mRNA-1608 Herpes Vaccine Clinical Trials, Dosage, Indication, News, Side Effects

Moderna Inc.'s herpes simplex virus (HSV) vaccine candidate, mRNA-1608, is a Messenger RNA (mRNA) vaccine targeting HSV-2 disease. On February 18, 2022, Moderna Inc. stated that it expects an HSV-2 vaccine could provide cross-protection against HSV-1. With mRNA-1608, Moderna aims to induce a strong antibody response that combines neutralizing and effector functionality with cell-mediated immunity. In clinical trials, a prophylactic genital herpes vaccine should prevent HSV-1 and HSV-2 genital lesions and infection of the dorsal root ganglia, the site of latency. Additionally, vaccine immunity should be durable for decades, possibly without the need for booster doses. While these efficacy goals have been elusive from previous herpes vaccine candidates, new efforts with nucleoside-modified mRNA-lipid nanoparticle vaccines show great promise. 

Moderna is developing mRNA-1608 to reduce the burden of HSV lesions, leveraging mRNA technology that offers potential advantages in efficacy, speed of development, and production scalability and reliability. This may position our company as a leader in preparing for and responding to infectious disease threats that place millions of people at risk worldwide. To further characterize Moderna's IM vaccines, biodistribution studies were conducted to demonstrate where mRNA goes in the body after injection. Studies indicate that injected mRNA remains predominantly at the injection site and nearby draining lymph nodes. Furthermore, consistent with its transient nature, mRNA is undetectable in the body five days after injection, with minimal mRNA detectable after only three days.

A Phase 1 clinical study of mRNA-1608 in Healthy Adults Aged 18 to 55 with recurrent genital herpes caused by HSV-2 began recruiting participants on September 6, 2023. On March 27, 2024, Moderna confirmed the first-in-human, fully enrolled Phase 1/2 clinical trial (NCT06033261) of mRNA-1608, which includes three hundred participants with a history of recurrent genital herpes, randomly assigned in a 1:1:1:1 ratio to receive mRNA-1608 at one of the three dose levels or control (BEXSERO) administered as two doses at 0 and 2 months (Day 1 and Day 57). This study (mRNA-1608-P101) aims to generate safety and immunogenicity data and establish a proof of concept of the clinical benefit of the mRNA-1608 vaccine candidate. On May 2, 2024, Moderna announced that the Phase 1/2 study of mRNA-1608 was fully enrolled. The actual study Start Date was September 6, 2023; the Last update was  September 24, 2024; and the Estimated Primary Completion Date is April 11, 2025.

As of April 223, 025, the U.S. Food and Drug Administration (FDA), the European Medicines Agency, and the U.K. have not approved a herpes preventive vaccine. An analysis published in December 2024 found the global economic cost of herpes infections to be $35 billion annually. In 2025, people can order a herpes test commercially from laboratories. As of April 2025, clinical trials for herpes are accepting new participants.

Massachusetts-based Moderna, Inc. (NASDAQ: MRNA), a biotechnology company, is pioneering messenger RNA therapeutics and vaccines. Moderna is developing vaccine candidates against latent viruses, including cytomegalovirus, Epstein-Barr virus, Human immunodeficiency virus, herpes simplex virus (HSV), and varicella-zoster virus (VZV).

mRNA-1608 Herpes Vaccine Indication

HSV has developed numerous defense mechanisms to evade innate and adaptive immunity systems. In the U.S., approximately 18.6 million adults ages 18 to 49 live with HSV-2, known as genital herpes. The U.S. CDC categorizes herpes simplex viruses into two types: HSV-1 primarily infects the mouth, face, and genitals, while HSV-2 primarily infects the genitals. Both herpes viruses establish lifelong latent infections within sensory neurons from which they can reactivate and re-infect the skin.

mRNA-1608 Herpes Vaccine Candidate News

December 11, 2024 - An estimated 846 million people aged between 15 and 49 are living with genital herpes infections.

May 4, 2022 - Moderna confirmed that preclinical studies are underway for the mRNA-1608 vaccine candidate.

April 2022 - The NIH published a study discussing the trivalent mRNA-lipid nanoparticle approach for a prophylactic genital herpes vaccine, as well as its ability to induce higher titers of neutralizing antibodies and more durable CD4+ T follicular helper cell and memory B cell responses than protein-adjuvanted vaccines.

March 2022: Moderna Inc. confirmed that preclinical studies are underway for VZV (mRNA-1468) and HSV (mRNA-1608) vaccine candidates. Both are members of the Herpesviridae family, which establishes life-long latent infections.

February 18, 2022 - Moderna, Inc. announced an expansion of its mRNA vaccine pipeline with three new development programs. "We are pleased to announce these new development programs, which reflect the continued productivity of our platform and the potential of our mRNA technology to impact the lives of hundreds of millions of people," said Stéphane Bancel, Chief Executive Officer of Moderna. 

December 22, 2021 - Translational Research published a Review article: An mRNA vaccine to prevent genital herpes. 

July 27, 2020 - PLOS published a study that concluded: We consider the HSV-2 trivalent mRNA vaccine a promising candidate for clinical trials to prevent genital herpes caused by HSV-1 and HSV-2.

mRNA-1608 Herpes Vaccine Candidate Clinical Trials

As of 2025, Moderna publishes clinical trial updates at this web link. According to GlobalData, Phase II drugs for Genital Herpes have a 30% phase transition success rate, indicating a benchmark for progressing into Phase III. 

A Phase 1/2, Randomized, Observer-Blind, Controlled, Dose-Ranging Study of mRNA-1608, an HSV-2 Therapeutic Candidate Vaccine, in Healthy Adults 18 to 55 Years of Age With Recurrent HSV-2 —Last updated September 24, 2024, has a completion date of 2025-04-11. This study aims to generate safety and immunogenicity data and establish a proof-of-concept of the clinical benefit of the mRNA-1608 vaccine candidate.