A 2012 systematic review and meta‐analysis including 13 studies enrolling 35 905 participants found inconclusive evidence on the effectiveness of vaginal microbicides [ 4 ]. Furthermore, a number of new vaginal microbicide trials have been published since 2012 [ 16 - 19 ]. To evaluate the current evidence on the effectiveness of vaginal microbicides in reducing the risk of HIV transmission in women, we conducted a systematic review and meta‐analysis.

Nonoxynol‐9 (N‐9), available as sponge, film or gel, is a non‐ionic surfactant spermicide [ 5 - 7 ] with in vitro activity against STIs such as Neisseria gonorrhoeae and Chlamydia trachomatis [ 8 ]. C31G (SAVVY) works by disrupting the outer membrane of the pathogenic organism, similar to N‐9 [ 9 , 10 ]. Cellulose sulphate (CS) is an entry inhibitor with in vitro activity against HIV‐1, Neisseria gonorrhoeae and Chlamydia trachomatis infections [ 11 , 12 ]. Carraguard creates a barrier between infected and non‐infected cells [ 13 ]. BufferGel protects against HIV infection by maintaining the normally acidic vaginal pH in the presence of ejaculate [ 14 ]. PRO2000 Gel inhibits viral attachment and entry into susceptible cells [ 14 , 15 ]. However, none of these early microbicides target HIV specifically [ 16 ]. The two latest microbicides, tenofovir [ 4 ] and dapivirine, are non‐nucleoside reverse‐transcriptase inhibitors with antiviral activity against HIV‐1 [ 17 , 18 ].

In order to control the HIV epidemic, prevention of new HIV infections remains critical. Pre‐exposure prophylaxis (PrEP) is a viable option; however, it requires strict adherence to taking oral pills daily [ 2 ]. While male condoms and circumcision have also been shown to effectively prevent HIV, reliance upon these male‐controlled methods offers women, who are more vulnerable, limited power to manage their own HIV protection. Other prevention methods include post‐exposure prophylaxis (PEP) and behavioural changes. Despite these options, preventing HIV acquisition and transmission remain a challenge among sexually active women. Perhaps a solution lies in microbicides, which the World Health Organization (WHO) defines as ‘compounds that can be applied inside the vagina or rectum to protect against sexually transmitted infections (STIs) including HIV’ [ 3 ]. Vaginal microbicides are a potential female‐controlled biomedical intervention for preventing HIV [ 4 ], especially where women are unwilling or unable to negotiate condom use.

In 2017, an estimated 36.9 million people were living with HIV, 1.8 million were newly infected, and 940 000 died from HIV/AIDS‐illnesses. During the same year, about 1000 adolescent girls and young women (AGYW), aged 15–24 years, were being newly infected with HIV every day. In sub‐Saharan Africa, AGYW were twice as likely to be living with HIV as men, and 75% of new infections among 15‐ to 19‐year‐old adolescents were in girls [ 1 ].

We performed random‐effects meta‐analysis of risk ratios separately for individual microbicides using the Mantel–Haenszel method in Review Manager 5.3 software [ 23 ] using the number analysed as the denominators to avoid data imputation. To assess the extent and significance of heterogeneity, we used the I 2 test statistic and the chi‐squared test ( P < 0.1 indicated statistical significance) [ 20 ]. Clinical heterogeneity and differences in the composition and mechanism of action of the various microbicides rendered it inappropriate to calculate an overall effect in a meta‐analysis. Rather, we analysed the different microbicides by subgroups. We assessed publication bias by inspecting the funnel plot for symmetry. We also summarised the certainty of evidence in a summary of findings table (Table 2 ) using the GRADE approach to evaluate the quality of evidence for each outcome (HIV incidence) as ‘high’, ‘moderate’, ‘low’ and ‘very low’ based on risk of bias among included studies, indirectness of evidence, unexplained heterogeneity or inconsistency of results, imprecision of results (i.e. wide confidence intervals) and high probability of publication bias [ 24 ].

The same review authors independently assessed each included study for risk of bias using the Cochrane risk of bias tool [ 20 ] with respect to sequence generation, allocation concealment, blinding, incomplete outcome data, selective reporting and other potential sources of bias. For each included study, both reviewers independently rated each domain at either ‘low’, ‘high’ or ‘unclear’ risk of bias. Any disagreements were resolved through discussion between the two review authors and consultation with a third review author (SAA), who was blinded to the others’ judgements.

