We grouped the concepts identified in our analysis into five thematic categories in accordance with the SEM framework, including (a) intrapersonal (b) interpersonal (c) institutional (d) community and (e) policy (Fig. 1). Despite the differentiation of the five categories, many variables were intertwined, which is consistent with the concept of reciprocity described in the SEM.
The intrapersonal level of the SEM represents individuals’ characteristics, including knowledge, attitudes, and behaviors (11). These are consistent with concepts posited by individually-focused behavioral theories, such as the Health Belief Model, that are expected to affect childhood immunization uptake or practice (13, 14). Participants in our study shared several individual-level factors that influenced caregivers' uptake of childhood immunization services. These intrapersonal factors included those that are intrinsic, such as knowledge, and extrinsic, referring to factors such as the caregivers' time constraint. Participants reported caregivers' knowledge of immunization services as being influential to immunization uptake. Essential elements of knowledge included understanding vaccine benefits, such as preventing disease and being aware of the immunization schedule delineating the age at which specific vaccines were recommended. A related but separate theme was caregivers' negative beliefs and misperceptions of immunization.
One of the most frequently-discussed individual-level factors was caregivers' time constraints or conflicting work schedules. This theme was related to an organizational-level theme discussed below: clinic waiting times. Caregivers' welfare and love of children was another individual-level factor that participants described as being important to consider for its role in immunization uptake. This theme relates to the affection or well-being of their child that drives vaccine decisions.
The following excerpt captures one discussion about the importance of individual-level determinants of vaccine uptake.
"Everything is not about money, and everything is not….. it depends on the knowledge……..it is not everybody that has the knowledge of this immunization, what is it called? It's not compulsory; it is not everybody. To me, majority of people are ignorant, and some people that are not ignorant some people don't know what they are calling immunization, they don't know the value, they don't know what it is called, they don't know what it takes from the baby, the necessary thing, what that immunization is doing for the baby so I think that maybe they should try like when they are doing ante-natal, they should try to make it for them to understand it. Even though some parents will say, "Ha! No, I don't want". But we should not look at the argument when they are talking; we should not look at their manner, they should try to bring them to their standard."
Individual-level factors reported by participants were affected by determinants across all other SEM levels, especially those relating to members of caregivers' families or social networks.
The interpersonal level of the SEM describes individuals' familial and social networks, which may influence healthcare practices and contribute to various experiences (11). Strong interpersonal dynamics in these relationships are thought to significantly affect an individual's physical and mental health and health decision-making (15–20). Studies have shown that social influence from interpersonal relationships significantly affects health behaviors, including health-seeking behavior, breastfeeding practices, and uptake of family planning methods (21–26). This also applies to immunization, as literature has highlighted that people who believe that individuals within their social network want them to be vaccinated are more likely to accept vaccines (27–30). Studies have also shown that as acceptance of vaccination within a community increases, making it a social norm, vaccine uptake by people within that community will also increase (27, 31).
In our study, participants discussed interpersonal factors, including those relating to the caregivers' relationships and social networks, including family, friends, and neighbors. Some caregivers in our focus groups discussed how other mothers within their networks had educated them about immunization and encouraged them to immunize their wards. They emphasized the importance of peers sharing their knowledge of vaccination with their peers. Caregivers also highlighted the roles that husbands, mothers, and mothers-in-law played in their decision-making about childhood immunization. Intergenerational roles were seen as being particularly influential on immunization decision-making; however, the impact of these roles varied based on the level of knowledge of these influencers.
"I have a friend who says her mum is a medical doctor; her aunt is a medical doctor; she comes from a medical doctor family. And she always listens to what they tell her and collect medicines or anything health-related from their hands."
However, we also found that intergenerational influences could also serve as a barrier to vaccine uptake in situations where senior family members carried misinformation or negative attitudes about immunization.
The institutional level describes the roles that characteristics and operations of social institutions, including health facilities and their health workers, play in shaping health care decision-making (11). Studies have shown that availability and access to health care facilities significantly affect care-seeking behavior and utilization of health services (32–35). In addition, patient-health care worker communication significantly impacts healthcare utilization, decision-making, acceptance of recommended health behaviors, and medical management (36–38). Researchers have highlighted that immunization uptake increases when healthcare workers educate and recommend immunization to caregivers (33, 39).
