Introduction

Immunization is recognized as an essential and effective mechanism for controlling communicable diseases. However, childhood vaccination rates have been declining. The World Health Organization (WHO) estimates that 25 million children missed out on one or more vaccination doses in 2021, representing a five-percentage drop in coverage compared to the 2019 achievement [1].

Kenya has made remarkable progress in the rollout of childhood vaccination since the inception of the essential program for immunization in 1980 [2]. Immunization coverage, however, remains sub-optimal. Based on findings from the 2022 Kenya Demographic Health Survey (KDHS), only 55% of children aged 12 to 23 months had received all the vaccinations recommended for their age [3]. Vaccinations given within the first six weeks after birth have notably higher coverage. For instance, there was an eight-percentage difference in the completion rates of the diphtheria-pertussis- tetanus (DPT) vaccine between the first (97%) and the third dose (89%) [3].

Sub-national data analysis from the demographic survey also revealed variations in vaccination coverage across regions and marginalized groups. As per the national immunization schedule, the percentage of fully vaccinated children in Nairobi stood at only 45%, falling below the national average of 55%. Furthermore, full vaccination coverage was higher in the highest wealth quintile (59%) as compared to the lowest quintile (42%), while 3.5% of children in the lowest quintile had received no vaccinations, in comparison to 1.4% in the highest quintile [3].

Marginalized populations, such as those in urban slums, remote rural areas, or war-prone areas, are at higher risk of being unvaccinated [4, 5]. Additionally, one in five unvaccinated children under one year of age is estimated to reside in urban poor settlements [6]. A longitudinal study in two urban informal settlements in Nairobi reported on-time vaccination coverage below 50% [4]. The Immunization Agenda 2030 recognizes the urgency of reaching the most marginalized populations and integrating successful strategies for immunization delivery [7]. Given the higher risk of disease transmission and vaccine-preventable diseases (VPD) outbreaks across densely populated urban slums, identifying effective interventions to improve childhood vaccination in this vulnerable population is crucial [8].

A range of interventions, including reminders, health education, and motivational interviewing, have been found to be effective in promoting childhood vaccination uptake [9–11]. For instance, pre-and post-natal vaccination education can positively influence parental attitudes and beliefs about infant vaccination [11]. Intervention efforts for marginalized populations have majorly addressed supply-side barriers by improving accessibility and commodity management [12]. Some of the tested interventions in Kenya, including intensified fixed-point immunization services, door-to-door defaulter tracing by community health volunteers, and household-level immunization, have significantly boosted immunization coverage [12]. A combination of mobile phone text message reminders and incentives was also found to significantly improve immunization coverage and timeliness in a cluster-randomized controlled trial in Western Kenya [13]. A multidimensional perspective considering demand and supply-side barriers is pivotal in reversing the declining childhood vaccination uptake [8]. Exploring the social and behavioral dynamics that influence the demand for childhood vaccination facilitates the development of tailored interventions that consider cultural norms and community dynamics. Such interventions are more likely to be accepted and embraced by communities [14].

The WHO Behavioral and Social Drivers (BeSD) of vaccination conceptual model identifies four key domains influencing vaccination uptake. These include caregiver thoughts and feelings on vaccination (including risk perceptions and vaccine confidence), social processes like social norms and recommendations, vaccination intentions, and practical factors around seeking vaccination [15]. Public health programs must consider behavioral and social biases and address context-specific concerns to improve vaccination rates and reduce the burden of preventable diseases.

Applying behavioral sciences in exploring vaccination decision-making processes can help identify health system gaps contributing to under or untimely vaccination. Moreover, individual decisions on vaccination are influenced by how the vaccination choices are presented and how the actual decisions are made [16, 17]. Recognizing the role of beliefs and biases in vaccination decisions complements traditional supply-side approaches toward improving vaccination uptake [16]. In addition, understanding community-derived and context-specific behavioral preferences is vital in overcoming vaccine demand challenges and providing more client-centered care [18].

This study employed the Theory of Planned Behavior (TPB) as an initial conceptual framework to explore the socio-behavioral determinants of childhood vaccination in urban poor populations. TPB, a cognitive framework, encompasses three fundamental constructs: attitude (the individual’s positive or negative evaluation or appraisal of the behavior), subjective norms (perceived social pressure that encourages or discourages the behavior), and behavioral control (perception of how easy or challenging it is to perform the behavior) [19]. The constructs are posited to influence an individual’s intention to engage in a specific behavior, consequently affecting their actual behavioral performance. Previous research has demonstrated the significant predictive power of TPB constructs in relation to vaccination intentions [20, 21]. Kim and Choi (2016) found a 69.5% explanatory power for subjective norms, attitudes, and perceived behavioral control in predicting vaccination intentions [21]. By exploring how attitudes, subjective norms, and perceived behavioral control intersect to shape childhood vaccination, we aimed to identify opportunities tailored to address the unique needs and challenges in urban informal settlement populations. We also sought to expand on TPB constructs to identify emerging factors influencing vaccination uptake in urban poor settlements. This comprehensive approach facilitated an intricate understanding of the complexities surrounding sub-optimal vaccination within urban poor settlements. Consequently, this study explored the socio-behavioral factors contributing to sub-optimal childhood vaccination in the urban poor settlements of Nairobi, Kenya.

