Experimental design and set-up
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We randomly selected barangays (‘small communities’) from Dasmariñas City (urban arm) and Silang, Cavite (rural arm) that had not previously participated in a qualitative component of the study (results of which are described elsewhereWe performed a multistage stratified sampling frame to select barangays. From each of the two study sites, two barangays with the highest population, based on the most recent population report available, were selected to ensure enough potential participants. The two selected barangays (per urban and rural arms) were randomly allocated as an intervention and as a control site. A listing of households with under-five children was obtained from the local health officials. The household listing served as a sampling frame from which 200 households were randomly selected and invited to participate in the study. In four originally sampled barangays (two each for control and intervention groups), the number of interviewed caregivers was less than 200. In line with the processes defined in the research protocol, we therefore sampled additional barangays as per the criteria above.We collaborated with community health workers who conducted house visits, obtained caregivers’ mobile phone numbers and obtained consent to be contacted by the research team, following the selection and allocation of the potential participants to intervention or control groups. Community health workers also distributed consent forms and informed potential participants that a member of the research team would contact them. Afterwards, the potential participants were invited to participate during a phone call where the study aims were briefly introduced. If individuals expressed interest in the initial phone contact, we either directly continued with a detailed study discussion and obtained online informed consent (via Facebook Messenger video call) or scheduled a separate appointment. To ensure participants’ internet connectivity throughout the consent process and trial procedures, we purchased and transmitted mobile data packages to participants.Once consent was obtained, the videos (intervention and control) and surveys (pre and post) were delivered online. We developed and used an online version of the survey forms, which we pilot-tested among 30 caregivers to ensure feasibility (either self-administered or data collector-assisted) and alleviate operational challenges. Following the pilot testing of the survey forms, we therefore decided to conduct data collector-assisted surveys (ie, data collectors read the questions to the participants and are responsible for encoding the answers in the online form). After completion of the baseline survey, the Salubong video was then screened for members belonging to the intervention group, while the ‘Before and after watching the intervention or control video, participants in both groups were asked to provide information about their attitudes toward vaccinations, with statements such as, ‘Children get more shots than are good for them’, ‘I believe that many of the illnesses that vaccinations prevent are severe’ and ‘It is better for my child to develop immunity by getting sick than to get a shot’, among others. We used the parents’ attitudes about childhood vaccination (PACV-15) adapted from Opel and colleagues.
