Placebo outperformed HIV vaccine tested in SA, Uganda, Tanzania, study results show

PrEPVacc promised to be a landmark trial towards a HIV vaccine when it was launched in 2020 but has since been halted. (Andrii Zorii/Getty Images)

• There was a higher rate of HIV infection among people who received PrEPVacc vaccine shots than among those who got a placebo, data released this week showed.
• The trial, in South Africa, Tanzania, and Uganda, was cancelled in November 2023 due to disappointing results.
• It was clear the vaccine did not work, its sponsor said.

A HIV vaccine test cancelled in November last year saw significantly higher rates of infection among those who received the shot compared to a placebo group, results made public this week show.

PrEPVacc promised to be a landmark trial towards a HIV vaccine when it was launched in 2020. But it was abruptly halted after a preliminary review. 

A team of African scientists assisted by European institutions made the results public at the 25th International AIDS Conference which is under way in Munich, Germany.

Independent experts determined “there was little or no chance of the vaccines demonstrating efficacy in preventing HIV acquisition”.

In one sample group of 532 participants, 11 who had received at least three shots were infected with HIV. Among those who received a placebo shot, only three got HIV.

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In a group that received a different vaccine combination, nine out of 244 participants got HIV, compared to two who had received a placebo.

“The vaccine questions posed in the trial have been answered. What we are clear about is that these vaccines won’t be taken any further,” said the PrEPVacc’s chief investigator, Professor Pontiano Kaleebu.

“We will continue to support our participants with counselling, testing and access to available prevention and care options,” said the Ugandan-based PrEPVacc’s trial director, Dr Eugene Ruzagira.

Although disappointed by the results, the researchers said they formed a base for future studies.

“The results have been surprising, and they have been disappointing. But that is science,” said Professor Sheena McCormack, the PrEPVacc project lead based at the Medical Research Council clinical trials unit at the University College London.

The study

A total of 1 512 high-risk adult participants, 87% of them women, were drawn from Durban, Masaka in Uganda, and Mbeya and Dar Er Saleem in Tanzania.

Two different combinations of HIV vaccines were tested against a placebo. 

The first combined a protein vaccine and a DNA vaccine. In the second, the same DNA vaccine was combined with a modified non-dividing virus vector and a protein-based vaccine.

The participants were given four injections within six months, then another injection once a year after enrolment.

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As the Covid-19 pandemic set in, there were changes in vaccine supply and recruitment of participants, and in June 2022 the research became based on the DNA and protein vaccine.

Professor Jonathan Weber of Imperial College London in the UK, the sponsor of PrEPVacc, said the results needed further analysis.

“While it is clear that the vaccines do not produce a protective effect, we are confronted by this most unexpected result in the placebo arm, where the extremely low incidence of HIV infection is at odds with the incidence found in our registration cohort.

“We need to await the results of further experiments to understand how this surprising set of results arose, if not by chance alone,” he added.

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