Breakthrough for dengue vaccine development

By Helen Albert, Senior medwireNews Reporter

A live-attenuated vaccine against the four strains of dengue virus known as CYD-TDV has demonstrated promising efficacy in a phase IIb trial.

When tested in a group of 4002 Thai school children aged 4 to 11 years, the vaccine was 60-90% effective against strains 1, 3, and 4 of the virus, with only strain 2 showing resistance to the vaccine.

"While there is still much work to be done, these clinical trials mark a decisive step forward in the development of a safe and effective vaccine," said Luiz da Silva, from the Dengue Vaccine Initiative and International Vaccine Institute in Seoul, Korea, who did not take part in the research, in a press statement.

The children taking part in the observer-masked, randomized controlled trial were randomly assigned (2:1) to receive three injections of dengue (n=2669) or control (rabies vaccine or placebo; n=1333) vaccine at 0, 6, and 12 months.

The participants were followed up from baseline until month 25 for dengue infection, which is endemic in Thailand.

Out of 3673 children who completed follow up (2669 dengue vaccine treated and 1333 controls), 134 became infected with dengue during the 25-month period. The efficacy of the vaccine against all four strains was 30.2% overall and 34.9% after at least one injection (intention-to-treat analysis).

However, the low overall efficacy could largely be accounted for by the resistance of strain 2 to the vaccine, as it had an efficacy of 61.2%, 81.9%, and 90.0% against strains 1, 3, and 4 after at least one injection.

No significant adverse effects associated with the vaccine were observed and it seemed to be well-tolerated overall.

As no vaccine currently exists to treat dengue virus infection, these findings are significant, say the authors.

"Our study constitutes the first ever demonstration that a safe and effective dengue vaccine is possible," commented lead author Derek Wallace (Sanofi Pasteur, Singapore) in a press statement.

"Further trials of CYD-TDV are currently underway in a number of different countries, and our hope is that the positive results of this trial will be confirmed by these larger studies, taking place in a wide range of epidemiological settings."

He concluded: "Nearly half a million people are thought to be hospitalized with dengue every year, the majority of which are children, so the development of a safe and effective vaccine has the potential to make a hugely positive impact."

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