We enrolled 801 participants between 24 January 2007 and 19 September 2007, before enrolment and vaccinations were discontinued, in five sites in SA (). Of those enrolled, 360 (44.9%) were women (), and two thirds (522) were under the age of 25. Nearly 20% (154) of participants had baseline Ad5 antibody titres ≤18 and 55.6% (445) had Ad5 antibody titres of >200. At enrollment, 129 men (29.3%) were circumcised (61 on the vaccine arm and 68 on the placebo arm). An additional 109 men were circumcised post-enrollment (52 vaccine, 57 placebo); half of these occurred pre-unblinding (26 vaccine, 29 placebo). HSV-2 prevalence at baseline was significantly higher in women than in men, (177/360=49.2% vs 72/441=16.3%, respectively, p<0.001). Baseline demographic and HIV risk behaviors were similar between study arms except for women reporting drinking or taking drugs during sex in the 6 months prior to screening (26/178=14.6% of vaccinees and 14/182=7.7% of placebo recipients, p = 0.04). Our cohort was predominantly heterosexual with 457/801=57.1% of participants reporting unprotected vaginal or anal sex as a risk factor. Men were more likely than women to report more than one sexual partner (247/441=56.0% vs 56/360=15.6%, respectively, p<0.001) and to report having a casual or anonymous partner (209/441=47.4% vs 40/360=11.1%, p<0.001). Most participants (304/441=68.9% of men and 302/360=83.9% of women) had a main partner, with 349/606=57.6% of those with a main partner regularly living apart. Less than 10% of both men and women reported having an HIV positive partner, exchanging sex for money or gifts, being forced to have sex, or being diagnosed with an STI and few women reported heavy drinking (). In total, 216 (27.0%) received one study injection, 529 (66.0%) two injections, and 56 (7.0%) three injections. There were no differences between the treatment arms in the number of injections received or in reasons for discontinuation of vaccination. Overall, 63 (7.9%) participants withdrew from the study by 31 August 2009 (), the proportion being similar between treatment arms. Post unblinding, more participants in the placebo vs vaccine arm (n=13 vs 6) refused further participation.
Participant baseline characteristics stratified by gender
Vaccines were well tolerated. Adverse events, local and systemic reactogenicity and in and pregnancies are reported in web appendix 3
. Self reported STI rates were similar between vaccine and placebo arms over the entire study period (7.5 vs 9.8 per 100 person-years) as well as over the pre- and post-unblinding periods (9.9 vs 9.6 and 7.7 vs 9.9 per 100 person-years). Women were more likely than men to report an STI (11.1 vs
6.7 per 100 person-years, p=0.007).
Reactogenicity symptomsa, Adverse Eventsb by study arm
At four weeks following the 2nd vaccination, 83/93=89.2% of vaccinees had developed an IFN-γ secreting T cell response to Clade B peptides and 72/93=77.4% to Clade C peptides (). For Clade B, Gag-specific responses were highest (74/93=79.6%); for Clade C, Pol-specific responses were highest (65/93=69.9%). All Clade C responders also had a Clade B response. Among responders to both Clades B and C, the overall magnitude of response to the Clade B vaccine-matched panel was significantly higher than to Clade C PTE panel; the same pattern held for responses to individual antigens (). Although not statistically different, vaccinees seronegative for Ad5 (titre ≤18) at baseline tended to demonstrate consistently higher response rates for both clades, overall and by gene, than those Ad5 seropositive (). Among responders, the Ad5 seronegative vaccinees also had a greater magnitude of response than those Ad5 seropositive for both clades overall (p = 0.004 for B and 0.007 for C), for Clade B Nef and Pol (p = 0.049 and = 0.002), and Clade C Pol (p = 0.01).
