SynAct Pharma has received useful external validation for lead asset resomelagon’s dengue programme, with a World Health Organization (WHO)-led review published in The Lancet Microbe identifying it as one of only six candidates with sufficient efficacy evidence to support further clinical development. Notably, resomelagon is the only host-directed therapy among the six. This is relevant given the substantial unmet need: there are currently no approved dengue-specific treatments, with clinical management largely limited to supportive care. The WHO estimates 100–400m dengue infections annually, while reported cases reached a record 14m+ in 2024. Brazil is a particularly important market given its high disease burden.
Resomelagon is currently being evaluated in the investigator-led Phase II RESOVIR-2 study in Brazil in patients with acute symptomatic dengue. The study compares once-daily oral resomelagon with placebo on top of standard symptomatic care, with reduction in time to disease resolution as the primary endpoint. Additional endpoints assess its potential to reduce dengue warning signs and/or progression to severe disease. This profile aligns closely with the WHO’s preferred characteristics for treatments targeting non-severe dengue, which include oral administration, a favourable safety profile, reduction in symptom burden and prevention of progression to severe disease. Following lower-than-expected dengue incidence during the 2026 Brazilian season, which affected recruitment, SynAct plans to analyse the completed initial portion of RESOVIR-2 separately, with Part 2 enrolment targeted for the H127 dengue season. Part 1 results remain expected in H226, subject to regulatory feedback.
Commercial optionality has also improved through the proposed Hipolabor partnership in Brazil (term sheet signed with a definitive agreement targeted in the coming months). Under the August term sheet, development costs and Brazilian profits would be shared 50:50, with additional milestone payments linked to the first US$200m of cumulative net sales. Hipolabor would bring local regulatory, supply and distribution capabilities, while SynAct importantly retains control of resomelagon outside the arrangement.
We view the WHO recognition as incrementally positive, strengthening the programme’s scientific credibility and potentially supporting further partnering interest. However, meaningful clinical de-risking remains contingent on demonstrating efficacy in RESOVIR-2.