GSK recently announced the discontinuation of its herpes simplex virus (HSV) therapeutic vaccine candidate, GSK3943104, following the failure of a Phase I/II clinical trial to meet its primary efficacy goals.
The vaccine aimed to reduce lesions in patients with recurrent genital herpes – a high unmet medical need. Although deemed safe, its lack of efficacy led to GSK’s decision not to advance the vaccine into Phase III trials. This effectively ends GSK’s ambition to bring the first HSV vaccine to market, highlighting the significant challenges inherent in developing a vaccine against genital herpes.
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HSV remains a highly prevalent infection worldwide, with millions affected by either HSV-1 or HSV-2. HSV-1 typically causes oral cold sores, while HSV-2 is the predominant cause of genital herpes, a sexually transmitted infection. According to GlobalData, in 2024 there are an estimated 52 million cases of HSV-2 and an additional 13 million cases of combined HSV-1 and HSV-2 infections across the 16 major markets (16MM: Australia, Brazil, Canada, China, France, Germany, India, Italy, Japan, Mexico, Russia, South Africa, South Korea, Spain, the UK and the US). Projections indicate that these numbers will continue to rise, further emphasising the urgency for effective therapeutic and prophylactic solutions. HSV-2 and combined HSV-1 and 2 cases in the 16MM are projected to reach 54 million and 14 million cases respectively by 2029.
Dormant vaccines pose challenges for therapeutic development
Herpes symptoms can include blisters, fever, swollen lymph nodes and body aches. People infected usually have repeated outbreaks, known as recurrences, with recurrences being less severe than the initial outbreak. While the condition is not curable, antivirals can be used to reduce symptoms.
GSK3943104 was being investigated as a therapeutic vaccine, meaning that it was designed to induce antiviral immunity in individuals who had already contracted the virus, aiming to limit disease progression and reduce outbreaks. This contrasts with prophylactic vaccines, intended to prevent infection from taking hold in the first place. The failure of GSK’s vaccine highlights the inherent difficulties in developing a therapeutic vaccine against a virus that can remain dormant and then reactivate periodically. However, GSK’s trial remains ongoing for routine safety monitoring and to generate follow-up data that could provide valuable information on this infection and inform future research efforts.
While GSK’s departure marks a setback, the focus now turns to companies such as Moderna and BioNTech, both of which are actively developing mRNA HSV vaccines. Moderna’s therapeutic candidate mRNA-1608 is currently in Phase II development, while BioNTech’s prophylactic candidate, BNT-163, is in Phase I development. The innovative use of mRNA technology, which gained global prominence during the Covid-19 pandemic, offers new hope for creating vaccines that could either prevent or mitigate the effects of HSV infections. These companies are now seen as the leading contenders in the effort to address this long-standing health issue.
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