HSV-2: New Models Could Pave the Way to Better Prevention
"Mathematical modeling offers fresh insights into optimizing vaccine strategies for herpes simplex virus type 2 (HSV-2)."
Herpes simplex virus type 2 (HSV-2) is a common sexually transmitted infection affecting millions worldwide. While there's currently no licensed vaccine, ongoing research explores the potential of vaccination to reduce its spread.
Mathematical models play a vital role in understanding and controlling infectious diseases like HSV-2. These models simulate disease dynamics, helping researchers test different intervention strategies virtually before implementing them in the real world.
Recent research published in the journal Theoretical Biology and Medical Modelling presents a new multi-group SVIRI (Susceptible-Vaccinated-Infective-Recovered-Infective) epidemic model for HSV-2. This model allows researchers to investigate the impact of vaccination, waning immunity, and relapse on the spread of the virus.
An Unmet Need
A vaccine for genital herpes does not currently exist, despite the prevalence of this sexually transmitted disease. The Herpes Simplex Therapeutic Vaccine Tracker 2025 reports that 1 in 6 Americans have genital herpes and describes clinical trials targeting recurrent outbreaks and viral shedding. ClinicalTrials.gov lists mRNA-1608 as a Phase 1/2 therapeutic candidate vaccine being studied in healthy adults ages 18 to 55 with recurrent HSV-2 genital herpes.
Prophylactic and Therapeutic Paths
The vaccine value profile distinguishes prophylactic vaccination, intended to prevent infection among susceptible people, from therapeutic vaccination for people with symptomatic genital HSV-2 infection. A 2024 review states that an effective prophylactic or therapeutic HSV vaccine remained elusive as of 2024. Research also continues to compare vaccine platforms: a 2026 study reported excellent protection after intravaginal vaccination with a replication-competent vaccine, suggesting that the natural route of HSV-2 infection may matter when reducing infection and spread.
What Does the New HSV-2 Model Reveal?
The SVIRI model offers several key advantages over previous models, allowing researchers to:
- Account for vaccination: The model directly incorporates the impact of vaccination programs.
- Consider waning immunity: It acknowledges that vaccine-induced protection may decrease over time.
- Incorporate relapse: The model recognizes that individuals can experience recurrent outbreaks even after periods of remission.
- Structure by risk group: The model can be adapted to analyze various population structures, including risk, sex, and age groups.
Prime, Pull, and mRNA
In a Yale School of Medicine study, mice receiving a “prime and pull” treatment were highly resistant to infection: 80% showed no signs of disease over six months, compared with 40% after intramuscular injection alone. A 2026 Nature study describes an mRNA vaccine investigation for HSV types 1 and 2, while noting that no prophylactic or therapeutic HSV vaccine had been approved to date. Current research therefore includes both localized immune strategies and newer mRNA approaches.
Why Success Has Been Elusive
The Nature review describes herpesviruses as causing a high disease burden while vaccines remain lacking, and concludes that developing efficacious vaccines is challenging. One documented failure involved the glycoprotein D/AS04 vaccine, which failed to prevent HSV-2 in clinical trials. In mice, that failure was reproduced even though the vaccine generated neutralizing antibody, because it did not generate antibody-dependent cell-mediated cytotoxicity.
Prevention Versus Immunotherapy
Population modeling found that a campaign reaching 70% coverage over five years, using a vaccine that reduced HSV-2 acquisition and reactivation susceptibility by 75% for 10 years, could reduce HIV incidence by 30% to 40% after 20 years, with a modeled range of 4% to 66%. A review reports that genital herpes caused by more than one HSV-2 strain is uncommon, occurring in 3% to 7% of cases, and notes that neonatal herpes is a feared consequence of genital herpes. Separately, mRNA-1608 is described as Moderna’s therapeutic candidate for people with recurrent genital HSV-2, functioning as immunotherapy rather than as a preventative vaccine.
Looking Ahead
While mathematical models are simplifications of reality, they provide valuable insights for guiding public health strategies. This new SVIRI model offers a framework for exploring optimal vaccination approaches for HSV-2, ultimately contributing to more effective prevention efforts. More research is needed to confirm the model's predictions and translate these findings into real-world programs.
Smarter Vaccine Design
Expert commentary identifies in silico analysis and bioinformatics as emerging approaches for developing vaccines with enhanced targets and formulations. These methods are not yet fully established for HSV disease. Current studies using them for HSV vaccine design may nevertheless help guide future vaccine strategies.
A Diverse Research Pipeline
A 2026 trials update identifies BioNTech’s HSV-2 vaccine, Moderna’s mRNA-1608, a CRISPR HSV-1 trial, and GSK’s GEN-003 among the efforts being assessed. The source frames these programs around determining which initiatives are active, stalled, or genuinely promising. This pipeline spans vaccines, therapeutic candidates, and gene-editing research rather than a single approach to herpes prevention or cure.
From Biology to Population Impact
Mathematical models have been used to describe HSV-2 transmission dynamics and estimate the population-level effects of preventive and therapeutic vaccination. This modeling work is intended to inform vaccine development, licensure, and implementation. A 2024 review places these efforts within the broader biology of HSV, including lytic and latent infection, reactivation, and virus-host immune interactions.