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Only Remaining HIV Vaccine Efficacy Trial Fails in Africa

The latest effort to develop an HIV (human immunodeficiency viruses) vaccine in Uganda, Tanzania and South Africa was halted on Dec. 6, 2023 after preliminary data showed that the vaccine would not be effective at preventing HIV infection. The PrEPVacc (pre-exposure prophylaxis vaccine) phase 2b trial was testing two different combinations of experimental HIV vaccines, including AIDSVAX, a DNA vaccine and CN54gp140.1 2 3 4 5 6 7 8

AIDSVAX was originally developed by biotechnology company Genentech, Inc. of San Francisco, California and subsequently tested by a Genentech offshoot, VaxGen, Inc. CN54gp140 was initially developed by Dr. Simon Jeffs of Imperial College London and subsequently manufactured by biopharmaceutical company Polymun Scientific GmbH of Vienna, Austria.9 10

“Last Roll of the Dice” for an HIV Vaccine This Decade

The trial has been described as “the last roll of the dice” for a generation of HIV vaccines, as it was the only remaining active HIV vaccine efficacy trial in the world.3 11

“In this decade, it will be the last roll of the dice. My prediction is there won’t be another efficacy study of an HIV vaccine until the 2030s” said Dr. Jonathan Weber, Dean of the Faculty of Medicine at Imperial College London.9

“We must look to a new generation of vaccine approaches and technology,” said Dr. Pontiano Kaleebu, chief investigator for PrEPVacc. “The development of a vaccine preventing HIV is a critical goal for Africa. It is a goal that must have even greater urgency now that no HIV vaccines are being trialed for efficacy anywhere in the world.”3 4 

“Little or No Chance” Vaccine Would Prevent HIV Infection

The trial, led by African researchers with support from 15 partner organizations (including Imperial College London), six from Africa, six from Europe and three from the United States, involved 1,512 healthy adults between 18 and 40 years of age, of which 87 percent were women. It had been scheduled to end in 2024, but it was prematurely terminated. Dr. Kaleebu said that the program’s independent data monitoring committee (IDMC) “recommended that even if we continue, we will not be able to show that the vaccine can be effective.”1 3 6

According to the trial’s director, Dr. Eugene Ruzagira:

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.6

Larry Corey, MD, virologist and principal investigator of HIV Vaccine Trials Network, based in Seattle, Washington, stressed the unusual difficulty in developing an HIV vaccine:

We’re doing something much harder with HIV than we did with COVID. COVID vaccines prevent you from getting sick; you still get infected. With HIV, you have to prevent someone from getting infected in the first place. And that requires way more antibody and a way better immune response.2

The trial has also been testing an oral PreP drug known as TAF/FTC (Descovy), designed to reduce the risk of contracting HIV. The IDMB has recommended continuing with that part of the trial.1 3

Final results of the vaccine components of the PrEPVacc trial are expected to be made available to the public this summer.6 8


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