Two independent review authors (AM and SAA) screened potentially relevant titles and abstracts according to pre‐specified eligibility using Covidence software [ 22 ]. Full‐text articles of records included after title and abstract screening were retrieved for further re‐screening. Disagreements arising from record screening were resolved through discussion.

To identify reports relevant to our review, we conducted a comprehensive search of the PubMed and EMBASE databases, irrespective of language, for eligible studies published before 4 June 2019. The PubMed search strategy is given in Appendix S1 , and the same strategy was adapted for EMBASE. We used various combinations of the following search terms and key words: “microbicides”, “vaginal”, “HIV”, and “RCT”. We also searched the reference lists of included studies as well as clinical trial registries to identify any further eligible studies or ongoing trials. We corroborated our included studies with those included in the previously published systematic review [ 4 ].

The main outcome of interest was effectiveness of vaginal microbicides, assessed as risk of HIV infection in the intervention group compared with the control group. We compared HIV risk between the microbicide and control groups using risk ratios (RR).

Experimental interventions with any vaginal microbicide such as N‐9 sponge/film/gel, CS gel, SAVVY gel, Carraguard gel, BufferGel, PRO2000 gel, tenofovir gel or intravaginal ring with dapivirine were included; eligible controls were placebo gel or no gel.

All randomised controlled trials (RCTs) assessing effectiveness of any vaginal microbicide in reducing HIV transmission among women were eligible for this systematic review. We excluded phase I trials and pharmacokinetics studies as well as studies conducted in vitro or in non‐human models such as macaques. We also excluded other studies if they did not involve a vaginal microbicide designed to prevent HIV; for example, studies testing rectal microbicides, contraceptives, PrEP or prevention of other STIs. Eligible participants were healthy, sexually active, non‐pregnant, HIV‐negative women of reproductive age.

We followed the Cochrane methodology guidelines [ 20 ] and the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) checklist [ 21 ] in conducting this systematic review.

Results

Results of the search Our electronic database search on 4 June 2019 yielded a total of 4468 records. After removing 395 duplicates, we screened 4073 titles and abstracts according to predetermined eligibility criteria. Of the records screened, we excluded 4033 that did not meet eligibility criteria for this review. A total of 40 full‐text articles that met eligibility criteria were retrieved for further screening, of which 22 articles were excluded for various reasons (ten did not measure HIV outcome, six were not RCTs, three were conference abstracts, and three were letters to the editor). Overall, 18 studies that met eligibility criteria were included in the review. (Figure 1). Figure 1 Open in figure viewer PowerPoint Search yield for studies assessing effectiveness of vaginal microbicide trials for HIV prevention.

