Background
STIs are common among participants participating in HIV vaccine trials. STIs may lead to proliferated immune responses, which could affect immune responses induced by HIV vaccines.
Methods
We conducted a secondary analysis of HVTN 705/HPX2008, a phase 2b placebo-controlled efficacy trial of Ad26.Mos4.HIV and aluminum phosphate-adjuvanted clade C gp140 in preventing HIV-1 infection in cisgender women aged 18 to 35 in Malawi, Mozambique, South Africa, Zambia and Zimbabwe. We calculated the baseline prevalence and incidence of the first occurrence of gonorrhea, chlamydia, trichomoniasis and syphilis or any STI between enrolment and 36 months and explored predictors of incident STIs using a multivariate Cox proportional hazards model. Baseline immune activation markers (T-cell, NK/ILC and DC panels) were compared among participants with and without baseline chlamydia infection by calculating weighted geometric mean ratios (GMR).
Results
In the MITT cohort of 2630 women, 841 (32.0%) had an STI at baseline. Of these, median age was 22 years (range: 18, 35) and most (82.4%) had secondary education. In the month prior, the median number of sexual partners was 2 (range: 0, 600) and sexual acts was 8 (range: 0, 800), with minimal (10.0%) consistent condom use. About half (47.8%) of participants exchanged sex for money/gifts and used alcohol during unprotected sex (43.2%) but most (94.1%) reported no prior STI. The incidence of any STI was 27.5% (95% CI: 25.7, 29.4) [chlamydia 17.4% (95% CI: 16.2, 18.7), gonorrhea 9.0% (95% CI: 8.2, 9.8), trichomoniasis 6.7% (95% CI: 6.1, 7.4), and syphilis 1.8% (95% CI: 1.5, 2.2)]. The cumulative incidence of any STI was 52.7% (95% CI: 50.3%, 55.0%) over 36 months. Lower risk of incident STIs was associated with increasing age (hazard ratio (HR): 0.92, 95% CI: 0.90, 0.94) and higher likelihood was associated with recent anal sex (HR: 1.54, 95% CI: 1.07, 2.21) and prior STI (HR: 1.65, 95% CI: 1.16, 2.35). No differences were observed in weighted GMR for a battery of baseline immune markers from women with and without baseline chlamydia except for CD123+ pDCs (weighted GMR = 1.23, 95% CI: 1.06, 1.43).
Conclusions
STIs were common among participants in HVTN 705/HPX2008. Risk of incident STIs was higher among women with recent anal sex or prior STI. Generally, Chlamydia infection does not appear to result in differences in baseline immune activation and should not alter immune responses to vaccination.