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An
experimental vaccine against dengue -- the mosquito-borne
virus behind a very painful illness -- was found effective
in a new study. In the small trial involving just 41 healthy
volunteers, one dose of the "TV003" vaccine offered 100
percent protection against a particularly tricky strain of
the disease that scientists initially thought might be
outwitting the vaccine. Coupled with earlier indications
that the vaccine also offers strong protection against three
other strains of dengue, the results bode well for ongoing
efforts to control the most widespread mosquito-transmitted
virus in the world, the researchers said. "Development of
vaccines for dengue has been complicated, since disease can
be caused by any of four dengue virus serotypes [strains],"
author explained. And a truly effective vaccine must provide
"equal protection against all four," she added. That's
because if someone who has been sick with one strain of
dengue gets infected with a different strain, the second
strain will cause more serious illness, she explained. Study
author described the current findings as "encouraging,"
though she stressed that more research, on a larger scale,
will be needed to confirm the vaccine's promise. The study
was published online March 16 in the journal Science
Translational Medicine. Dengue strikes roughly 390 million
people each year, primarily in tropical and sub-tropical
environments, according to the study authors. Most
infections are actually mild or without symptoms, the
researchers noted. But upwards of 2 million of those
infected end up with dengue hemorrhagic fever, the study
authors said. Symptoms include a very high fever, severe
headaches, muscle and joint pain, blood vessel leakage and
circulatory failure, according to the U.S. Centers for
Disease Control and Prevention. For roughly 25,000 patients
a year, the disease is fatal. The new vaccine covers all
four strains of dengue. It was first tried out in early
2016, with availability confined to just three countries:
Mexico, the Philippines and Brazil, according to the study
authors. Early tests suggested the vaccine triggered a
robust immune response for three of the strains. But, it
first looked as if the vaccine might be less effective at
producing antibodies for the "dengue 2" strain. Research
team decided to retest the vaccine, focusing not only immune
responses but also on infection rates. The researchers
recruited 41 healthy American adults (average age of about
30). The researchers tested the vaccine on people in the
United States because dengue doesn't often occur in the
United States, which means study volunteers wouldn't have
been infected with any of the strains in the past. Just over
half the group was vaccinated with a single dose of TV003,
while the remainder was given a placebo vaccine. A half-year
later, all were exposed to a genetically modified version of
the dengue 2 strain, the study said. The test strain was
fashioned to prompt what study author described as only a
"minimal health risk," meaning mild and almost symptomless
infections. None of the vaccinated patients developed rashes
or reduced white blood cell counts, or showed any signs of
virus in their blood, the study showed. By contrast, all of
those given a placebo vaccine had the dengue 2 virus in
their blood. Four out of five developed mild rashes, and one
in five saw their white blood cell count drop, the
researchers found. They now plan to study the vaccine in
countries where dengue is widespread. The current findings
are raising hopes not only in the battle against dengue, but
also for efforts to get ahead of other major health concerns
such as the Zika virus. "The dengue virus is closely related
to Zika virus," study author noted. "The team working on
this dengue vaccine is now leveraging their experience in
efforts to develop a Zika vaccine." |