Asia’s
first dengue vaccine has been distributed in a mass school-based immunization
program in the Philippines. So far, the program appears to be running without
difficulties, but some health professionals are concerned that the vaccine was
released before researchers could ensure its long-term safety.
From the
beginning, the vaccine’s French manufacturer Sanofi Pasteur has been concerned
about a potential problem with the vaccine — that while it could help prevent
dengue initially, it could later increase the severity of the disease,
according to Dr. Antonio Dans, a professor at the University of the Philippines
College of Medicine.
“The real
dengue we are afraid of is severe dengue, not the mild ones,” Dans said in a
statement. “If a vaccine prevents mild disease but causes severe dengue, we
shouldn’t be using it at all.”
This
possibility is being monitored by the vaccine’s developer, Dans said in a news
release; and since the phenomenon may happen a full three years after
immunization occurs, it will take some time to study the vaccine’s long term
effects.
However,
as the virus infects as many as 400 million people annually, the vaccine for
dengue has been awaited with increasing impatience. In an effort to stem the
spread of the virus in regions heavily burdened by the disease, the WHO
recommended that the drug be introduced in dengue-endemic sites while awaiting
prequalification. According to the organization, the WHO is now waiting on an
application from the vaccine’s manufacturer.
This
raised additional concern from some medical professionals, according to
Philippine media network GMA, who say the immunization program should not have
preceded the prequalification process, especially considering such limited
knowledge of the vaccine’s long-term side effects.
The
vaccine, Dengvaxia, has also been registered in Mexico, Brazil and El Salvador.
Now, the Philippines — which in 2015 saw an almost 60 percent increase in
dengue cases from the year prior — has become the first to make the vaccine
commercially available.
The
company said the Dengvaxia vaccine, which took 20 years and $1.8 billion to
develop, should prevent 80 percent of dengue-related hospitalizations and up to
93 percent of cases of severe hemorrhagic dengue fever. The vaccine is designed
for people ages 9 to 45, and is administered in three separate doses over a
six-month period.
Since the
start of the immunization program last month, Dengvaxia has been administered
to more than 200,000 grade-school students in the capital city of Manila. Of
17,000 people who were injected with the vaccine in the Philippines in February
as part of the clinical study, just 27 developed side effects, Health
Undersecretary Vicente Belizario told reporters.
According
to Health Minister Janette Garin, the $103 million program aims to administer
the first dose of the vaccine to 1 million children by June.
The
history of developing a vaccine for dengue has been wrought with challenges. An
effective vaccine must protect against four closely related viruses that can cause
the disease, and researchers have had limited understanding of how the virus
affects the immune system. Among other barriers making vaccine development more
difficult, there are no easily measurable sign (such as antibodies) that a
person is immune to the disease.
The WHO
estimates that dengue fever, the world’s most common mosquito-borne virus,
infects an estimated 390 million people around the world each year. So far this
year, more than 33,000 dengue cases have been recorded in the Philippines alone.
Lisa
Nikolau
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