A Sanofi vaccine for dengue fever produced disappointing results in a Phase IIb clinical trial, with one of four variations of the virus – serotype 2 or DENV2 -- yielding essentially identical incidence of the disease in partially or fully vaccinated children as did controls.
“This lack of efficacy against DENV2, and the fact that DENV2 was the prevalent serotype during the study, diminished the overall vaccine efficacy in this setting,” an international research team wrote in its study, published in The Lancet, adding that the overall efficacy rate of 30.2% “comes as a complete surprise.”
However, efficacy for the first, third, and fourth dengue fever variations were in a range consistent with a predicted 70% threshol, with the third and fourth variations yielding overall efficacy rates of between 80% and 90% after just one or more doses. As a result, reason for hope remains that a safe and effective vaccine for the tropical disease is yet possible, researchers contended in their study, published in The Lancet.
The team cautioned that the findings for DENV1, 3, and 4 were significant after at least one vaccination, but not after the third “possibly because of the lower number of cases.”
“Although the assumed high efficacy against all four serotypes of dengue virus was not shown, our study constitutes the first-ever demonstration that a safe dengue vaccine is possible,” the team concluded. “In the context of WHO goals to reduce dengue mortality by at least 50% and the morbidity rate by at least 25% by 2020, this study represents a major milestone.”
The research team, led by Prof. Arunee Sabchareon, MD, of Mahidol University in Bangkok, Thailand – which conducted the trial with Sanofi – examined the efficacy of CYD-TDV, a recombinant, live, attenuated, tetravalent dengue vaccine based on the yellow fever 17D vaccine strain and produced in Vero cells. The team randomly assigned some 4,000 healthy Thai schoolchildren between the ages of 4 and 11 years to receive three injections of dengue vaccine or control (rabies vaccine or placebo) at months 0, 6, and 12.