Participants, settings and interventions The characteristics of 18 included studies [5-19, 25-27] are summarised in Table 1. Studies were conducted from 1987 to 2015, assessed eight different microbicides and enrolled a total of 40 048 healthy, sexually active, non‐pregnant and HIV‐negative women. Studies were conducted mainly in sub‐Saharan Africa (South Africa [8, 11, 13-19, 26, 27], Uganda [11, 15, 17-19], Zimbabwe [14, 18, 19], Benin [8, 11], Cameroon [6, 7], Côte d’Ivoire [8], Ghana [10], Kenya [5, 25], Malawi [14, 18], Nigeria [9, 12], Tanzania [15] and Zambia [14]), as well as in Asia (India [11] and Thailand [8]), and the USA [14] (Figure 2). Seven studies were multi‐country [8, 11, 14, 15, 17-19]. Three early studies that enrolled female sex workers were conducted in Kenya [5, 25] and Cameroon [6]. Participants were at least 16 years of age at the time of enrolment. Table 1. Characteristics of 18 included RCTs evaluating vaginal microbicides for the prevention of HIV transmission Study ID Year Country Participants enrolled Participants age (years) Microbicide and delivery method Trial discontinued Kreiss 1992 [ 5 1987–1990 Kenya 138 Female Sex Workers NR N‐9 sponge (peri‐coital) Yes Roddy 1998 [ 6 1994–1996 Cameroon 1292 Female Sex Workers 18–45 70 mg N‐9 Film (peri‐coital) No Richardson 2001 [ 25 1996–1998 Kenya 278 Female Sex Workers 18–48 52.5 mg N‐9 gel (peri‐coital) Yes Van Damme 2002 [ 8 1996–2000 Benin, Côte d’Ivoire, South Africa, and Thailand 892 Sexually active women 16+ N‐9 (COL‐1492) gel (peri‐coital) No Roddy 2002 [ 7 1998–2000 Cameroon 1251 Sexually active women 18+ N‐9 gel (peri‐coital) No Carraguard Phase II South Africa Team 2010 [ 26 1999–2002 South Africa 400 Sexually active women 18+ Carraguard gel (peri‐coital) No Peterson 2007 [ 10 2004–2006 Ghana 2142 Sexually active women 18–35 SAVVY Gel (peri‐coital) Yes Feldblum 2008 [ 9 2004–2006 Nigeria 2153 Sexually active women 18–35 SAVVY Gel (peri‐coital) Yes Halpern 2008 [ 12 2004–2007 Nigeria 1644 Sexually active women 18–35 CS gel (peri‐coital) Yes Van Damme 2008 [ 11 2005–2007 Benin, India, South Africa, and Uganda 1428 Sexually active women 18+ CS gel (peri‐coital) Yes Skoler Karpoff 2008 [ 13 2004–2007 South Africa 6202 Sexually active women 16+ Carraguard gel (peri‐coital) No Abdool Karim 2011 [ 14 2005–2009 Malawi, South Africa, Zimbabwe, Zambia, and USA 3101 Sexually active women 18+ 0.5% PRO2000 gel and BufferGel (peri‐coital) No McCormack 2010 [ 15 2005–2008 South Africa, Tanzania, Uganda, and Zambia 9385 Sexually active women 16+ 2% PRO2000 and 0.5% PRO 2000 gels (peri‐coital) Yes Abdool Karim 2010 [ 27 2007–2010 South Africa 1085 Sexually active women 18–40 tenofovir gel (BAT‐24) No Marrazzo 2015 [ 19 2009–2012 South Africa, Uganda, and Zimbabwe 2010 Sexually active women 18–45 tenofovir gel (daily) Yes Delany‐Moretlwe 2018 [ 16 2011–2014 South Africa 2059 Sexually active women 18–30 tenofovir gel (BAT‐24) No Nel 2016 [ 17 2012–2015 South Africa and Uganda 1959 Sexually active women 18–45 dapivirine ring (monthly insertion) No Baeten 2016 [ 18 2012–2015 Malawi, South Africa, Uganda, and Zimbabwe 2629 Sexually active women 18–45 dapivirine ring (monthly insertion) No Figure 2 Open in figure viewer PowerPoint Map showing geographic regions from which the 18 included studies assessing effectiveness of vaginal microbicides for prevention of HIV transmission were conducted. Eight interventions (vaginal microbicides) were examined: N‐9 [5-8, 25], SAVVY Gel [9, 10], CS [11, 12], Carraguard [13, 26], 0.5% PRO2000 [14, 15] and 2% PRO2000 [15], BufferGel [14], tenofovir [16, 19, 27] and dapivirine intravaginal ring [17, 18]. The method of delivery was mostly peri‐coital except for one tenofovir study where the gel application was daily [19], two tenofovir studies with before and after application [16, 27] and the dapivirine intravaginal ring which was self‐inserted once per month [17, 18]. Eight studies were stopped early due either to lack of effectiveness [5, 9, 10, 15, 19], safety concerns [11, 12], or slow enrolment and concerns about follow‐up rates [25].

Comparisons and outcomes The primary comparison was microbicide agent against placebo. One study compared condoms plus N‐9 gel with condoms only [7], while the other 17 studies compared microbicide gel with either placebo gel or no gel. Three studies had more than two treatment arms: McCormack et al. [15] assessed both 2% PRO2000 and 0.5% PRO2000 vs. placebo. To avoid double‐counting women in the placebo group in the meta‐analysis, we split the placebo group into two and compared each intervention arm with half of the placebo group. Abdool Karim et al. [14] assessed BufferGel and 0.5% PRO2000 gel vs. placebo gel and no gel group; we compared the BufferGel vs. no gel group and 0.5%PRO2000 gel vs. placebo gel for consistency with the McCormack et al. trial [15] that also compared 0.5%PRO2000 with placebo gel. Marrazzo et al. [19] compared oral tenofovir disoproxil fumarate (TDF), oral tenofovir–emtricitabine (TDF‐FTC), oral placebo, vaginal tenofovir gel and vaginal placebo gel; we chose the latter two treatment groups as they were the only ones relevant to this review. The outcome evaluated was the risk of HIV infection between the two groups.

