Sanofi's $1.5B dengue vaccine shows Phase III promise, but questions linger

Capping a 20-year effort to develop the world's first dengue fever vaccine, Sanofi ($SNY) has come through with positive results from a sweeping Phase III trial, but its candidate is not quite a panacea for the often deadly disease.

Detailed results published in The Lancet showed Sanofi's shot reduced the incidence of dengue by 56.5% in children aged 2 to 14, with an 88.5% reduction in hemorrhagic fever, a severe form of the disease. The vaccine also cut the risk of hospitalization by 67%, a statistically significant mark. The two-year study involved 10,275 children across Asia and dosed each with a three-shot regimen.

Despite the vaccine's broad efficacy, however, a closer look at the data paints a more nuanced picture. Dengue comes in four serotypes, and while Sanofi's treatment did well against variants 1, 3 and 4, it charted just 34.7% efficacy in serotype 2, missing statistical significance in one of Asia's most common forms of the disease. Furthermore, the researchers note, the vaccine's efficacy increased with patient age, with the youngest patients deriving the least benefit.

But, considering half the world's population is at risk of contracting dengue, "this vaccine candidate, despite moderate overall efficacy, could have a substantial effect on public health," the investigators wrote, and Sanofi's treatment proved itself safe in the study.

Now, Sanofi is waiting on the results of another 20,000-patient Phase III study, expected later this year, before filing for regulatory nods around the globe. If approved, Sanofi's treatment would be the only vaccine on the market for a tropical disease that infects up to 100 million people a year, according to the World Health Organization.

The company has spent more than $1.5 billion developing its dengue candidate, and now, with positive late-stage results in hand, Sanofi has glimpsed the finish line, hoping to launch the vaccine next year.

"After more than 20 years of commitment in collaboration with the scientific community, we are on course to make dengue the next vaccine-preventable disease," Sanofi Senior Vice President John Shiver said in a statement. "The public health implications of a future dengue vaccine are significant, and these findings are an important stride towards meeting the WHO's strategic goals of reducing dengue mortality by half and morbidity by at least 25% by 2020."

Analysts expect the shot to bring in about $1.4 billion a year at its peak, and Sanofi has already shelled out nearly $1 billion to set up a plant dedicated to producing the vaccine, allowing it to hit the ground running if and when the product is approved.

All the while, rivals including GlaxoSmithKline ($GSK), Merck ($MRK) and Novartis ($NVS) are hammering away at dengue vaccines of their own, but none has made its way into Phase III.

- read the study
- here's Sanofi's statement