India’s dengue burden grows more complex as multiple virus strains circulate together, study finds

India may be entering a more perilous phase in its dengue epidemic, with multiple strains of the virus now circulating simultaneously across much of the country, raising concerns over an increased risk of severe disease, and posing fresh challenges for the rollout of future dengue vaccination programmes.

A two-year nationwide surveillance study by the Indian Council of Medical Research’s (ICMR) Virus Research and Diagnostic Laboratory (VRDL) network found that all four dengue virus serotypes are circulating together in several parts of the country, with nearly one in 14 patients infected with more than one serotype at the same time.

The study, titled ‘Pan-India Molecular Surveillance of Dengue Serotypes, 2023–2025’, analysed 6,889 laboratory-confirmed dengue samples from 45 laboratories across 25 States and Union Territories and found that DENV-2 remained the predominant serotype, accounting for over half of all infections. However, researchers said the broader concern was the widespread co-circulation of multiple serotypes, indicating dengue hyper-endemicity.

Eight States and Union Territories reported the presence of all four serotypes, while 15 reported three circulating simultaneously. Around 7% of patients were infected with two or more dengue serotypes concurrently.

The study also found that patients with concurrent infections were more likely to develop severe manifestations of dengue, including dangerously low platelet counts, bleeding complications and severe joint pain, compared with those infected with a single serotype. While the findings need confirmation through long-term clinical studies, they suggest that simultaneous infection with multiple strains could worsen disease severity.

There are four dengue serotypes (DENV-1 to 4) and severity depends more on secondary infection than serotype, although DENV-2 has often been linked to severe outbreaks. 

The emergence of hyperendemic transmission has implications beyond clinical care, the report notes. India currently has no dengue vaccine in its Universal Immunisation Programme, although indigenous vaccine candidates are in advanced stages of clinical development, and an internationally approved vaccine recently received regulatory clearance for import and sale in India.

Continuous surveillance of circulating serotypes would be critical because vaccine effectiveness varies against different dengue strains, and shifts in the dominant serotype could influence both outbreak intensity and vaccine performance, researchers said.

“Apart from routine steps taken to prevent mosquito breeding, there is certainly a need to incorporate the dengue vaccine into public health programmes, initially targeting endemic areas,” Gautam Menon, Professor of Physics and Biology, Ashoka University, said, speaking about the need for continuous surveillance. “But we also need more regular studies that can alert us about the magnitude of the problem, identify hotspots, and provide early warnings on how serotypes are shifting. This should be an ongoing, regularly reported study,” he added.