Risk of bias of included studies Figure 3 shows the risk of bias assessments for each of the included trials. We judged most studies to be at low risk of selection bias. All 18 included studies used adequate random sequence generation via computer‐generated random numbers with most using block randomisation. Sixteen studies used either central allocation and/or sequentially numbered, sealed opaque envelopes to assign participants to different treatment groups. Two studies [5, 25] did not describe how treatment allocation concealment was performed. Figure 3 Open in figure viewer PowerPoint Risk of bias graph for 18 included studies assessing effectiveness of vaginal microbicide trials for prevention of HIV transmission. Overall, we judged studies to be at low risk of performance and detection bias. Sixteen studies used adequate blinding of participants and personnel. However, blinding was not possible in two studies [5, 7] because a placebo product of matching material was not available at the time when the studies were conducted. Fifteen studies adequately blinded laboratory staff who assessed the HIV status of participants and were therefore judged at low risk for detection bias. However, three studies [5, 17, 25] did not report whether outcome assessors were masked and thus were judged as unclear for detection bias. Overall, we judged studies to have low risk of attrition bias since 16 studies carried out intention‐to‐treat (ITT) analyses and had minimal loss to follow‐up of less than 20%, with similar loss to follow‐up rates between treatment groups. In one study [25], number lost to follow‐up was unclear and in another [5] the analysis was not ITT. Overall, we judged studies to have low risk of reporting bias since 13 studies had publicly available protocols from which we verified that all the pre‐specified outcomes were reported in the manuscripts. The earlier published five studies [5-8, 25] were judged as unclear for risk of selective outcome reporting as they did not have publicly available protocols for comparison. Overall, we judged the studies to have unclear risk of potential sources of other bias as seven studies were stopped early [5, 10-12, 15, 19, 25] which might have reduced statistical power to detect any differences in outcome. The remaining nine studies appeared to be free of other bias.

HIV incidence We performed random‐effects meta‐analysis and calculated effect estimate by microbicide subgroups, without pooling all studies in an overall meta‐analysis (Figure 4). Figure 4 Open in figure viewer PowerPoint Forest plot showing meta‐analysis of studies assessing vaginal microbicides for prevention of HIV transmission. The GRADE Summary of Findings (SoF) Table is given in Table 2. Table 2. GRADE Summary of Findings Table for studies assessing vaginal microbicides for prevention of HIV transmission Summary of findings: Vaginal microbicide compared to Placebo for HIV Prevention Patient or population: Healthy, sexually active, HIV‐negative, non‐pregnant women of reproductive age Setting: Studies conducted mainly in sub‐Saharan Africa Intervention: Vaginal microbicide Comparison: Placebo Outcomes Anticipated absolute effects* (95% CI) Relative effect (95% CI) No of participants (studies) Certainty of the evidence (GRADE) Risk with Placebo Risk with Vaginal microbicide HIV Incidence – nonoxynol‐9 74 per 1000 85 per 1000 (69–105) RR 1.15 (0.93–1.42) 3554 (5 RCTs) ⨁⨁◯◯ LOWa,b HIV Incidence – Cellulose sulphate 20 per 1000 23 per 1000 (12–44) RR 1.16 (0.61–2.21) 2904 (2 RCTs) ⨁⨁◯◯ LOWa,b HIV Incidence – SAVVY 10 per 1000 14 per 1000 (7–26) RR 1.34 (0.69–2.59) 4119 (2 RCTs) ⨁⨁◯◯ LOWa,b HIV Incidence – Carraguard 50 per 1000 44 per 1000 (35–55) RR 0.89 (0.71–1.10) 6405 (2 RCTs) ⨁⨁◯◯ LOWa,b HIV Incidence – 0.5% PRO2000 49 per 1000 43 per 1000 (29–62) RR 0.88 (0.60–1.28) 6236 (2 RCTs) ⨁⨁◯◯ LOWa,b HIV Incidence – 2% PRO2000 39 per 1000 32 per 1000 (23–44) RR 0.81 (0.58–1.12) 4147 (1 RCT) ⨁⨁◯◯ LOWa,b HIV Incidence – BufferGel 70 per 1000 71 per 1000 (49–102) RR 1.02 (0.71–1.46) 1526 (1 RCT) ⨁⨁◯◯ LOWa,b HIV Incidence – tenofovir 79 per 1000 66 per 1000 (51–84) RR 0.83 (0.65–1.06) 4864 (3 RCTs) ⨁⨁◯◯ LOWa,b HIV Incidence – dapivirine Ring 78 per 1000 56 per 1000 (45–70) RR 0.71 (0.57–0.89) 4564 (2 RCTs) ⨁⨁⨁◯ MODERATEa We report the results separately for each microbicide below. The funnel plot (Figure 5) is not suggestive of publication bias. Figure 5 Open in figure viewer PowerPoint Funnel plot showing the likelihood of publication bias among included studies assessing effectiveness of vaginal microbicides in preventing HIV transmission.

