Scientific efforts to produce the world’s first HIV vaccine suffered another setback last week with the announcement that a late-stage clinical trial was discontinued due to lack of efficacy.

In a Jan. 18 news release, the National Institute of Allergy and Infectious Diseases revealed the Mosaico trial would be coming to an end. The trial, which consisted of 3,900 volunteers ages 18 to 60 in Europe, and North and South America, was ruled safe but ineffective by the NIH

Dr. Stephen Fallon, executive director of Latinos Salud, an HIV/AIDS service organization serving Broward and Miami-Dade Counties, said given the potency and easier dosing of today’s HIV medications it might seem surprising another vaccine trial produced disappointing results.

“The Mosaic vaccine tried to compensate for the failures of prior vaccines, by incorporating elements of multiple parts of the HIV virus, in hopes that the body’s immune system would recognize and respond to any of them that might find its way into a person’s bloodstream,” Fallon said. “The study also brought the subjects in multiple times to administer a total of four vaccine doses, which might have succeeded in rejuvenating a response that could otherwise wane.”

Participants in the regimen were transgender women and men who have sex with men and at risk for contracting the virus that causes AIDS. For ethical purposes, all participants had to be offered and had subsequently declined PrEP, the highly effective HIV prevention pill. 

While the process has helped in creating other vaccines that respond to new threats, namely COVID-19, creating an HIV vaccine may be the stiffest challenge science has faced, Fallon said.

“The fact that the enemy pathogen [HIV] takes up residence in the very immune system that vaccines need to leverage to create a defensive response [the immune system] makes this effort uniquely challenging,” Fallon said. 

The study, which launched in 2019, was a collaborative effort by Johnson & Johnson’s Janssen Pharmaceutical Companies, NIAID, and the U.S. Army Medical Research and Development Command. It was conducted at the Fred Hutchinson Cancer Research Center in Seattle. 

In 2021, the World Health Organization reported there were 38.4 million people living with HIV with 75% receiving antiretroviral therapy.

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