Table 2. Characteristics of the social capital interventions and their impacts on human papillomavirus immunization.

Study (in alphabetical order)	Objective	Country, population size and description	Description of intervention	Social capital dimensions	Social capital functions	Impact and effectiveness
Chu et al., 2021	This one-group quasi-experimental study evaluated the impact of a culturally developed educational intervention for East African immigrant mothers to improve HPV vaccination knowledge, attitudes and intentions to vaccinate their male and female children.	United States 120 participants Sex: female, 100% Age: <30 years, 2.6%; 30–39 years, 57.0%; 40–49 years, 33.3%; ≥50 years, 7.0%	A socio-context framework and Andersen’s behavioural model were applied to include social, cultural and religious factors to inform a community-based education intervention delivered by co-ethnic health professionals. A communal dinner for all participating mothers and their children was held prior to the implementation of the education forum. The forum included a 40-minute interactive session with the co-ethnic health professional, a 20-minute presentation in the participants’ native languages and a 20-minute question and answer period.	Cognitive: · Social norms and influences were measured using survey items. · Focus group findings deepened the understanding of social influences (social, cultural, religious factors). These findings on contextual factors informed the development of the intervention.	Bridging and bonding: · The intervention was designed to be sensitive, language and culturally appropriate and audience-centric to appeal to the East African community.	· Within 6 months of the intervention, only 2% (n=2) of the 96 mothers with children who had no HPV vaccination records received the HPV vaccine. · The proportion of mothers who wanted to vaccinate their children increased after intervention (6.3%; n=7/111 to 75.7%; n=84/111). · Post-intervention, 86.4% (n=95/110) of mothers reported that they were more likely to talk with their children’s doctors about the HPV vaccine than pre-intervention (p<0.0001). · Post-intervention, mothers had a significant increase in knowledge and beliefs about HPV (p<0.0001; RR 3.64; 95% CI: 2.89–4.60), HPV vaccination (p<0.0001; RR 8.10; 95% CI: 5.26–12.45) and reported positive HPV vaccination intentions (p<0.0001; RR 5.03; 95% CI: 3.42–7.39). · Post-intervention, 90.2% (n=101/112) of mothers thought they had enough information to make a decision about vaccinating their children and 92.4% (n=97/105) knew where to get the HPV vaccination compared to baseline (11.6%; n=13 and 25.7%; n=27 respectively; p<0.0001).
Lee et al., 2018	This randomized controlled trial examined the feasibility, acceptability and effectiveness of a narrative intervention to promote HPV immunization in Cambodian mothers and daughters.	United States 18 dyads (38 total mothers and daughters), 9 in the intervention and 9 in the control group. Mean age: daughters, 15.3 years old; mothers, 44.9 years old	The intervention included a storytelling narrative of HPV immunization, which was informed by the network episode model. This model describes that interpersonal interactions (e.g., peer influence) within social networks function as a mechanism for health-related decision-making; thus, it is both a social and individual process. The storytelling narrative was a 26-minute storytelling DVD that utilized unscripted, culturally grounded stories in the first person. The real stories increased realism by recruiting important people from the Khmer community, such as physicians and community members who were both vaccinated and unvaccinated. The control group received non-narrative education materials.	Structural: · Narrative intervention employed community members, friends, family and doctors (social networks) to encourage vaccination behaviours. Cognitive: · The storytelling narrative was developed by other Khmer mothers, daughters and community health leaders. · Participants were recruited through community health leaders, site coordinators and cultural navigators’ social networks in addition to other methods, such as advertising on local radios.	Linking: · Trusted community health leaders utilized their social networks to aid in study recruitment. Bridging: · Participants, community health leaders and actors within the storytelling narrative were all part of the Khmer community. While these groups share similar characteristics or identities, they are part of different networks. Bonding: · Dyads of mothers and daughters were recruited because mothers are the primary health decision-makers for their daughters.	· Within one month, daughters from the intervention group reported higher intentions to receive HPV immunization than their control group counterparts. However, there was no difference in actual vaccination initiation between both groups. · Storytellers shared how they were personally influenced by their social networks and norms from friends, mothers and healthcare providers to receive the HPV vaccination. · Social network norms were effective in motivating the vaccination intentions of participants through a positive emotional reaction. Note: No statistical data was provided.

Abbreviations: CI, confidence interval; HPV, human papillomavirus; RR, relative risk