The first trial in Africa of two combination vaccines to prevent HIV has been halted after researchers concluded it was not working. The vaccines (part of the PrEPVacc study) were being tested on 1,500 people aged between 18 and 40 in Uganda, Tanzania and South Africa. The African-led trial, which began in December 2020, was stopped last month after an interim review of progress. The final results are expected to be made public in late 2024. The trial of a pre-exposure prophylaxis pill running alongside the vaccines tests will continue. Dr Eugene Ruzagira, trial director from the Uganda Virus Research Institute (UVRI) and assistant professor of epidemiology at the London School of Hygiene & Tropical Medicine, said: “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.” The PrEPVacc trials, led by African researchers with support from European scientists, tested two different combinations of HIV to see if either could prevent infection in populations particularly at risk of infection. The trials were funded with a €15m (£12.8m) grant from the EU’s European & Developing Countries Clinical Trials Partnership. Prof Jonathan Weber, from Imperial College London, one of the trial’s sponsors, said: “We do clinical trials because we don’t know the answer to questions. It was important to find out whether the combination vaccine regimens in PrEPVacc, developed over 20 years, should be ruled out or further developed for preventing HIV. “While we await the final results and analysis of individual products, I believe that 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 any success in protecting against HIV – the RV144 – developed in Thailand, was stopped in February 2020 after interim results found it was not working. Prof Pontiano Kaleebu, PrEPVacc’s chief investigator 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 have even greater urgency now that no HIV vaccines are being trialled 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 are living with HIV, more than 25 million in sub-Saharan Africa. Ruzagira told an Aids conference in Zimbabwe on Wednesday that he remained optimistic. “The scientific hurdles are high, but I have equally high hopes that an HIV vaccine will be developed one day,” he said. The RV144 vaccine was trialled in Thailand between 2003 and 2006, which after three years reduced infection rates by almost a third.