*Caregiver Exit Interviews*

At 12 months after container clinic implementation (September 2018), we conducted caregiver exit interviews. These were conducted to understand the characteristics of the populations being served and the acceptability of the clinics among the caregivers, and to compare those experiences to the health services they received prior to the clinics' implementation. We set the convenience sample to a target size of 60 exit interviews per clinic—calculated based on monthly attendance data—or until four weeks of data collection had passed (whichever occurred first). The criteria for participation in the exit interviews included being at least 16 years of age and a caregiver of a child under five. Attending the clinic for immunization was not a criterion for participation.

Information collected from the caregiver exit interviews included demographic variables such as the caregiver's age (years), child's age (months), whether or not they were a resident of the community (yes/no), profession (head porter/merchant/hairdresser/seamstress/unemployed/cleaner/other), and educational attainment (none/primary/junior high secondary/senior high secondary/university/unknown). Then, the interviewers proceeded to ask the caregivers about their experiences in accessing services at the container clinics using a structured questionnaire. The questions were aligned with the four dimensions of access including the availability of child health services provided by the container clinics (e.g., the ease of receiving child health care), geographic accessibility (e.g., the convenience of the location, location traveled from, and time spent traveling to the clinic), financial accessibility (e.g., missing work to come to the clinic for child health services), and acceptability (e.g., satisfaction and intention to return). We conducted interviews using tablets with forms programmed in Open Data Kit [14] and uploaded them to SurveyCTO [15].

#### *Qualitative Focus Group Discussions and In-Depth Interviews*

In September 2018, we also conducted caregiver and nurse focus group discussions (FGDs) and community leader and health authority in-depth interviews (IDIs) at both sites. Caregivers were selected using convenience sampling. The eligibility criteria included living in the catchment area of the container clinic and being a caregiver for a child under five, regardless of if they had attended the clinic. Groups were further stratified based on the caregiver having a child who was 0–23 months old or 24–59 months old. Nurses were eligible if they worked at the clinics before container clinic implementation. Community leaders were invited to participate if they held an authority role in their community and played a key role in setting up the clinic or its operations. Health authorities were selected if they were in a management role or had a unique historical background on the clinic. Guides for FGD and IDIs focused on themes related to access and the group or individual's perceived change in community access to childhood immunization services.
