Menu

HIV vaccines tested in PrEPVacc fail to reduce infections

24 Jul 2024

The results of the PrEPVacc HIV vaccine trial show conclusively that neither of the two experimental vaccine regimens tested reduced HIV infections. These results were presented yesterday at the International AIDS Conference in Munich, Germany.

The PrEPVacc trial was carried out in Eastern and Southern Africa between 2020 and 2024. Vaccinations in the PrEPVacc trial were stopped in November 2023 when it became clear to independent experts monitoring the study data that there was little or no chance of the vaccines demonstrating efficacy in preventing HIV acquisition.

The results presented yesterday show more infections in the two vaccine arms than in the placebo arms. The researchers say they cannot draw a definitive conclusion about what this means because the statistical ‘confidence intervals’ for the comparison are wide, indicating a high degree of uncertainty.

The rate of HIV infection observed in the placebo group was lower than expected. This does not appear to be explained by a difference in the use of condoms or pre-exposure prophylaxis (PrEP) (which is known to be effective at preventing infections).

The trial took place across four sites in Masaka, Uganda; Mbeya and Dar es Salaam, Tanzania; and Durban, South Africa. 1,512 healthy adults aged 18-40 years who reported behaviours that made them more vulnerable to acquiring HIV took part in the study. Across all sites, 13% of participants were men, and 87% were women.

PrEPVacc tested two different combinations of HIV vaccines and compared each to a placebo (saline water) in a 1:1:1 randomisation. One regimen combined a DNA vaccine (DNA-HIV-PT123) with a protein vaccine (AIDSVAX), and the other combined the same DNA vaccine, a modified non dividing virus vector (MVA-CMDR) and a protein-based vaccine (CN54gp140). The schedule had four vaccine injection visits, three over approximately six months and a fourth a year after enrolment. 

In the primary vaccine analysis, of those who received at least three injections of the DNA/AIDSVAX combination, there was an incidence rate of 1.73 infections per 100 person years (95% confidence interval of 0.96 to 3.12) compared to 0.48 infections per 100 person years (95% confidence interval of 0.15 to 1.48) in the placebo group.

Of those who received the MVA-CMDR/CN54gp140 combination, there was an incidence rate of 2.38 infections per 100 person years (95% confidence interval of 1.24 to 4.57) compared to 0.51 infections per 100 person years (95% confidence interval of 0.13 to 2.02) in the placebo group.

These results mean that neither vaccine combination offered any protective effect, and the researchers say that the confidence intervals around the hazard ratios are so wide they cannot draw a definitive conclusion about what the higher number of infections in the vaccine arms means. They are discussing with other researchers further analyses that could help to explain the differences in HIV infection rates between the vaccine and placebo groups.

In advance of public release, PrEPVacc has begun sharing these results with the participants and communities who have been partners in the trial and will now inform individual participants which vaccine or placebo group they were in.

PrEPVacc also compared a new oral PrEP drug to the current standard PrEP drug. These results will be released later this year.

PrEPVacc is an African-led, European-supported HIV prevention project involving:

  • Medical Research Council / Uganda Virus Research Institute and London School of Hygiene and Tropical Medicine Uganda Research Unit, Uganda
  • Muhimbili University of Health and Allied Sciences, Tanzania
  • National Institute for Medical Research - Mbeya Medical Research Centre, Tanzania
  • HIV and other Infectious Diseases Research Unit, South African MRC, South Africa
  • Imperial College London, UK
  • Medical Research Council Clinical Trials Unit at University College London, UK
  • Centre Hospitalier Universitaire vaudois, Switzerland
  • Karolinska Instituet, Sweden
  • Medical Center of the University of Munich (LMU), Germany
  • International AIDS Vaccine Initiative (IAVI)
  • Africa Health Research Institute
  • EuroVacc Foundation
  • Gilead Sciences, Inc
  • Global Solutions for Infectious Diseases
  • East Virginia Medical School, CONRAD, USA
  • Military HIV Research Program at The Walter Reed Army Institute of Research (WRAIR)

The European & Developing Countries Clinical Trials Partnership (EDCTP) awarded a grant of €15M for the study and all the institutional partners are providing co-funding through staff salaries. Gilead Sciences, Inc is giving support to the project through materials, medicines, and funding. PrEPVacc is also supported by USAID and PEPFAR, USMHRP, SVRI, SAMRC, UKRI, the Wellcome Trust, the Bill and Melinda Gates Foundation, SIDA, and Bundesministerium für Bildung und Forschung (BMBF).

Further information