), launched by the World Health Organization (WHO), has played a critical role in increasing global immunization coverage. In India, the Universal Immunization Programme (UIP) was introduced in 1985 to provide free vaccines against preventable diseases such as tuberculosis, poliomyelitis, diphtheria, pertussis, tetanus, hepatitis B, and measles (2).

Despite the advancements in healthcare infrastructure, urban slum populations continue to experience lower immunization coverage due to multiple socio-economic and systemic challenges. These include poor health awareness, low literacy levels, inadequate health-seeking behavior, limited access to healthcare facilities, and migration-related disruptions (3,4). Studies indicate that children living in urban slums are more likely to be under-immunized or not immunized at all compared to those in rural or non-slum urban areas (5).

Immunization coverage is often influenced by several maternal and child-related factors, including maternal education, socio-economic status, place of delivery, antenatal care (ANC) visits, and possession of immunization cards (6,7). Ensuring universal coverage in such high-risk populations is essential to achieving herd immunity and preventing outbreaks of vaccine-preventable diseases (8).

Given this context, it becomes essential to understand the current status of immunization coverage among under-five children in urban slums and the determinants influencing it. This study aims to assess the extent of immunization coverage and identify associated socio-demographic and healthcare-related factors in selected urban slums.

A sample size of 450 was calculated using the formula for prevalence studies, considering an expected full immunization coverage of 65%, 95% confidence level, and 5% allowable error, with an additional 10% to account for non-response. Stratified random sampling was employed. Slum clusters were considered as strata, and children were selected proportionately from each stratum using simple random sampling.

Inclusion and Exclusion Criteria:

Children aged 12–59 months residing in the selected slums for at least six months were included. Children whose parents or guardians were unavailable or who declined consent were excluded from the study.

Data Collection Tools and Procedure:

A pre-tested, semi-structured questionnaire was used to collect data through face-to-face interviews with the child’s primary caregiver, typically the mother. The tool captured socio-demographic details, immunization status, and healthcare-related factors. Immunization status was confirmed through immunization cards wherever available. In the absence of a card, caregiver recall was used.

Operational Definitions:

• Fully immunized: A child who had received BCG, three doses of DPT/OPV, and one dose of measles vaccine by 12 months of age.
• Partially immunized: A child who missed at least one of the scheduled vaccines.
• Unimmunized: A child who had not received any vaccine.

Statistical Analysis:

Data were entered into Microsoft Excel and analyzed using SPSS version 26.0. Descriptive statistics such as frequencies and percentages were used for baseline characteristics. Associations between immunization status and independent variables were assessed using chi-square tests. Variables found significant in bivariate analysis (p < 0.05) were included in multivariate logistic regression to identify independent predictors of full immunization. Adjusted odds ratios (AOR) with 95% confidence intervals (CI) were calculated, and statistical significance was set at p < 0.05.

A total of 450 children aged 12–59 months were included in the study. The mean age of the children was 36.2 ± 13.8 months, and 51.1% were male. The majority of respondents (74.4%) were mothers, and 62.9% of the families belonged to the lower socioeconomic class.

Immunization Status

Among the total children surveyed, 298 (66.2%) were found to be fully immunized, 110 (24.4%) were partially immunized, and 42 (9.3%) were not immunized. The coverage rates for individual vaccines are shown in Table 1.

Table 1: Vaccine-Wise Immunization Coverage (n = 450)

Table 1 shows that BCG had the highest coverage, whereas Vitamin A had the lowest among the listed vaccines.

Socio-Demographic Factors

The distribution of immunization status by socio-demographic characteristics is presented in Table 2. A significantly higher proportion of children with educated mothers (≥ primary school) were fully immunized compared to children of uneducated mothers (76.5% vs. 49.3%, p < 0.001). Institutional delivery and possession of an immunization card were also associated with higher coverage.

Table 2: Association of Socio-Demographic Variables with Full Immunization (n = 450)

As shown in Table 2, maternal education, place of delivery, ANC visits, and immunization card availability were significantly associated with full immunization status.

Multivariate Logistic Regression

On multivariate analysis, the factors that remained independently associated with full immunization were maternal education (AOR: 2.7; 95% CI: 1.6–4.5), institutional delivery (AOR: 3.2; 95% CI: 1.9–5.3), possession of immunization card (AOR: 4.1; 95% CI: 2.3–7.0), and ≥ 3 ANC visits (AOR: 2.9; 95% CI: 1.7–4.9) (Table 3).

Table 3: Predictors of Full Immunization – Multivariate Logistic Regression

Table 3 highlights the independent predictors of full immunization after adjusting for other variables.

These findings underscore the importance of maternal education, institutional delivery, and adequate antenatal care in ensuring complete immunization among under-five children in urban slums.

This study revealed that 66.2% of under-five children residing in urban slum areas were fully immunized, which, while moderate, falls short of the national goal of universal immunization coverage under India’s Universal Immunization Programme (UIP). The findings are consistent with other studies conducted in urban low-income settings across India and South Asia (1,2). Despite increased governmental focus on immunization drives, gaps persist due to several interrelated socio-economic and health system barriers.

Maternal education emerged as a strong determinant of full immunization, aligning with earlier studies which showed that educated mothers are more likely to understand the importance of vaccines and comply with immunization schedules (3,4). Education enhances awareness about disease prevention and improves health-seeking behavior, especially in underserved communities (5).

Institutional delivery was another significant predictor, possibly because it facilitates early maternal contact with healthcare services, ensuring timely dissemination of immunization-related information and postnatal services (6). This finding concurs with results from studies conducted in Delhi and Uttar Pradesh, where institutional delivery was positively correlated with better immunization coverage (7,8).

Possession of immunization cards was strongly associated with complete vaccination. This is in line with previous literature suggesting that immunization cards not only aid in maintaining accurate vaccination records but also serve as a reminder system for caregivers (9). However, card loss and poor maintenance remain challenges, particularly in transient slum populations (10).

Antenatal care (ANC) visits were significantly associated with better immunization outcomes. Mothers attending at least three ANC sessions were more likely to be informed about childhood vaccination schedules and benefits. Similar associations were reported in community-based studies in Rajasthan and Bangladesh (11,12). ANC serves as a platform for counseling and health education, which can influence postnatal care practices including immunization.

The present study also found that children from households with lower socio-economic status had significantly lower immunization rates. Economic constraints may hinder access to health services and indirectly impact the prioritization of preventive healthcare (13). Moreover, lack of health infrastructure, irregular supply of vaccines, and overburdened health workers in urban slums further complicate the issue (14).

Despite these barriers, immunization coverage for BCG and OPV was relatively higher, possibly due to their administration at birth or during early postnatal visits. However, coverage for measles and Vitamin A was considerably lower, likely because these vaccines are administered at a later age, which may be missed due to migration, loss to follow-up, or misconceptions regarding vaccine safety (15).

Strengthening maternal education through community outreach, improving antenatal and institutional delivery services, and ensuring reliable access to immunization cards may significantly improve coverage. Health system interventions such as mobile health teams, slum-targeted outreach sessions, and integration of immunization reminders through digital platforms could further enhance outcomes.

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