India’s first dengue vaccine arrives with a crucial safety caveat, Pg2

Key Highlights:

• India's drug regulator has approved Qdenga, the country's first dengue vaccine, developed by Japanese pharmaceutical company Takeda.
• The vaccine is designed to protect against all four serotypes of the dengue virus (DENV-1 to DENV-4) and is approved for individuals aged 4-60 years.
• A crucial safety caveat exists for seronegative individuals, particularly children, who showed a 25% higher likelihood of DENV-3 infection after vaccination in clinical trials.
• The efficacy of Qdenga against DENV-4 is largely unknown due to insufficient data from trials.
• Researchers recommend pre-vaccination screening for prior dengue exposure, especially for seronegative recipients, to mitigate potential risks.

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Detailed Insights:

• Qdenga has already received approval in over 40 countries globally before its introduction in India.
• The vaccine's efficacy was assessed in a large phase-3 trial involving approximately 20,000 children across dengue-endemic regions.
• Overall efficacy was reported at about 80%, with 82% in seropositive and 75% in seronegative groups.
• The concern arises from "variable vaccine efficacy" across serotypes, specifically a potential enhancement of DENV-3 infection in seronegative vaccinated children.
• This enhanced risk is linked to Antibody-Dependent Enhancement (ADE), where antibodies from a primary infection can worsen a subsequent infection by a different serotype.
• A safe and effective dengue vaccine must be tetravalent, targeting all four serotypes equally to prevent ADE.
• The potential for ADE in seronegative children vaccinated with Qdenga could lead to more severe dengue if they contract DENV-3.
• Given India's large population of seronegative children, ignoring this safety signal could have significant public health implications.

Scientific/Technical Concepts Involved:

• Antibody-Dependent Enhancement (ADE): A phenomenon where antibodies from a previous infection can worsen a subsequent infection by a different viral strain.
• Seropositive: An individual who has previously been exposed to a specific pathogen and carries antibodies against it.
• Seronegative: An individual who has not been exposed to a specific pathogen and lacks antibodies against it.
• Tetravalent vaccine: A vaccine designed to provide immunity against four different strains or serotypes of a pathogen.