The only HIV vaccine failed in advanced trials. What now?

The manufacturer of the only HIV vaccine still being tested in the final stages of clinical trials has declared it ineffective, marking another disappointment in a field that has long suffered from failure.

Dozens of HIV vaccine candidates have been tested and discontinued over the past few decades. Experts said the latest defeat sets back progress toward vaccine development by three to five years. However, other options may appear in early-stage trials to provide a powerful fortress against HIV.

The news is “disappointing, but not the end of efforts to develop a vaccine,” said Dr. Anthony Fauci, who led the National Institute of Allergy and Infectious Diseases until December, in an interview. “There are other strategic approaches.”

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An ongoing study called PrEPVacc in eastern and southern Africa is evaluating a combination of experimental HIV vaccines and preventative drugs. Scientists have made progress in developing powerful antibodies that can neutralize the virus. They are testing new vaccine technologies, including mRNA, against HIV.

However, the loss of the latter candidate highlights the challenges of designing a vaccine for an adversary as insidious as HIV. Four decades after its discovery, the virus still infects about 1.5 million people each year and kills about 650,000.

For people in rich countries, HIV is not the death sentence it once was. Strong drugs can suppress the virus in infected individuals. There are several options available for preventing infection: oral tablets and shots given every two months are already approved in the United States, for example, and the shot that only needs to be given every six months is in late-stage trials.

But these medicines must be taken for life, and are often inaccessible to those who need them most. A vaccine would be the perfect way to thwart the virus.

“The ultimate prevention method for any infection, especially a viral infection, is a safe and effective vaccine,” Fauci said. “This is why the field will continue to pursue very active research in this area.”

The now-defunct trial, called Mosaico, began in 2019 and is led by Janssen Pharmaceuticals, part of Johnson & Johnson. It tested the vaccine in 3,900 cisgender men (those always identified as male) and transgender individuals who have sex with straight men and transgender men, at more than 50 sites in nine countries in North America, South America and Europe.

The vaccine contains a mosaic of ingredients that aim to target several different subtypes of HIV that are found around the world. But the immune response it raised against the virus did not include large amounts of so-called neutralizing antibodies, which are the most powerful weapons against infection.

Fauci said that while the failure of the trial does not mean the end of the mosaic approach, it does suggest that a successful vaccine must awaken the body to produce broadly neutralizing antibodies.

After reviewing early data from the trial, an independent data and safety oversight board concluded that although the vaccine was safe, it did not prevent more HIV infections than a placebo. The board recommended that the company stop the experiment and inform the participants.

The finding didn’t entirely surprise experts, because a study of the same vaccine, called Imbokodo, was stopped in 2021. That trial tested the vaccine in sexually pregnant women in five sub-Saharan African countries.

The failure of the studies is particularly frustrating in part because they were funded by Johnson & Johnson, said Mitchell Warren, executive director of the HIV Prevention Organization (AVAC).

“It’s not about a lot of companies that are involved in infectious disease vaccines, so to see this not make it to market is a disappointment and a setback,” Warren said.

The news should prompt policymakers and activists to consider ways to make existing HIV prevention tools more widely available, he added.

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