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Dengue Vaccine May Be In Sight

A new study published in The Lancet on Tuesday shows that an effective and safe vaccine for dengue may be in sight.

According to the World Health Organization (WHO), half of the world's population is at risk of dengue, a widespread virus disease carried by mosquitoes.

The virus usually produces flu-like symptoms, but it can also cause a more serious form known as severe dengue, which is a big killer and cause of severe illness in children in parts of Asia and Latin America. Most of the half million people hospitalized with the disease every year are children.

The number of people infected with dengue has risen sharply since 1970, when only 9 countries had severe epidemics. Today, it is thought to be endemic in around 100 countries worldwide.

There is no vaccine against dengue at present, and efforts to produce one are not helped by the fact the disease is caused by four different but related viruses known as DENV 1, 2, 3 and 4. Another difficulty is the disease appears only to affect humans, so animal studies would not be a useful way to test potential vaccines.

Despite this, there are several candidate vaccines for dengue under development.

This week's Lancet study is the first to report a safe and effective dengue vaccine may be possible. The Study The Phase 2b clinical trial tested CYD-TDV, an experimental vaccine from Sanofi Pasteur, who also funded the research. The trial tested the vaccine in 4,002 schoolchildren aged 4 to 11 in Thailand.

The researchers chose Thailand because dengue is endemic there, and many Thais are familiar with the disease and its symptoms.

French and Thai researchers randomly assigned the children to two groups: one received the vaccine and the other received a placebo. There were twice as many in the vaccine group as in the placebo group.

On initial analysis, the results showed while there were proportionally fewer cases of dengue in the vaccine group compared with the placebo (control) group, they were not statistically significant (76 cases/2.8% in the vaccine group, 58/4.4% in the control group).

But further analysis showed the vaccine protected well against DENV 1, 3 and 4 (ranging from 60 to 90%), and it was only DENV 2 that appeared to resist vaccination.

Also, the vaccine appeared to be safe, with no serious side effects reported in the vaccine group.

The researchers note that although the trial only took place in one region, the results are a major step forward in the search for an effective vaccine against dengue.

Co-author Derek Wallace of Sanofi Pasteur, told the press:

"Our study constitutes the first ever demonstration that a safe and effective dengue vaccine is possible." What Next? Wallace said the vaccine is already being tested in larger trials taking place in several other countries. He and his colleagues hope those trials will confirm these early results.

In an accompanying Comment article in the same issue of the journal, Scott Halstead, of the International Vaccine Institute in Seoul, notes:

"Results from this vaccine trial provide hard evidence of protection against DENV 1, 3 and 4 mild disease but insufficient data to calculate vaccine efficacy rates for severe disease."

"Future dengue vaccine trials should provide robust evidence of efficacy against severe disease by selecting populations weighted to assure inclusion of sufficient numbers of at risk children," he adds.

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