Methodology

Findings

A total of 39 caregivers, including both mothers and fathers of children under five years old, participated in the FGDs. The median age for the participants was 29 years (range 20–52). Most of the participants had completed secondary education (54%), while a fifth were male. See Table 1 for socio-demographic characteristics.

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Table 1. Socio-demographic characteristics of participants.

https://doi.org/10.1371/journal.pone.0303215.t001

The results are presented by themes, subthemes, and selected representative quotes and are summarized in four major themes (Table 2). The sub-categories,codes and qoutes are provided in S1 Table.

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Table 2. Summary of emerging themes.

https://doi.org/10.1371/journal.pone.0303215.t002

Discussion

This study explored the socio-behavioral factors influencing childhood vaccination behavior in urban poor settlements. Utilizing the grounded theory process facilitated concentration on the contextual and process-oriented aspects, along with the choices and behaviors of caregivers about whether they vaccinated their children. Starting with the theory of planned behavior (TPB), we explored the contextual behavioral and social factors that influence timely vaccination uptake in the informal urban settlements of Nairobi. The study findings indicate that perceived vaccine benefits, perceived disease risk, knowledge of vaccine effectiveness, perceived vaccine safety, trust in vaccines, and the vaccination process influence the caregiver’s attitude towards vaccination and their intent to vaccinate their children. Furthermore, cultural, and religious beliefs, social norms, peer influence, and community dynamics also shaped vaccination decisions and actions.

Various extensions of the TPB have been proposed to enhance its explanatory power and to provide a more robust theoretical framework for understanding the complex factors that influence human behavior. For example, the Integrated Behavioral Model (IBM) combines concepts from TPB with other factors, such as environmental constraints and salience of the behavior [28]. The Reasoned Action Approach (RAA), on the other hand, splits the three TPB constructs into pairs of separate yet interconnected sub-components. These include experiential and instrumental attitudes and injunctive and descriptive norms, while perceived control is divided into capacity and autonomy components [29]. Our findings align with the inclusion of instrumental attitude as a subset of TPB’s attitudes and beliefs [19, 29]. Instrumental attitude, in this sense, refers to beliefs about the expected outcomes from a particular behavior [31]. These are distinguished from affective attitudes, which refer to beliefs regarding the likely emotional consequences of behavior [30, 31]. To the latter, our findings suggest that positive and negative affective attitudes and anticipated regret—the adverse emotional reaction resulting from comparing the expected outcome of inaction to the outcome of taking action [32, 33]- may influence vaccination intentions.

Consistent with previous research [34], our findings also point to influences from healthcare providers, family, and friends on the caregivers’ decision to vaccinate their children. This direct influence by others, coupled with the need to conform to social systems and the fear of social judgment and self-stigma, can be aggregated under TPB’s subjective norms–beliefs about the perceived position of important others towards the behavior [19]. However, consistent with the thinking in social psychology, we find it important to distinguish between descriptive norms–the perceived prevalence or typicality of a given behavior, and injunctive norms as the perceived degree of social approval or disapproval of the behavior [35, 36]. Such distinction is essential because, as elaborated by Jacobson and colleagues [36], the descriptive norms provide information relevant to the intra-personal choice of appropriate behavior. At the same time, the injunctive norms include valuable information for guiding, building, and maintaining interpersonal and social relationships. These are, therefore, distinct forms of social influence that can be independently or concurrently targeted by a health promoter keen on understanding, predicting, and influencing health-seeking behavior. Health messaging needs to take cognizance of such social influences and be tailored to the cultural dynamics in the informal settlements.

Gender-related barriers were an important social factor influencing timely childhood vaccination uptake in informal settlements. Though the mothers were identified as the primary decision-makers in vaccinating their children, their male partners played a crucial role in supporting the vaccination process. The lack of financial autonomy among the mothers also greatly influenced their ability to have their children vaccinated on time. Empirical evidence exists. A study analyzing women empowerment and immunization data from demographic and health survey data from fifty countries found that children from mothers with low and medium levels of social independence had three times higher odds of not receiving diphtheria, pertussis, and tetanus (DPT) vaccines as compared to those with high levels of autonomy [37]. Children whose fathers were involved in vaccination decisions and processes were also perceived to be more likely to receive vaccination on time. Indeed, the Immunization Agenda 2030 recognizes the need for tailored strategies to overcome gender-based immunization barriers by increasing male involvement in vaccination through targeted communication to expand their inclusion in vaccination decisions and processes [38]. Involving fathers in decision-making and addressing their concerns about vaccines can help ensure that more children are vaccinated and protected.

