PrEPVacc HIV Vaccine Trial Halted Due to Potential Inefficacy, But Oral PrEP Regimens Continue

An HIV prevention study, PrEPVacc, evaluating the experimental vaccine regimens and a new form of oral pre-exposure prophylaxis (PrEP), has stopped further vaccinations due to the investigators determining there is little or no chance of the trial demonstrating efficacy in preventing HIV acquisition. The trial, running in East and Southern Africa and with over 1500 volunteer participants, was recommended by its independent data monitoring committee (IDMC) to stop the vaccination component of the study; however, the oral PrEP component will continue to completion.

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“Vaccinations to PrEPVacc trial participants have been stopped because an analysis of the data collected so far by our IDMC 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 trial director Eugene Ruzagira, PhD, senior scientist at Medical Research Council/Uganda Virus Research Institute and London School of Hygiene and Tropical Medicine, Uganda Research Unit, in a press release.

PrEPVacc is a series of 3 trials investigating 2 different combinations of HIV vaccines to determine if either are a successful method of preventing infection in populations who are at risk. Participants received injections of either 1 regimen combining a DNA vaccine with a protein-based vaccine; a regimen combining DNA, MVA, and a protein-based vaccine; or saline, a placebo. Study participants received 4 injections of each regimen or of the placebo.

Concurrently, PrEPVacc is testing a new oral PrEP drug formulation to determine if it is as effective as the currently approved formulations. Participants received study PrEP for up to 2 weeks after the third vaccine injection, and then were either provided non-study PrEP in a clinic or referred to access non-study PrEP at local service providers. Study participants also received information and counseling on how to best incorporate PrEP in combination with other available preventative methods against HIV acquisition.

A total of 1512 participants were healthy adults aged 18 to 40 years who reported behaviors at enrollment that make them more vulnerable to acquiring HIV. Almost all of the participants received oral PrEP, with only 6% deciding not to receive it. In addition, all but 10 participants had received 3 sets of vaccinations by October 2, 2023, and 1016 of the participants had received all 4 vaccinations. Vaccinations were stopped following the recommendation by PrEPVacc’s IDMC after a review on November 9, 2023.

“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…I have equally high hopes that an HIV vaccine will be developed 1 day…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.”

According to the investigators, follow-up of all participants will continue for additional safety data collection, HIV testing, and referral for ongoing care for 6 months after the final vaccine injection for all participants is given, or until the end of the oral PrEP trial concludes. The PrEPVacc trial had reviewed the participants twice a month, and no concerns regarding the safety of the vaccinations arose during its duration.

Reference

PREPVACC. Experimental HIV vaccine regimens likely to be ineffective in preventing HIV acquisition, PrEPVacc study reports. News release. December 6, 2023. Accessed December 13, 2023. https://www.eurekalert.org/news-releases/1010275