Herpes Vaccine Development Stalls in 2026, But Hope Remains

Despite decades of research and a pressing global need, no preventive or therapeutic vaccine for herpes simplex virus types 1 or 2 (HSV-1 or HSV-2) has received regulatory approval in major markets, including the United States and the European Union.

As of March 21, 2026, HSV remains one of the most prevalent sexually transmitted infections worldwide, affecting hundreds of millions of people and causing recurrent oral and genital lesions. The absence of a vaccine continues to drive demand for improved prevention and management options.

However, U.S. NIH researchers have stated that widespread availability of an effective HSV vaccine is unlikely before the early 2030s.

Recent high-profile failures by pharmaceutical companies have intensified the challenges in this field.

Experts and industry observers note that HSV vaccine candidate development has historically proven exceptionally difficult due to the virus's ability to establish lifelong latency and evade immune responses.

In September 2024, GSK plc announced that its therapeutic candidate, GSK3943104, failed to meet the primary efficacy endpoint in the Phase II portion of the TH HSV REC-003 trial, leading the company to halt further development.

Later, in November 2025, Moderna Inc. discontinued its mRNA-1608 therapeutic HSV-2 vaccine candidate as part of a broader review of its pipeline, despite earlier advancements in Phase I trials.

These exits have left BioNTech SE's BNT163 as the most advanced mRNA-based HSV vaccine in active clinical development among major companies. The Phase 1 trial (BNT163-01/NCT05432583) is ongoing, with recruitment completed and an estimated primary completion date of October 2026. This vaccine candidate encodes three HSV-2 glycoproteins (gC2, gD2, and gE2) designed to block viral entry, spread, and immune evasion.

Interim data presented in early 2026 from the dose-escalation portion of the trial (through Day 28 after the second dose) indicate that BNT163 is well-tolerated, demonstrates an acceptable safety profile, and induces binding antibodies and neutralizing titers against HSV-2 antigens. Researchers have described these results as supportive of continued development.

Several other candidates remain in earlier stages of research.

Gene-editing strategies, such as Shanghai BD Gene's BD111 (a Cas9-based approach in Phase 1/2), and preclinical nanobody or oncolytic herpes virus platforms are being explored, but they do not constitute traditional vaccines.

Gilead Sciences recently licensed Assembly Biosciences' helicase-primase inhibitor, ABI-5366, in late 2025 after Phase 1b data showed a 94% reduction in viral shedding, with Phase 2 studies slated for mid-2026.

Aicuris' pritelivir also met Phase 3 endpoints for lesion healing and is advancing toward U.S. FDA submission.

Interested parties can track the herpes vaccine development pipeline through initiatives such as STI Watch and Herpes Cure Advocacy's pipeline updates.

While 2026 has brought more setbacks than breakthroughs for HSV vaccines, the approved herpes zoster vaccine remains highly effective. The fundamental difference between these herpesviruses is in viral behavior and immune evasion.

Shingrix, the recombinant herpes zoster (VZV) vaccine for preventing shingles caused by varicella-zoster virus reactivation, achieves about 90% efficacy in adults, thanks to its glycoprotein E antigen and the powerful AS01B adjuvant, which strongly enhances both antibody and CD4+ T-cell responses against latent virus in neurons.

VZV latency is more static and responsive to strong adjuvanted vaccines like Shingrix, whereas HSV's sophisticated, complex evasion tactics are not.

Despite the string of setbacks in 2025 and 2026, the HSV vaccine field remains active, with promising candidates such as BioNTech's BNT163 advancing through clinical evaluation.

While an effective preventive or therapeutic HSV vaccine may not arrive in 2026, continued research, advocacy, and incremental progress offer genuine hope for better prevention for the hundreds of millions affected worldwide.