The only HIV vaccine in a late-stage trial has failed, researchers announced Wednesday, dealing a significant blow to the effort to control the global HIV epidemic and adding to a decadeslong roster of failed attempts.
Known as Mosaico, the trial was the product of a public-private partnership including the U.S. government and the pharmaceutical giant Janssen. It was run out of eight nations in Europe and the Americas, including the U.S., starting in 2019. Researchers enrolled nearly 3,900 men who have sex with men and transgender people, all deemed at substantial risk of HIV.
The leaders of the study decided to discontinue the mammoth research effort after an independent data and safety monitoring board reviewed the trial’s findings and saw no evidence the vaccine lowered participants’ rate of HIV acquisition.
“It’s obviously disappointing,” Dr. Anthony Fauci, the long-time director of the National Institute of Allergy and Infectious Diseases, said of the vaccine’s failure. However, he stated that “there are a lot of other approaches” that he finds promising early in the HIV vaccine research pipeline.
Fauci previously said he did not want to retire from the NIAID until an HIV vaccine had been proven at least 50% effective — good enough, in his view, for a global rollout. Instead, he retired from his post at the end of last month with this dream unfulfilled.
In addition to NIAID and Janssen, which is a division of Johnson & Johnson, the trial was run by the HIV Vaccine Trials Network, which is headquartered in the Fred Hutchinson Research Center in Seattle, and the U.S. Army Medical Research and Development Command.
Mosaico’s lack of efficacy was not unexpected, experts said, because of the recent failure, announced in August 2021, of a separate clinical trial, called Imbokodo, which tested a similar vaccine among women in Africa. Between the two trials, NIAID spent $56 million, according to an agency spokesperson.
The vaccines tested in both trials used a common cold virus to deliver what is known as mosaic immunogens, which were intended to trigger a robust and protective immune response by including genetic material from a variety of HIV strains prevalent around the world, according to the National Institutes of Health. Mosaico included an additional element intended to broaden the immune response.
Participants in Mosaico, who were between ages 18 and 60, received four injections over 12 months, either of the vaccine or a placebo. The monitoring board found no significant difference in the HIV acquisition rate between the two study groups.
