Detailed analysis of Sanofi’s dengue vaccine, the first to show efficacy against the fever, has excited observers even if its benefits are more moderate than had been hoped.

The French giant’s Sanofi Pasteur division announced the publication in The Lancet of its first landmark Phase III dengue vaccine efficacy study conducted in five countries in Asia. Results show overall efficacy against symptomatic dengue of 56.5% in children aged two to 14 after a three-dose vaccination schedule and an 88.5% reduction of dengue haemorrhagic fever, the severest form.

The study also showed a clinically important reduction in the risk of hospitalisation due to dengue by 67% during the study. Each year, some 500,000 people, including children, require hospitalisation from dengue, which caused by four virus serotypes and is a threat to nearly half of the world's population; the World Health Organisation estimates up to 100 million infections per year.

The study’s authors wrote that in view of the high disease burden in endemic countries, Sanofi’s dengue vaccine, “despite moderate overall efficacy, could have a substantial effect on public health”. Maria Rosario Capeding from the Research Institute for Tropical Medicine in the Philippines and the study’s principal investigator, noted that the vaccine's impact on preventing dengue haemorrhagic fever is noteworthy, and a treatment “that is able to avoid the personal suffering and reduce this significant health burden would change the lives of millions”.

John Shiver, R&D chief at Sanofi Pasteur, said the results “take us closer to our ambition to bring the first vaccine against dengue to the world”. He added that “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”.

One-dose efficacy as high as after three

In a Lancet comment, Annelies Wilder-Smith from the Nanyang Technological University in Singapore wrote that perhaps the most interesting finding was that efficacy after at least one dose was almost as high as that after three doses. She added that because three doses six months apart “is an inconvenient and costly immunisation schedule for scale-up in national programmes,the question of whether sufficient efficacy can be achieved with a lower number of doses deserves further assessment”.

She went on to say that “this Phase III trial may signify the dawn of a new era in dengue control. But the morning fog has not yet lifted as dengue continues to puzzle because of its complex immunology”.

Prof Wilder-Smith concluded by asking “whether the armamentarium of alternative vaccine candidates presently in the pipeline (including inactivated, live attenuated, chimeric, recombinant, subunit and DNA vaccines) will improve efficacy beyond 56% remains to be established. For the moment, the (Sanofi) vaccine is the best we have; however, with 56% efficacy it will never be a single solution”.

The data will be supplemented by results from a second Phase III study in Latin America and the Caribbean, including more than 20,000 children and adolescents aged nine to 16.