HIV vaccine trial in Africa halted after disappointing initial results

Africa's first trial of two combination vaccines to prevent HIV has been halted after researchers concluded it did not work.

The pre-exposure prophylaxis vaccine (PrEPVacc) was tested on 1,500 people between the ages of 18 and 40 in Uganda, Tanzania and South Africa.

The African-led process, which began in December 2020, was halted last month after a mid-term review of progress. The final results are expected to be made public by the end of 2024.

Dr. Eugene Ruzagira, research director of the Uganda Virus Research Institute (UVRI) and assistant professor of epidemiology at the London School of Hygiene & Tropical Medicine, said: “Vaccinations for participants in the PrEPVacc trial have been halted due to an analysis of the data collected to date data by our independent data monitoring committee has led them to conclude that there is little or no chance of showing that the vaccines we are testing reduce the risk of HIV infection.”

The PrEPVacc trials, led by African researchers with support from European scientists, tested two different combinations of HIV to see if both could prevent infections in populations at particular risk of infection. The trials were funded by a €15 million (£12.8 million) grant from the EU Clinical Trials Partnership in Europe and Developing Countries.

A nurse in Masaka, Uganda, injects a trial participant with PrEPVacc. Stopping the trial means that no HIV vaccines are now being tested for efficacy anywhere in the world. Photo: L Dray/Getty

Professor Jonathan Weber, from Imperial College London, one of the study's sponsors, said: “We do clinical trials because we don't know the answers to the questions. It was important to find out whether the combination vaccine regimens in PrEPVacc, which have been developed over two decades, should be excluded or further developed for the prevention of HIV.

“While we await final results and analyzes of individual products, I believe our interim result puts this generation of putative HIV vaccines to bed,” he said.

Previous trials in South Africa to test the only vaccine that had shown some success in protecting against HIV – the RV144 – developed in Thailand, were halted in February 2020 after interim results showed it did not work.

Professor Pontiano Kaleebu, principal investigator of PrEPVacc at UVRI, said developing an effective vaccine to prevent HIV infection was “a critical goal for Africa”.

He said: “It is a goal that must be made even more urgent now that HIV vaccines are not being tested for efficacy anywhere in the world.

We have come so far in our HIV prevention journey, but we must look to a new generation of vaccine approaches and technology to take us forward again.”

About 39 million people worldwide living with HIV, more than 25 million in the part of Africa south of the Sahara.

Ruzagira told an AIDS conference in Zimbabwe on Wednesday that he remained optimistic. “The scientific hurdles are high, but I am equally hopeful that an HIV vaccine will one day be developed,” he said.

The RV144 vaccine was trialled in Thailand between 2003 and 2006, but after three years reduced the number of infections by almost a third.