The world’s most advanced vaccine against dengue fever developed by French drug-maker; Sanofi SA has proved to be far less effective than expected, during clinical trials conducted in Thailand.
The result of the trials leaves the future of the product uncertain. The success rate of the vaccine reported was a mere 30.2 percent as against 70 percent anticipated at the start of the trials. The poor performance of the vaccine is attributed to its failure to protect against a particular type of dengue virus which was prevalent in Thailand during the trials.
Dengue or break-bone fever is a mosquito-borne disease which threatens almost three billion people. This disease is caused by four types of viruses. Scott Halsted, senior adviser for the non-profit Dengue Vaccine Initiative said that the results of the trials were shocking. He felt the need for further experimentation to understand what exactly happened.
High hopes were pinned on the vaccine since the virus causing dengue belongs to the same class of viruses causing yellow fever and Japanese encephalitis; both of which have been controlled successfully with effective vaccines. Sanofi had earlier declared that the vaccine was effective against three of the four virus strains.
Despite the setback received for making a mixed dengue vaccine containing four different virus strains, Jean Lang; head of dengue vaccine development at Sanofi stated that phase-IIb of the study involving approximately 4,002 children in Thailand showed that a safe dengue shot was feasible.
It was also felt that protection of the vaccine against three virus strains was encouraging. During trials, the vaccine proved to be 60 percent effective against type-1 virus and 80-90 percent effctive against types-3 and 4 viruses. A single dose of the vaccine proved as effective as three doses.
Confirmation on efficacy of the vaccine will be published after completion of phase-III trials.Final stages of this trial are underway with 31,000 participants from Asia and Latin America. Sanofi is reported to have invested 350 million euros in a new French factory for manufacturing the vaccine on successful completion of the trials.
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