An antibody lowered dengue virus levels in the first trial to treat the infection itself

An experimental monoclonal antibody rapidly reduced dengue virus levels and shortened fever in a phase 2 trial in India, and the authors describe it as the first therapy to show preliminary efficacy against wild-type dengue in humans [s1]. The result is early — a dose-finding study of 250 adults with no serious safety signals but no proof yet that patients end up better off — but it is a genuine first in a disease that has never had a specific treatment [s1] [s2].

Dengue is the world's most widespread mosquito-borne viral infection. About half of the world's population is now at risk, with an estimated 100 to 400 million infections a year, and there is no specific treatment currently — care is limited to fluids, rest and pain relief [s2]. A drug that acts on the virus itself, rather than the mosquito or the immune response, would be a new category of tool.

What the trial did

The study, published in JAMA Network Open, was a phase 2, single-blind, randomised, placebo-controlled trial run at 12 hospitals in India between 19 September 2021 and 13 May 2023 [s1]. It enrolled adults aged 18 to 60 with dengue and fever that had started within the previous 48 hours, excluding those with severe dengue or dangerously low blood counts [s1].

A total of 250 participants were randomly assigned in equal numbers — 50 per group — to a single slow intravenous infusion of the antibody, called Dengue-mAb, at 3, 5, 7 or 9 mg per kilogram, or to placebo [s1]. The median age was 30 years and 180 participants (72.3%) were male [s1]. The antibody is designed to work across all four dengue serotypes, and the trial is registered in India as CTRI/2021/07/035290 [s1].

What happened

The two primary outcomes were the reduction in viraemia at 24 hours and any serious adverse events judged to be caused by the drug [s1]. On safety, there were no causally related serious adverse events [s1].

On the virus, the antibody outperformed placebo. The adjusted mean reduction in viral load at 24 hours rose with dose, from 1.93 log units at 3 mg/kg to 2.35 log units at 9 mg/kg, against 1.29 log units with placebo [s1]. Among the 32 participants who had detectable virus in the blood at the start, those given 5 to 9 mg/kg were clear of dengue virus by 8 hours, compared with 72 hours on placebo [s1].

Fever cleared faster too. Median time to fever clearance was 3.5 hours with the 5 mg/kg dose and 2.0 hours with 7 mg/kg, against 26.8 hours with placebo, with hazard ratios of 2.6 and 2.8 respectively [s1]. By 24 hours, fever had cleared in every patient on the 5 and 7 mg/kg doses — 14 of 14 in each — and in 58.3% of the placebo group [s1].

What it does and does not establish

The authors' conclusion is careful: Dengue-mAb was safe and well tolerated and rapidly reduced viraemia and fever at 5 and 7 mg/kg, making it the first therapeutic against wild-type dengue to show preliminary efficacy in humans [s1]. Every word of that is a laboratory and clinical measure — virus in the blood, temperature — not a patient outcome.

That distinction is the whole story here. Dengue's danger is not the fever but the small fraction of cases that progress to plasma leakage, bleeding and shock, usually after the fever breaks. This trial excluded severe dengue and was not designed or sized to show that faster viral clearance prevents those complications [s1]. Clearing virus sooner is a plausible mechanism for doing so, but plausibility is not evidence, and antibody therapies in flaviviruses carry a specific theoretical worry — antibody-dependent enhancement — that only larger trials with clinical endpoints can rule in or out.

The trial was also modest in size, with roughly 50 patients per arm and small subgroups behind the fever-clearance figures — 14 patients here, 12 there — so the confidence intervals are wide [s1]. Timing is the other constraint: participants had to present within 48 hours of fever onset, and a treatment that only helps in the first two days is a demanding thing to deliver in the settings where dengue is heaviest.

What to watch

The next step is a larger trial powered for clinical outcomes — progression to severe dengue, hospitalisation, safety across serotypes and prior-infection status — before this becomes a treatment anyone can use. Dengue's tool kit has been building on the prevention side, from Wolbachia mosquito programmes to longer-term vaccine data, and small-molecule antivirals such as mosnodenvir are being tested in parallel. An antibody that works on established infection would sit alongside those, not replace them.

This article describes trial results. It is not medical advice, and nothing here should be used to start, stop or change treatment.

Sources

• Safety and Preliminary Efficacy of Dengue Monoclonal Antibody in Adult Patients: A Randomized Clinical Trial, JAMA Network Open, 2026
• Dengue and severe dengue — fact sheet, World Health Organization, 21 August 2025