Nonoxynol‐9 Five studies [5-8, 25] compared N‐9 to placebos (or condoms in one study [7]). At a follow‐up period ranging from three to five years, N‐9 compared with controls showed no evidence of effect on HIV risk, as indicated in a meta‐analysis of five RCTs involving 3554 participants (RR 1.15, 95% CI: 0.93–1.42, Figure 4). There was low statistical heterogeneity between studies (I2 = 0%), and the certainty of evidence was low; we downgraded one level for imprecision due to wide confidence intervals and one level for indirectness since the studies were done mostly in Africa and results may not be generalisable globally (Table 2).

SAVVY gel Data were available from two studies that compared SAVVY gel vs. placebo [9, 10] and each found no evidence of effect in reduction of HIV risk. At four years follow‐up, meta‐analysis (2 RCTs, 4119 women) suggests no evidence of a difference in HIV risk between SAVVY gel and placebo (RR 1.34, 95% CI: 0.69–2.59, Figure 4). There was low heterogeneity (I2 = 24%) and the certainty of evidence was low, downgrading one level each for imprecision and indirectness (Table 2).

Cellulose sulphate (CS) gel Two studies assessed CS gel vs. placebo [11, 12] at three to four years follow‐up. A meta‐analysis (2 RCTs, 2904 women) found that compared with placebo, CS gel had no evidence of benefit in reducing the risk of HIV infection (RR 1.16, 95% CI: 0.61 to 2.21, Figure 4). Statistical heterogeneity between studies was low (I2 = 39%). We graded the certainty of evidence as low after we downgraded one level each for imprecision and indirectness (Table 2).

Carraguard gel Carraguard gel was evaluated in two studies (6405 women). Investigators compared Carraguard gel vs. placebo [13, 26]. At a follow‐up of three years, a meta‐analysis of the two studies suggests no evidence of effect in reduction of HIV risk (RR 0.89, 95% CI: 0.71–1.10, Figure 4). There was low heterogeneity (I2 = 0%) and low certainty of evidence, downgrading one level each for imprecision and indirectness (Table 2).

Buffer gel One study assessed Buffer gel compared to no gel use among 1526 women at four years follow‐up [14]. Point estimates suggest that Buffer gel, compared to no gel use, had no evidence of effect on HIV risk reduction (RR 1.02, 95% CI: 0.71–1.46, Figure 4). Certainty of evidence was low, as we downgraded one level each for imprecision and indirectness (Table 2).

PRO2000 Data on two studies [14, 15] involving 6236 women examined the effect of 0.5% PRO2000 gel compared with placebo on risk of HIV transmission. At a follow‐up of four years, meta‐analysis suggests that 0.5% PRO2000 gel compared to placebo had no evidence of effect in reduction of HIV risk (RR 0.88, 95% CI: 0.60–1.28, Figure 4). Statistical heterogeneity between studies was moderate (I2 = 55%), and the certainty of evidence was low; we downgraded one level each for imprecision and indirectness (Table 2). One study [15] enrolled 4147 women and compared 2% PRO2000 gel with placebo. At a follow‐up of three years, point estimates showed no evidence of effect in reduction of HIV risk (RR 0.81, 95% CI: 0.58–1.12, Figure 4). Certainty of evidence was low; we downgraded one level each for imprecision and indirectness (Table 2).

Tenofovir Gel Of the three studies assessing tenofovir 1% gel vs. placebo gel [16, 19, 27], one study [27] found statistically significant 37% reduction in HIV risk (RR 0.63, 95% CI: 0.43 to 0.93, 843 women) in favour of tenofovir gel. However, a meta‐analysis of the three studies (4864 women) with follow‐up of four years indicates no evidence of effect in reduction of HIV risk (RR 0.83, 95% CI: 0.65–1.06, Figure 4). Statistical heterogeneity between studies was low (I2 = 33%), and the certainty of evidence was low. We downgraded one level each for imprecision and indirectness (Table 2).