Researchers expressed surprise over the lower than expected efficacy of the vaccine, but nevertheless hailed the demonstration that a vaccine against dengue fever is possible as a 'breakthrough'.
Dengue fever is a mosquito-borne viral disease for which there is currently no specific treatment or vaccine. Consequently, cases are managed with supportive measures. Approximately half the world's population lives in countries where dengue fever is endemic.
In the phase II study, 4,002 Thai children aged 4 to 11 years were randomised to receive either the experimental dengue vaccine or control (rabies vaccine or placebo) at 0, 6 and 12 months.
Overall vaccine efficacy in the per-protocol analysis (n=3,673) was 30.2%, with statistically significant efficacy reported for dengue virus serotypes (DENV) 1, 3 and 4 after at least one injection (61.2%, 81.9% and 90%, respectively) but not after three injections. However, efficacy against DENV2, which accounted for 59% of episodes, was not shown.
Dengue vaccine was well tolerated, with no reported vaccine-related serious adverse events or other safety signals after two years of active follow-up.
The vaccine, developed by Sanofi Pasteur MSD and known as CYD-TDV, is a recombinant, live attenuated, tetravalent vaccine based on the yellow fever 17D vaccine strain.
Two randomised controlled phase III trials of the vaccine involving more than 30,000 children are currently underway in Asia and Latin America. They are designed to assess its efficacy in preventing symptomatic virologically confirmed dengue cases, regardless of severity or serotype.
The Asian trial is recruiting children aged 2 to 14 years and is expected to complete in July 2014. The Latin American trial has enrolled children aged 9 to 16 years and has an anticipated finish date of August 2016.