Our study participants also discussed health facilities and healthcare workers' impact on childhood immunization decision-making and uptake in Lagos. Some important facility-related factors included access, either geographical, such as bad roads leading to the facility, or financial, including transportation cost. However, the attributes of health facilities were also discussed. Facilities with poor waiting areas or lack of adequate ventilation or cooling systems such as fans or air conditioners made some caregivers reluctant to access them. Resources offered by facilities were also influential, and participants highly regarded facilities that provided free consumables such as cotton wool, gloves, and drugs. The mothers also valued incentives offered by facilities, and the incentives described included mosquito nets or baby products for new mothers.
The role and attributes of health workers were also described in much detail. Understaffed facilities resulted in long wait times, so caregivers placed value on facilities with adequate staff coverage, including record-keeping personnel. However, there were also many discussions about attitudes and personal attributes of the healthcare workers as influencing the likelihood of accessing childhood immunization. Some participants had previously had experiences with healthcare workers they described as rude, which they reported would affect vaccine access in the future. Others discussed the importance of having healthcare workers who could educate them about the importance of immunizations for their children.
Participants described facility- and health worker-related factors that influence childhood immunization uptake as follows:
"For example, this place wasn't the way it looks now, but when the place was equipped, and there are doctors on the ground. Since all had been put in place, people have been trooping in. Especially if you come around on Mondays, you will see the turnout of people. This gives people the confidence that when they come, they will be attended to."
"We spend almost the whole day in the health center to immunize our children. If there are more nurses, we will be able to get immunization quickly and do other things that day."
Community-level determinants include basic resources and the social and physical environment that comprise the greater community (11). The nature of infectious diseases, including those that are vaccine-preventable, highlights the importance of the social context of risk perception on vaccine uptake since one's concerns about their children becoming infected or transmitting disease to others would likely impact vaccine decision-making. Additionally, herd immunity plays a vital role in the spread of infection, making immunization a community-based effort (3). These factors may influence the actions of community leaders and community-based health workers. Social dynamics within a community, therefore, play a role in the perception of risk. Numerous studies have highlighted multiple factors impacting vaccine uptake at the community level, including the incidence and prevalence of the disease in one's community. In some communities, especially those in developing countries, informal networks including community and traditional leaders have played a role in their community's immunization practices (30, 33, 40).
In our study, themes that emerged as community-level influences on immunization update encompassed factors within the environments where people live, including influences of informal networks such as community leaders and the availability of community resources. Participants discussed the impact of a community outreach, which they described as immunization services provided by healthcare workers within the community to increase immunization coverage, especially in underserved areas. Participants also described the value of house-to-house immunization campaigns conducted by trained volunteers, such as National Immunization Plus Days (NIPDs), during which supplemental oral polio vaccine is distributed on a house-to-house basis to children less than five years of age.
Furthermore, caregivers, community leaders, and healthcare workers in our study described the importance of leveraging community resources such as community leaders, including traditional and religious leaders, and those in formal community leadership positions such as members of the Ward Development Committee. One of the participants described the effect of community influences on childhood immunization uptake as follows:
"Like we have outreaches now that we do every Wednesday. I think the outreach is helping us a lot. The mothers that can't come to PHC, the outreach workers- the people that go for outreaches go to their communities to immunize them, and that is even increasing our immunization coverage."
The outermost tier of the SEM, policy, accounts for the local, state, and national laws and policies that impact health practices (11). Policies play a fundamental role in access to healthcare services, utilization of healthcare services, and the adoption of healthy behaviors (41). For example, there is ample evidence that universal healthcare coverage increases access to healthcare services, including immunization (41–43). Similarly, the presence of public or organizational policies providing women with paid maternity leave has been found to increase breastfeeding initiation and duration (44–46). Policies that ensure access to health insurance that covers immunization have also been found to determine access to immunization services, therefore, playing a significant role in immunization decision-making (42, 47, 48).
In Nigeria, various laws and policies govern immunization services, which differ between federal, state, and local governments. Lagos state has an immunization supply chain policy, ensuring the availability of adequate vaccines and devices at health facilities. Participants in our study described the critical importance of free immunization services, a national health policy meant to provide these free services in all health facilities. However, participants discussed how these differed by type of health facility in that whether or not a facility was public or private impacted the availability of free immunization services. Additionally, consumables, such as gloves for healthcare workers, were not always available free of charge in public healthcare facilities. Another policy described by participants as crucial to vaccine uptake was the provision of child immunization cards, a national policy whereby all children are provided with an immunization card to record vaccines taken, and subsequent appointment dates. Participants in our study indicated the child immunization cards helped caregivers to track immunization schedules and helped caregivers to access vaccines in different healthcare facilities if they were traveling.