Experimental HIV Vaccine Regimen Safe but Ineffective

January 18, 2023 by Dan McCue
Experimental HIV Vaccine Regimen Safe but Ineffective
Transmission electron micrograph of HIV-1 virus particles (red) budding and replicating from a segment of a chronically infected H9 cell (blue). (NIAID photo)

WASHINGTON — An investigational HIV vaccine regimen tested among men who have sex with men and transgender people was safe but did not provide protection against HIV acquisition, an independent monitoring board has determined. 

The Phase 3 clinical trial for HPX3002/HVTN 706, or “Mosaico,” began in 2019 and involved 3,900 volunteers ages 18 to 60 years in Europe, North America and South America. 

Janssen Vaccines & Prevention B.V., sponsored the study with funding support from the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health. 

Based on the monitoring board’s recommendation, the study will be discontinued. Participants are being notified of the findings, and further analyses of the study data are planned.


The experimental vaccine regimen was developed by Janssen. It was based on “mosaic” immunogens — vaccine components featuring elements of multiple HIV subtypes — with the goal of inducing immune responses against a wide variety of global HIV strains. 

The investigational vaccine regimen consisted of four injections over a year of Ad26.Mos4.HIV. 

This vaccine candidate uses a common-cold virus (adenovirus serotype 26, or Ad26) to deliver the mosaic immunogens. 


The final two vaccinations were accompanied by a bivalent (two-component) HIV envelope protein formulation, combining clade C gp140 and mosaic gp140 envelope proteins, adjuvanted by aluminum phosphate to boost immune responses. All study vaccinations were completed in October 2022.

In its scheduled data review, the monitoring board determined there were no safety issues with the experimental vaccine regimen. 

However, the number of HIV infections were equivalent between the vaccine and placebo arms of the study. 

During the clinical trial, all participants were offered comprehensive HIV prevention tools, including pre-exposure prophylaxis, or PrEP.

Study staff ensured that participants who acquired HIV during the trial were promptly referred for medical care and treatment.

The Mosaico findings track with developments in the Phase 2b “Imbokodo” (HPX2008/HVTN 705) clinical trial, which was testing a similar HIV vaccine regimen in young women in sub-Saharan Africa. 


A monitoring board determined in 2021 that the experimental vaccine regimen in that study was also safe but ineffective in protecting against HIV acquisition.

Dan can be reached at [email protected] and at https://twitter.com/DanMcCue

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