Table 5.

Primary health outcomes

Outcome area	Author, date, country (ref). design.	Reported outcomes
Linkage and retention in care	Adams J, 2020, USA (27). Pragmatic trial.	Decrease of no-show appointments over trial period. Peer navigator completed 10 home visits for missed appointments, resulting in 3 same or next-day appointments. Increased communication between members of the care team about the nuances of individual patient behaviour related to keeping appointments also reported.
	Cabral H, 2018, USA (28). RCT.	There was no evidence of difference between intervention and standard of care groups. There was a statistically significant improvement in retention in care for patients who were stably housed at baseline and those who completed all educational sessions in the intervention model. There was also a significant protective effect of increased face-to-face encounters by peers.
	Chang LW, 2015, Uganda (30). Randomised pragmatic trial.	Participants in the intervention arm who were care naïve at baseline were more likely to report being in care and enroll in care during follow up.
	Giordano TP, 2016, USA (31). RCT.	The peer mentoring intervention was no more successful in improving reengagement or retention in care than the control.
	Griffith D, 2019, USA (35). Pragmatic trial.	Higher risk youth living with HIV receiving intervention had better retention than standard of care in an adult clinic. Bi-directional communication with the peer navigator in the program, via either telephone or electronic message, decreased the risk of missed visits.
	Karwa R, 2017, Kenya (37). Mixed methods.	Patient enrolment was lower than estimates of HIV positive patients on ward, which may be due to implementation challenges. Unwanted disclosure was an issue for this program operating on a public ward, which peer navigators were reported to be skilled at overcoming. Counselling on stigma and disclosure were also reported to reduce refusal of linkage to care due to nondisclosure and fear of stigma.
	Lifson AR, 2017. Ethiopia (39). Panel/longitudinal.	No client was loss to follow up in the project, with positive client-reported outcomes supporting findings that intervention can improve retention in care.
	Maulsby C, 2015, USA (40). Panel/longitudinal.	Evidence of improvement reported, with 69% of participants retained in care at follow up. Older participants were more likely to be engaged and retained in care. Differences by race and gender in HIV care varied across programs, reflecting the diverse target populations, locations, and strategies employed by different sites.
	Monroe A, 2017, Uganda (41). Qualitative.	Qualitative results demonstrated plausible mechanisms through which peer support improved engagement in care to support findings from pragmatic trial.
	Minick SG, 2018, USA (42). Qualitative.	Peer mentoring was perceived as acceptable and impactful. Intervention was not likely to be intensive or broad enough to overcome stigma, low motivation and structural barriers to improving reengagement and retention in care, which may explain lack of effect reported in RCT.
	Myers JJ, 2018, USA (43). RCT.	Participants were more likely to be consistently engaged in HIV care relative to control group.
	Phiri S, 2017, Malawi (45). RCT.	Retention was higher in facility-based and community-based models compared with standard of care.
	Pitpitan EV, 2020, Mexico (46). Qualitative.	There was consensus that the program could improve ART coverage for key populations by helping to overcome geographic, transportation, and sociostructural barriers to HIV care. Police harassment, mobility, and non-HIV comorbidities were identified as challenges the program would need to navigate.
	Ryerson Espino SL, USA (47). Qualitative.	Out of ten sites all struggled to develop, and only five persisted through challenges to implement peer programs aimed at improving HIV linkage and retention initiative. The paper describes sites’ challenges and facilitators to develop, implement, and evaluate peer roles.
	Reback CJ, USA, 2019 (49). Panel/longitudinal.	Peer navigation combined with incentives was associated with significantly increased behaviours related to linkage and retention in HIV care.
	Reback CJ, 2019, USA (48). Panel/longitudinal.	Peer health navigation sessions were positively related to the number of HIV care visits for users of methamphetamine and any stimulant.
	Sam-Agudu NA, 2017, Nigeria (50). Non-randomised control trial.	Structured peer support significantly improved postpartum retention in care.
	Steward WT, 2018, South Africa (53). Mixed methods.	Program assessed as a feasible and acceptable approach for promoting engagement in care, with qualitative findings demonstrating mechanisms through which peer support assisted participants to overcome barriers to care related to stigma and discrimination, such as HIV disclosure.
Health service engagement	Chevrier C, 2016, India (31). Qualitative.	Findings provided detailed descriptions of how program activities intervened in discrimination, excluding participants from full participation in healthcare settings including ART centres, private and public hospitals.
Virological suppression.	Cabral H, 2018, USA (28). RCT.	No difference in viral load suppression between intervention and standard of care groups. For those who completed all educational sessions in the intervention model there was a suggestive improvement.
	Cunningham W, 2018, USA (32). RCT.	Intervention was successful at preventing declines in viral suppression, typically seen after release from incarceration, compared with standard transitional case management. The intervention was most effective at 12 months among the homeless and those who were virally suppressed at baseline.
	Giordano TP, 2016, USA (33). RCT.	The peer mentoring intervention was no more successful in improving virologic status than the control.
	Griffith D, 2019, USA (35). Pragmatic trial.	Improved retention in care did not to lead to improved virologic suppression.
	Hosseinipour M, 2017 Malawi (36) RCT.	Virological suppression did not differ according to treatment support arm.
