Successful antiretroviral therapy (ART) treatment for people living with HIV/AIDS (PLHIV) is recognized as one of the most critical tools for HIV prevention. Indeed, evidence demonstrates that early ART initiation and optimal adherence improves clinical outcomes, prevents progression to AIDS, and effectively eliminates the onward transmission of HIV (; ; ; ). Recognizing this, UNAIDS’ “90–90-90” strategy for eliminating AIDS by 2030 () necessitates that by 2020, 90% of HIV-positive individuals are diagnosed, 90% of those infected are on treatment, and 90% on treatment are virally suppressed. The success of this strategy largely hinges upon high levels of ART adherence; however, in sub-Saharan Africa, on average only 73% of HIV-infected adults are ART adherent (), and in Eastern and Southern Africa an estimated 50% are virally suppressed (). These critical shortcomings underscore the need for new strategies to improve outcomes among PLHIV in order to reach “90–90-90”, and to ultimately end the HIV epidemic.

Transfer programs, which may include the short-term provision of cash and/or other types of in-kind (i.e. food) assistance, have been shown to be effective in improving patient outcomes in both high income and low- and middle-income countries (LMIC) (; ). Recently, such programs have emerged as an important strategy for improving HIV prevention (). For example, short-term cash transfers mitigated risky sexual behavior and risk of HIV infection among Tanzanian adults () and reduced prevalence of HIV infection among schoolgirls in Malawi (). A smaller but growing body of evidence demonstrates transfer effectiveness in improving outcomes for PLHIV: incremental cash transfers significantly increased uptake of, and retention in, prevention of mother-to-child transmission services among HIV-infected pregnant women in the Democratic Republic of Congo (), and food/cash transfers significantly reduced loss-to-follow-up (LTFU) and improved ART adherence amongst beneficiaries in Tanzania (). Overall, this literature suggests that transfers may be an important tool for reducing LTFU, increasing adherence, and ultimately improving outcomes for PLHIV in LMIC.

Considering this evidence base, however, it could be possible that transfer programs have heterogeneous effects. For example, they might be particularly effective for improving outcomes in vulnerable groups–like women, youth, and the poorest population members–who face immediate, largely economic, barriers to care. Indeed, empirical evidence demonstrates lack of economic resources as an important risk factor for ART non-adherence among women in South Africa () and HIV-infected youth in Uganda (). Transfer programs in LMIC have traditionally targeted the poorest population members, and have observed even among this sub-population the greatest health impacts in the “poorest of the poor” (; ). Consistently, beneficiaries of such programs have revealed that the costs associated with seeking and obtaining needed services often serve as the greatest barriers to HIV care (; ; ). Collectively, this literature implies that transfers could be an especially effective intervention within these vulnerable population subgroups.

Furthermore, it is largely unknown whether or for whom short-term transfers may engender sustained effects on clinical retention and ART adherence (; ). Providing transfers to recently diagnosed patients–a subgroup of individuals whose healthcare habits and identity surrounding their HIV status are still being formed ()–may be an important strategy for achieving long-term effects. However, although it is possible that this window of “new diagnosis” is a pivotal period within which it is possible to influence long-term behavior change, this has not been rigorously explored (; ).

Overall, a lack of conclusive evidence indicating whether transfers work differentially amongst subgroups in improving adherence and retention (; ; ) has led to a strong call for more research examining effect measure modifiers (EMMs) of potential interest (). Assessing differential effects may generate hypotheses regarding the mechanisms by which transfers work, providing clarity to a process that has been described as a “black box” (). Additionally, such studies may provide relevant information for settings where decisions must be made regarding how to best allocate finite resources (; ). Finally, the informed targeting of transfers to those for whom they work best can yield significant strides towards reaching “90–90-90”.

To address this gap, we conducted a secondary analysis of data from a recently concluded randomized trial in Shinyanga, Tanzania that investigated the effect of short-term cash or food transfers in improving ART adherence and retention among PLHIV (). The parent study found that both cash and food significantly and equivalently improved ART possession and reduced LTFU, and provided evidence suggesting long-term impacts associated with short-term transfers (). Here we evaluated the combined effect of the food/cash, collectively referred to as transfers, to determine whether their benefits differed by strata defined by sex, age, wealth, and time elapsed between HIV diagnosis and ART initiation.