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.