New Delhi: The dengue vaccine Qdenga, pre-approved by the World Health Organization in May, has shown more than 50 per cent efficacy in reducing the number of cases, with lasting effects and a good safety profile, according to a review of 19 studies. The "first comprehensive global" review, covering more than 20,000 participants, found that upon receiving the two-dose vaccine, over 90 per cent of adults and children elicited an immune response against all four variants (serotypes) of the dengue-causing DENV virus. Of the 19 studies analysed, 13 contained data from Asian and South American locations where the disease is endemic. "Given the results in terms of safety, immunogenicity, and efficacy, the administration of two doses can undoubtedly be a key tool for dengue prevention," said Maria Elena Flacco from the University of Ferrara, Italy, and the lead author of the study published in the journal Vaccines.

What is Qdenga?
Developed by the Japan-based Takeda Pharmaceutical Industries Limited, the Qdenga vaccine - also called TAK-003 - is a live-attenuated vaccine, containing weakened versions of the four serotypes of the DENV virus. "TAK-003 showed an excellent safety profile, and the immunogenicity after two doses against the four DENV serotypes was higher than 90 per cent among both adults and children/adolescents who were either seronegative or seropositive at baseline," the authors wrote. While seropositive indicates a prior dengue infection or exposure to DENV virus, seronegative indicates none of these.

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The authors also found that among those receiving a single vaccine dose, more than 70 per cent of adults and over 90 per cent of children and adolescents developed antibodies against the viral infection. "One of the included studies, with a very large sample, had a relatively long follow-up (4.5 years) and provided robust evidence of the long-term safety (and immunogenicity) of TAK-003," the authors wrote.

Approval for use in India
In February, Takeda and Biological E Limited, Hyderabad, announced a strategic partnership to accelerate access to the Qdenga vaccine. It is not yet approved for use in India. By ramping up its manufacturing capacity to up to 50 million doses a year, Biological E will help accelerate Takeda's efforts to produce 100 million doses a year within the decade, according to the partnership. While the Qdenga vaccine has shown promising results, a comprehensive estimate of its effectiveness and safety was not available, the study's authors said. The dengue-causing DENV virus spreads to humans from the bite of infected female Aedes aegypti mosquitoes (vector). 

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Symptoms of dengue fever
Symptoms of dengue can include high fever, severe headache, muscle and joint pain, and rashes. In severe cases, the disease can be fatal. Tropical and sub-tropical climates are known to favour transmission of the vector-borne disease. About half the world's population is at risk of dengue, cases of which have grown dramatically in recent decades. Yearly cases reported were over five lakh in 2000 and have increased to 52 lakh in 2019, according to the World Health Organization (WHO). Asian countries represent 70 per cent of the affected global population, even as the mosquito-borne disease is now endemic in over 100 countries from across Africa, the Americas and the Western Pacific, according to the UN health agency. With climate change driving warmer temperatures and humidity around the world, the habitat of mosquitoes that carry the DENV virus is also expanding, leading to new dengue outbreaks in more countries, including those in Europe and the eastern Mediterranean. Prevention and control of dengue currently hinges on vector-control measures, and there is no specific treatment for the disease, according to WHO. 

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