Key Terms & Concepts — UPSC Mains
Antibody-Dependent Enhancement (ADE)
"An immunological phenomenon in which prior antibodies to one virus serotype help, rather than hinder, a subsequent infection with a different serotype, worsening disease severity."
Antibody-Dependent Enhancement (ADE) occurs when antibodies produced in response to a first infection fail to neutralise a second infection with a related but distinct viral serotype, and instead bind to the new virus in a way that helps it enter host cells more efficiently. Rather than protecting the individual, the residual antibodies from the first exposure make the second infection more severe than it would otherwise have been. ADE is the central design problem in dengue vaccinology and the reason a usable dengue vaccine must be tetravalent, protecting evenly against all four serotypes (DENV-1 to DENV-4) at once. A person's first dengue infection confers durable, lifelong immunity to that specific serotype but only brief, partial cross-protection against the other three. When cross-protection wanes and a different serotype infects the person later, ADE raises the risk that this second infection becomes severe dengue, historically termed Dengue Haemorrhagic Fever or Dengue Shock Syndrome. The phenomenon is not merely theoretical: it drove the 2017 Dengvaxia controversy in the Philippines, where a vaccine given to children who had never previously had dengue was later found to increase their risk of severe disease on natural infection, prompting WHO to restrict the vaccine to people with confirmed prior infection. It resurfaced in 2026 with India's approval of Qdenga (TAK-003), whose trial data showed strong protection in previously infected (seropositive) recipients but a weak or even adverse signal for DENV-3 in children who had never been infected before (seronegative), reviving the debate over mandatory pre-vaccination serostatus screening.
ADE is Mains-testable across GS2 (vaccine regulation and public health ethics) and GS3 (biotechnology and immunology), and is the analytical key to understanding why hyper-endemic co-circulation of multiple dengue serotypes and uneven vaccine efficacy are both dangerous in the same specific way.
- 1 Occurs when non-neutralising antibodies from a first infection help a different serotype infect cells more efficiently on re-exposure
- 2 Central design constraint for dengue vaccines, which must protect evenly against all four serotypes (DENV-1 to DENV-4)
- 3 A person's second dengue infection with a different serotype carries a substantially higher risk of severe dengue than the first
- 4 Drove the 2017 Dengvaxia (Sanofi) controversy in the Philippines and WHO's subsequent restriction to seropositive recipients
- 5 Resurfaced with India's 2026 approval of Qdenga (TAK-003), whose trial showed weak/adverse DENV-3 protection in seronegative children
- 6 Explains why hyper-endemic co-circulation of multiple serotypes in the same season raises population-level severe-dengue risk
- 7 Central to the policy debate on mandatory pre-vaccination serostatus screening versus universal rollout
India's Central Drugs Standard Control Organisation approved Qdenga in July 2026 on the condition of a post-marketing safety study, precisely because ADE makes uneven, serotype-specific vaccine efficacy a potential safety risk rather than just an efficacy shortfall.
