PrEPVacc tested two different combinations of vaccines to determine whether either can prevent HIV infection in populations at risk of acquiring the virus.

PrEPVacc has announced they will be shutting down their study of experimental HIV vaccine regimens and a new form of oral pre-exposure prophylaxis (PrEP) running in East and Southern Africa. Despite having 1,500 participants enrolled in the program, the company believes there is little to no chance of the trial demonstrating vaccine efficacy in preventing HIV acquisition based on the recommendation of its independent data monitoring committee (IDMC).1

Led by African researchers, PrEPVacc is considered to be three trials in one. The company focuses on testing two different combinations of HIV vaccines to find out whether either can prevent HIV infection in populations at risk of acquiring HIV, with participants receiving injections of either one regimen combining a DNA vaccine with a protein-based vaccine (AIDSVAX), a regimen combining DNA, MVA and a protein-based vaccine (CN54gp140), or a placebo (saline).1

Despite the cancellation, full results of the vaccine trial will not be known until all the study visits have been completed, which the study teams aim to do by June 2024. Full results will be analyzed and shared with participants, study teams, and the public in the second half of 2024.1

“Vaccinations to PrEPVacc trial participants have been stopped because an analysis of the data collected so far by our Independent Data Monitoring Committee has led them to conclude that there is little or no chance of demonstrating that the vaccines we are testing are reducing the risk of acquiring HIV,” said Eugene Ruzagira, PrEPVacc’s trial director, in a press release. “PrEPVacc clinicians and scientists will not know the vaccine trial’s full results until after June 2024, when the collection of all the trial data is complete, and they can be analyzed. A report will be available in the later months of 2024.”

According to a study by KFF, Sub-Saharan Africa is home to two-thirds of people living with HIV globally and is considered the hardest hit region in the world. Although testing capacity has increased in recent years, giving people the ability to learn their HIV status, the study estimates that approximately 14% of those affected with HIV are still unaware.2

Beginning back in June, investigators moved into the post-recruitment phase of the trial. Before being discontinued, PrEPVacc was the only HIV vaccine efficacy trial to be conducted anywhere in the world. Furthermore, it was also the first HIV vaccine efficacy trial to be conducted in East African countries. Before PrEPVacc, investigators conducted a preliminary preparedness study titled Registration Cohort, which consisted of local people joining a community advisory board or community working group and, on behalf of study participants and the community, raised concerns about rates of HIV infection and PrEP rollout to investigators.3

“The scientific hurdles are high, but I have equally high hopes that an HIV vaccine will be developed one day,” continued Ruzagira. “Every day, all around the world, important research like PrEPVacc is moving us forward, and participants are willing to step forward with us and make a difference to the health of their communities.”


1. Experimental HIV vaccine regimens likely to be ineffective in preventing HIV acquisition, PrEPVacc study reports. EurekAlert. December 6, 2023. Accessed December 7, 2023.

2. The Global HIV/AIDS Epidemic. KFF. July 26, 2023. Accessed December 7, 2023.

3. Investigators Advance PrEPVacc Trial To Evaluate HIV Vaccine Efficacy. Pharmacy Times. June 13, 2023. Accessed December 7, 2023.

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