Unexpected Hives Observed in HIV mRNA Vaccine Trial

A recent safety evaluation of investigational HIV-1 trimer mRNA vaccines has revealed unexpected delayed urticaria, commonly known as hives, in a subset of participants. This phase 1, randomized, open-label clinical trial aimed to assess the safety and tolerability of three different HIV-1 mRNA vaccines: BG505 MD39.3 gp140, BG505 MD39.3 gp151, and BG505 MD39.3 gp151 CD4 knockout. Overall, the vaccines were found to be generally safe and well-tolerated.

However, 7% of the 108 participants, aged between 18 and 55 years, experienced delayed onset urticaria following vaccination. All affected individuals had previously received mRNA COVID-19 vaccines, and the hives appeared with each of the studied vaccines. Notably, four participants continued to experience intermittent urticaria even after 12 months. The reactions ranged from mild to moderate and included cases of generalized urticaria with dermatographism. Two cases involved delayed onset, making it the first time such reactions have been documented in this context.

The study documented adverse events such as lymphadenopathy, axillary pain, angioedema, and notably, urticaria. These reactions were observed regardless of the specific vaccine administered, suggesting a possible association with the mRNA platform itself. The precise mechanism behind these delayed urticarial responses remains unknown, but the findings emphasize the importance of ongoing monitoring and reporting of skin reactions in vaccine trials.

This research, conducted by teams funded by the National Institutes of Health, highlights both the potential and the challenges of mRNA technology in vaccine development. Despite these allergic reactions, the investigational vaccines demonstrated an acceptable safety profile, reinforcing the promise of mRNA platforms for future HIV vaccines and other therapeutics.

The full study and related editorial are published in the latest issue of the Annals of Internal Medicine. Continued investigation is necessary to understand the underlying causes of these reactions and to optimize safety strategies in vaccine development.

Source: https://medicalxpress.com/news/2025-04-unexpected-hives-reaction-trial-mrna.html