The role of information in influencing attitudes, beliefs, and behaviors cannot also be gainsaid. In this study, we found that caregivers still have misconceptions and fears concerning the effects of vaccination that need to be addressed. Most of the misconceptions arise due to inadequate information on vaccination side effects. Other studies have also emphasized the negative impact of insufficient information among caregivers on their vaccination practices [39, 40]. When caregivers lack sufficient understanding, they may be more hesitant or resistant to vaccinating their children, leading to lower vaccination rates. Tailoring messaging to address specific caregivers’ concerns can help to alleviate fears or misconceptions that they may have about vaccines.

The study findings highlight the important role of healthcare providers’ interactions with caregivers in facilitating timely vaccination. Caregiver perceptions of negative treatment by healthcare providers were linked to their vaccination behavior. Similarly, in a study by Braka et al. (2012), participants stated that difficulties in approaching health providers increased their reluctance to communicate their vaccination concerns [39], underscoring the importance of good communication by providers in improving uptake.

Caregivers’ fear of being judged or stigmatized by providers or peers for various reasons also contributed to missed vaccination. This aligns with a study in Uganda that found that the stigmatization of mothers with poorly dressed children by health workers and other women was a barrier [41]. Interventions are needed, particularly in poor urban areas, to minimize missed vaccinations due to caregivers’ fear of being judged or stigmatized by healthcare providers or peers. Such interventions should promote non-judgmental attitudes towards caregivers, including training providers to provide respectful and supportive care to all caregivers regardless of their social status or other factors.

Finally, the respondents raised many practical issues, including accessibility, affordability, and ease of access to health services. Immunization programs need to identify interventions to minimize these missed opportunities, for instance, by using electronic immunization registers (EIRs) as sources of information on children’s vaccination status [42].

That said, our study has some limitations. We used CHVs to gain entry into the informal settlement communities. One potential limitation was the possibility of CHVs omitting eligible participants and favoring individuals they knew. To address this concern, the criteria for participant selection were clearly explained to the CHVs, but it is still possible that some degree of bias may have been present in the sample selection process. Another limitation is the potential difficulty in generalizing the findings due to the focus on urban poor settlements and the small number of participants, typical in qualitative studies. While our findings are based on research conducted in a specific urban poor settlement, they may still have potential applicability in other settings, including other urban informal settlements. Efforts to promote vaccination uptake should consider the unique characteristics in each setting while recognizing the common underlying factors that influence vaccination decisions. Third, during the data collection process, participants were sometimes prompted to discuss the experiences of their peers, which may have made it difficult to determine whether they were speaking about their own experiences or those of others. To address this, quotes were taken within the context of focus group discussions, which served as the unit of analysis.

Nonetheless, this study provides insights into the socio-behavioral factors influencing childhood vaccination in urban poor settlements. The findings allow us to improve and extend the theory regarding socio-behavioral influences. Consistent with the original TPB, intention is the most proximal predictor of behavior, while attitude, subjective norms, and control beliefs are the precursors to intention. However, we propose a clear distinction between instrumental and affective attitudes, and on subjective norms, we distinguish between injunctive and descriptive norms. By addressing these dimensions, interventions can resonate with caregivers’ vaccination outcome considerations, emotions, and connections, fostering greater acceptance and support [30].

Conclusions

In conclusion, the findings underscore the complex interplay of socio-behavioral factors in caregivers’ vaccination decisions for their children. The findings also support the extension of the TPB to include instrumental and affective attitudes as well as the distinction between injunctive and descriptive norms. These theoretical expansions facilitate a more precise understanding of vaccination decision-making and behavior, informing the development of improved strategies to promote vaccination uptake. The results also emphasize the importance of addressing barriers such as affordability, gender-related factors, information gaps, and healthcare provider attitudes to enhance vaccination uptake effectively.

Supporting information

Acknowledgments

The authors sincerely thank Sharon Limo, Judith Chepkemoi, Grace Mwai, and Bryan Onginjo for their invaluable assistance in the data collection phase. We would also like to thank the Nairobi County and Sub-County health management teams for their support in facilitating access to community health volunteers (CHVs). Finally, we extend our heartfelt appreciation to all the CHVs and caregivers who participated in the study.