Table 4.

Program activities and mechanisms

Study	Program name	Activities	Mode of contact	Program theory or hypothesis
Adams, Judith. 2020 (27).	Peer Navigation	Clinical liaison and communication; practical support and material aid.	One home visit for missed appointment.	No underlying theoretical framework or explanation of peer influence reported.
Cabral H, 2018 (28).	Peer Navigation	Linkage and referral; practical support and material aid; information and education; emotional and social support.	7 (60 min every 1–3 weeks) sessions and weekly check-ins by phone or in person which ranged from 30 to 60 min or every 2 weeks for up to 4 months.	Based on social support framework, peers enhance the effect of program activities through greater credibility, trust, empathy and understanding.
Cataldo F, 2017 (29). Hosseinipour M, 2017 (36). Phiri S, 2017 (45).	Mentor or expert mother	Information and education; emotional and social support.	Support available in clinic or during home visits during 2-year trial period. Appointment reminders via phone or home visits.	Peers have more time to support patients with issues of disclosure, stigma and treatment initiation. No underlying theoretical framework or explanation of peer influence reported.
Chang LW, 2015 (30). Monroe A, 2017 (41).	Peer Support	Clinical liaison and communication; linkage and referral; information and education; emotional and social support.	Monthly visits for 12 months. Visits typically occurred in the home but could be arranged at other locations or in clinic.	IMB model used to explain how peers were able to enhance the effect of program activities, motivation and the uptake of information and behavioural skills through greater empathy and understanding.
Chevrier C, 2016 (31).	Ashraya (local language term) volunteers	Coaching and skills building; practical support and material aid; emotional and social support; advocacy.	Accompaniment to healthcare appointments and intervention in instances of discrimination in community. Care facilities were also available at CHO. Duration not reported.	Based on social empowerment theory, social support and advocacy acted as a buffer to negative effects of stigma and discrimination. Qualitative findings established that peers had a higher degree of credibility and that empathy and understanding enhanced the effect of activities.
Cunningham W, 2018 (32).	Peer Navigation	Clinical liaison and communication; practical support and material aid; information and education; coaching and skills building.	1–2-hour sessions were conducted, once during pre-release and in community settings post-release for a 24-week period, including accompaniment to 2 medical care appointments.	Based on social learning theory, peers were trusted sources of information and effective role models for behavioural skills and strategies to overcome stressors and barriers to desired health outcomes.
Giordano TP, 2016 (33). Minick SG, 2018 (42).	Peer Mentoring	Linkage and referral; information and education; coaching and skills building; emotional and social support.	2 in person 20–45-minute sessions in hospital, followed by 5 telephone calls after discharge over the next 10 weeks.	IMB model used to explain how peer mentors enhanced motivation and program activities through role modelling, credibility, trust, empathy and understanding.
Graham SM, 2015 (34).	Peer Navigation and Kiswahili language term Washikaji (meaning ‘‘those who bond or stick together’’).	Information and education; emotional and social support.	In person or by telephone at least weekly during the first month of ART, then at least monthly for the remaining follow-up.	Novel framework proposed that access, information, motivation, and proximal cues to action are necessary to engage participants in care and treatment. Peers enhanced all aspects of the model through role modelling and establishing trust and credibility.
Griffith D, 2019 (35).	Peer Navigation	Clinical liaison and communication;	Phone and text conversations. Duration not reported.	An interdisciplinary care team with specific training in youth-focused care, including peer navigator would better meet needs of youth PLHIV. No underlying theoretical framework or explanation of peer influence reported.
Karwa R, 2017 (37).	Peer Navigation	Linkage and referral; information and education; practical support and material aid.	Navigators met with patients on wards. In-patient and out-patient follow up was then provided. Duration not reported.	Peers enhance program activities through role modeling and greater empathy and understanding. No underlying theoretical framework reported.
Koneru A, 2017 (38).	Peer Navigation	Clinical liaison and communication; linkage and referral; information and education; practical support and material aid; emotional and social support.	Clinic-based appointments, accompaniment and phone call or text reminders. Duration not reported.	Peer navigators were likely to have greater credibility and acceptability among women living with HIV due to sharing similar experiences and backgrounds. No underlying theoretical framework reported.
Lifson AR, 2017 (39).	Peer Community Health Support Worker	Clinical liaison and communication; linkage and referral; information and education; coaching and skills building; emotional and social support.	1–4 visits monthly for a year. Additional phone calls for clinical contact and referrals.	Based on social support and social learning theory, role modelling and greater understanding and empathy from peers enhanced program activities.
Maulsby C, 2015 (40).	Peer Health Navigation or Community Health Outreach Worker	Linkage and referral; information and education.	Outreach and in-reach. Duration varied across sites from 3–6 months, 6–9 months and open-ended.	No underlying theoretical framework or explanation of peer influence reported.
Myers JJ, 2018 (43).	Patient navigation	Clinical liaison and communication; practical support and material aid; coaching and skills building; advocacy.	Initial meeting in-jail upon release followed by in-community and accompaniment to medical, court and other appointments. Clients utilized 9 h per month in months 1 and 2 vs. 2.5 h per month from months 6 through 12).	Drawing from social support theory and patient-centered perspectives, peer enhance effects of program activities through role modelling, empathy, credibility and trust.
Odiachi A, 2020 (44). Sam-Agudu NA, 2017 (50). Sam-Agudu NA, 2017 (51). Sam-Agudu NA, 2018 (52).	Mentor or Expert Mother	Clinical liaison and communication; linkage and referral; information and education; coaching and skills building; emotional and social support.	Home visits every 2 weeks after linking with clients at clinic. Visits continued for 12 months after delivery of infants, with additional calls or visits in the event of missed clinic appointments.	Peers enhanced program activities through greater understanding and empathy. No underlying theoretical framework reported.
Pitpitan E V, 2020 (46).	Peer Navigation	Clinical Liaison and communication; coaching and skills building; linkage and referral; emotional and social support.	N/A	Incorporating elements of social support frameworks, peers enhance program activities through greater trust, credibility and empathy
Ryerson Espino SL (47)	Varied across study sites and locations: peer community; health outreach workers; patient navigators; peer educators; peer advocates; peer counsellors; promotoras; peer specialists; peer client assistants; peer lifeguards	Coaching and skills building; practical support and material aid; emotional and social support; advocacy.	Varied across site and locations. In-person sessions, accompaniment to appointments, outreach and phone contact described. Duration not reported.	Across a range of proposed programs and activities peers would empower and motivate desired health outcomes as role models. No underlying theoretical framework reported.
Reback CJ, 2019 (48). Reback CJ, 2019 (49).	Peer Navigation	Linkage and referral; coaching and skills building; practical support and material aid.	Unlimited in-person contact including accompaniment to appointments. The frequency of contacts titrated down after the first quarter of care.	Based on social learning theory, peers enhanced program activities as role models.
Steward WT, 2018 (53).	Peer navigation	Linkage and referral; coaching and skills building; information and education; clinical liaison and communication.	At least one in-person meeting and one check-in by text or phone for 4 months. Additional contacts were encouraged when needed.	Incorporating elements of social learning theory and social support frameworks, peers enhanced through role modelling and developing a high level of trust, credibility and understanding.