Interferon-γ secreting T cell responses by ELISPOT in vaccine recipients at Week 8
There was no evidence of VE (): the treatment HR adjusted for gender was 1.25 (95% CI: 0.76, 2.05). Accounting for the time at which participants were notified of their treatment assignment did not alter this finding: the HR adjusted for unblinding time was 1.15 (95% CI: 0.69, 1.90). The treatment HR was higher in the 6 months (26 weeks) after first vaccination, but this finding was not significant as can be seen in Web appendix Figure 1
which illustrates the log instantaneous HR for treatment over time since first vaccination. HIV incidence was similar between vaccine and placebo arms (4.54 vs 3.70/100 person-years, n=34 vs 28, Web appendix 1
). The majority of these infections were among women (n=42, ) with high HIV-1 incidence rates both in the vaccine arm (6.79) and placebo arm (5.86).
In multivariate Cox proportional hazard models, gender, age, HSV-2 and the interaction of gender and HSV-2 were significant predictors of HIV-1 infection (). Baseline Ad5 titre, categorized using either 18 or 200 as a cut-point, was not a significant predictor of HIV-1 infection and adjusting for Ad5 had little effect on the treatment HR; (HR= 1.24 – 1.31, depending on model). The number of vaccinations and behavioural risk factors were also not significant predictors of infection. Ad5 titre, gender, age or HSV-2 did not modify the treatment HR, nor did the effect of age and Ad5 titre differ by gender.
Risk factors for HIV-1 Infection
HSV-2 increased the risk of HIV-1 in men but not in women (). For men, HSV-2 increased the risk of infection more than 5-fold (5.23, 95% CI: 2.09, 13.10). For those HSV-2 negative at baseline, women had an increased risk of HIV-1 compared to men (HR 4.60; 2.16, 9.79). In an analysis restricted to women, there were no significant predictors of HIV-1 infection. In multivariable analysis for men (Web appendix Table 2
), HSV-2 (HR 4.90, 95% CI 2.03, 11.80) and having a main partner but living apart regularly (HR 3.61, 95% CI 1.31, 9.99) were associated with HIV-1 infection; neither Ad5 titre nor circumcision were significant. HSV-2 status post-enrollment was not assessed; among 31 participants who acquired HIV-1 who were HSV-2 seronegative at enrollment, 22 either did not change HSV-2 status (19) or acquired HSV-2 prior to HIV-1 infection (3), and all nine remaining participants were identified as HSV-2 and HIV-1 positive at the same visit.
Viral-load setpoint was calculated for 61 of the HIV-1 infected participants. One woman on the vaccine arm was excluded from the viral-load setpoint analysis because of a six month delay in confirming infection. There was no significant difference in the distribution of viral load setpoint between the vaccine arm (geometric mean titre 20,483 copies/mL, N=33) and the placebo arm (34,032 copies/mL, N=28) (, p=0.39, stratified by gender). Women tended to have lower viral-load setpoints than men (geometric mean 19,642 vs 45,438 copies/mL), which was not statistically significant (p = 0.15). Women who received vaccine (n=21) tended to have lower viral-load setpoints than women on the placebo arm (n=20) although this was not statistically significant (11,401 vs 34,773; p=0.16). Participants with baseline Ad5 titre > 18 (n=50) tended to have higher viral-load setpoint than those ≤ 18 (n=11), (31,924 vs 9,924), but this too, was not statistically significant (p =0.12).
Neither of the p
-values for the co-primary endpoints of HIV-1 infection and viral-load setpoint were statistically significant, adjusted p’s=0.39. Seven infected participants (3 vaccine, 4 placebo) started ART, all after the 3rd
month visit post HIV-1 diagnosis. Two women with CD4 counts above 350 initiated ART to prevent mother-to-infant transmission and data from these women were censored at 3 months and 1 year, respectively. Treatment was not a significant predictor of CD4 decline to less than 350 overall or among men, but among women, vaccinees were at significantly lower risk of this event than placebos: HR=0.33 (95% CI: 0.12, 0.91) (Web appendix Figure 2
). No other significant predictors of time to CD4 count less than 350 were found among baseline covariates considered: site, Ad5 titre, age quartiles, HSV-2 and their interactions with treatment.