India approves first dengue vaccine Qdenga amid rollout challenges

Dengue fever is a vector-borne viral illness caused by four antigenically distinct serotypes — DENV-1, DENV-2, DENV-3, and DENV-4 — transmitted primarily by the Aedes aegypti mosquito and secondarily by Aedes albopictus. The World Health Organization (WHO) classifies dengue as one of the ten threats to global health, estimating 100–400 million infections annually worldwide. No specific antiviral treatment exists; clinical management remains supportive. A critical immunological feature of dengue is that infection with one serotype confers lifelong immunity only to that serotype, while a subsequent infection by a different serotype can trigger antibody-dependent enhancement (ADE) — a mechanism by which pre-existing antibodies paradoxically amplify viral replication, increasing the risk of severe dengue haemorrhagic fever or dengue shock syndrome.

In India, vector-borne disease control is governed under the National Vector Borne Disease Control Programme (NVBDCP), administered by the Ministry of Health and Family Welfare. India has experienced a sustained rise in reported dengue burden over the past decade, driven partly by genuine disease spread and partly by improved surveillance infrastructure. The Aedes mosquito's breeding range has expanded beyond dense urban cores into semi-urban and rural districts, where drainage infrastructure and vector control capacity are weaker. This epidemiological shift has made the case for a preventive vaccine more urgent.

The first licensed dengue vaccine globally, Dengvaxia (by Sanofi Pasteur), became a cautionary tale when its rollout in the Philippines caused severe adverse outcomes in seronegative children — those without prior dengue exposure — because ADE was triggered by the vaccine itself acting as a 'first infection'. The resulting controversy prompted stricter global regulatory scrutiny and reinforced the principle that dengue vaccination must account for prior serological status.