The only HIV vaccine in a late-stage trial has failed. The grim news is a dampener for concerted HIV control efforts.

The announcement was made by involved researchers Wednesday, NBCNews reported. The vaccine trial of the product named Mosaico was a public-private partnership between the U.S. government and the pharmaceutical giant Janssen.

The trial, started in 2019, was conducted in eight countries in Europe and the Americas, including the U.S. Nearly 3,900 men who have sex with men and transgender people were recruited for the study and were all considered at increased risk of HIV.

An independent data and safety monitoring board looked at the trial’s results and found no link between the vaccine and the rate of HIV acquisition. Consequently, the researchers took the decision to discontinue their work.

“It’s obviously disappointing,” Dr. Anthony Fauci, ex-head of the National Institute of Allergy and Infectious Diseases (NIAID) and an integral partner in the trial, said, as per the news outlet. He added “there are a lot of other approaches” in the HIV-vaccine research field under consideration that he believes are promising.

“I don’t think that people should give up on the field of the HIV vaccine,” Fauci said.

This failure is not surprising, according to the experts. A similar vaccine in a separate clinical trial called Imbokodo also failed in August 2021. The vaccine was tested among women in Africa. NIAID had spent $56 million in total for the two trials, according to an agency spokesperson.

The vaccines in both trials used a common cold virus to deliver mosaic immunogens. The assumption was that the immunogen would trigger a robust immune response as it included genetic material from a mix of HIV strains prevalent around the world, according to the National Institutes of Health. Mosaico was one step ahead in that it included an additional element to widen the immune response.

In the Mosaico trial, participants between the ages of 18 and 60 were given four injections over a year. Following analysis, the monitoring board found no difference in the HIV acquisition rate between the two groups- vaccine and placebo.

The fact that the Mosaico vaccine elicited what are known as non-neutralizing antibodies against HIV and not neutralizing antibodies turned into its limitation, Fauci noted.

“It is becoming clear,” he said, “that vaccines that do not induce neutralizing antibodies are not effective against HIV.”

The trial’s failure is a “stark reminder of just how elusive an HIV vaccine really is and why this kind of research continues to be important,” Jennifer Kates, director of global health and HIV policy at Kaiser Family Foundation, said.

“Fortunately, there are a number of highly effective HIV prevention interventions already,” Kates added. “The challenge is to scale them up to reach all at risk.”