HIV vaccines tested in PrEPVacc fail to reduce infections

23 July 2024 – The results of the PrEPVacc HIV vaccine trial conducted in Eastern and Southern Africa, which ran between 2020 and 2024, show conclusively that neither of the two experimental vaccine regimens tested reduced HIV infections among the study population.

Vaccinations in the PrEPVacc trial were stopped in November 2023 (and publicly announced in December 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 PrEPVacc vaccine trial results, announced today at AIDS 2024 in Munich, Germany, report more infections in the two vaccine arms than in the placebo arms, but the researchers say they cannot draw a definitive conclusion about what this means because the statistical ‘confidence intervals’ for the comparison are so wide, indicating a high degree of uncertainty.

The researchers also highlight that the rate of HIV infection observed in the placebo group was unusually low and does not appear to be explained by a difference in the use of condoms or pre-exposure prophylaxis (PrEP).

PrEPVacc is discussing with other groups worldwide further immunological analyses that could help to explain the differences in HIV infection rates between the vaccine and placebo groups.

Across South Africa, Tanzania and Uganda, the countries where PrEPVacc has conducted its trial, UNAIDS estimates that in 2022, a total of 10.7 million people were living with HIV and 244,000 adults and children were newly diagnosed with HIV. At the time its participants exited from the study, PrEPVacc was the only ongoing HIV vaccine efficacy trial in the world, and there are currently no other HIV efficacy trials underway or in the pipeline. PrEPVacc is the first HIV vaccine efficacy trial to be conducted in East African countries.

The PrEPVacc study, led by African researchers with support from European colleagues, is three trials in one. In its phase IIb exploratory efficacy trial, it tested two different vaccine regimens to see if either could prevent HIV infection in populations who may be vulnerable to acquiring HIV. During the period that participants received the first three vaccinations, a new form of oral pre-exposure prophylaxis (PrEP) was also tested against the existing standard for PrEP to see whether it was as effective at preventing HIV infections. PrEPVacc’s oral PrEP results are separate from the vaccine results and will be announced later in 2024.

Read the full press release here.