	Maulsby C, 2015, USA (39). Panel/longitudinal.	Evidence of improvement reported with 46% of participants virally suppressed at follow-up. Older participants were more likely to be virologically suppressed.
	Minick SG, 2018, USA (42). Qualitative.	Peer mentoring was perceived as acceptable and impactful. Intervention was not likely to be intensive or broad enough to overcome stigma, low motivation and structural barriers to improving reengagement and retention in care, which may explain lack of effect on viral suppression reported in RCT.
	Myers JJ, 2018, USA (43). RCT.	There were no significant differences between groups in achieving undetectable viral load at study end or sustained suppression during the follow-up period.
	Reback CJ, USA, 2019 (49). Panel/longitudinal.	Peer navigation combined with incentives was associated with a significantly increased probability of achieving modest reductions in viral load and reaching and sustaining an undetectable viral load.
	Reback CJ, 2019, USA (48). Panel/longitudinal.	Peer health navigation sessions were positively related to reductions in viral load and reaching and sustaining an undetectable viral load for users of methamphetamine and any stimulant.
	Sam-Agudu NA, 2017, Nigeria (50). Non-randomised trial.	Structured peer support significantly improved rates of undetectable viral loads among women.
ART initiation and adherence	Cataldo F, 2017, Malawi (29). Qualitative.	Identified a need for patient education and psychosocial support with respect to the immediacy of ART initiation on the day of HIV diagnosis and disclosure to husbands and male partners. Participants were generally welcoming of peer support but concerned about confidentiality and stigma.
	Chang LW, 2015, Uganda (30). Randomised pragmatic trial.	No intervention effects were observed on ART initiation.
	Phiri S, 2017, Malawi (31).	ART uptake was higher in facility-based and community-based models compared with standard of care.
	Karwa R, 2017, Kenya (37). Mixed methods.	Providing medication refills for patients unwilling to disclose to medical teams and nurses was a clear need peer navigators met.
	Monroe A, 2017, Uganda (41). Qualitative.	Results identified challenges which explain lack intervention effect on ART initiation, including insufficient messaging surrounding ART initiation, lack of care continuity after ART initiation, rare breaches in confidentiality, and structural challenges.
	Graham SM, 2015, Kenya (34). Qualitative.	Describes the development of an adherence support intervention tailored for Kenyan MSM assessed as well tolerated, feasible, and acceptable in the pilot phase.
	Reback CJ, USA, 2019 (49). Panel/longitudinal.	Peer health navigation combined with incentives was associated with the sustainment of medication adherence to the achievement and maintenance of virological suppression.
	Reback CJ, 2019, USA (48). Panel/longitudinal.	Peer health navigation sessions were positively related to ART adherence to the achievement and maintenance of virological suppression for users of methamphetamine and any stimulant.
	Steward WT, 2018, South Africa (53). Mixed methods.	Program assessed as a feasible and acceptable approach for promoting ART adherence, with qualitative findings demonstrating mechanisms through which peer support assisted participants to overcome barriers to adherence related to stigma and discrimination such as HIV disclosure.
HIV prevention	Chang LW, 2015, Uganda (30). Randomised pragmatic trial.	Participants in the peer support intervention arm were more likely to report use of cotrimoxazole prophylaxis, and adherence to safe water vessel. No intervention effects were observed on bed net use, or condom use and number of sexual partners.
	Monroe A, 2017, Uganda (41). Qualitative.	Qualitative results demonstrated plausible mechanisms through which peer support improved use of cotrimoxazole prophylaxis and adherence to safe water vessel reported in pragmatic trial. Gender and employment reported as structural barriers to changing condom use and number of sexual partners.
	Myers JJ, 2018, USA (43). RCT.	Intervention successful in reducing sex that risks HIV transmission among participants compared with standard of care.
	Odiachi A, 2020, Nigeria (44). Mixed methods.	Attention to expert and mentor mothers’ coping skills and disclosure status, particularly to mentored clients is important to maximize the impact of peer support in prevention of mother to child transmission.
	Sam-Agudu NA, 2017, Nigeria (51). Non-randomised control trial.	Closely supervised, organized mentor mother support significantly improved presentation for early infant diagnosis among HIV-exposed infants in a rural Nigerian setting.
	Steward WT, 2018, South Africa (53). Mixed methods.	Program assessed as a feasible and acceptable approach for promoting HIV prevention, with qualitative findings demonstrating mechanisms through which peer support improved knowledge of condom use and addressed barriers to use of safer sex practices, such as HIV disclosure.
Community and social support engagement	Chevrier C, 2016, India (31). Qualitative.	Findings provided detailed descriptions of how peer-based approach provided a valued source of social support when discrimination excluded participation in families and communities, workplaces, and other HIV support groups and networks.
Cancer prevention	Koneru A, 2017, Tanzania (38). Cross-sectional.	Design and activities of a proposed peer navigation program was highly acceptable approach to address barriers to cervical cancer screening and treatment.
Alcohol and other drug risk behaviours	Myers JJ, 2018, USA (43). RCT.	No statistically significant differences in alcohol and drug use risk behaviour between treatment groups.