India’s fight against dengue has a data problem doctors can’t ignore, warns expert

Official surveillance figures routinely paint a deceptive picture, framing dengue as a managed, predictable public health challenge. In reality, experts warn that these reported numbers reflect a mere fraction of the true threat, an incomplete, highly fragmented snapshot of a much larger crisis unfolding across the country.

With The Lancet estimating that India accounts for nearly one-third of the global dengue burden, the actual number of infections could run into tens of millions annually, driven by widespread underreporting and asymptomatic cases.

This is not merely a statistical gap but a growing clinical and policy emergency. Climate change is expanding the habitat of Aedes aegypti mosquitoes into previously cooler regions such as Himachal Pradesh and Ladakh, while shifting dengue serotypes are increasing the risk of severe disease in secondary infections, particularly among young adults. Against this backdrop, the urgency for improved surveillance systems and effective therapeutic and vaccine strategies has never been greater.

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Firstpost talked to Dr. Shikha Taneja Malik, Senior Scientific Affairs Manager, Drugs for Neglected Diseases initiative (South Asia) to the structural blind spots in India's surveillance, the changing biology of the virus and the critical regional race for dedicated therapeutics and vaccines.

India reported 2.89 lakh dengue cases in 2023, but you suggest this is a major undercount. What is the real burden and why are so many cases missed?

Dr. Shikha: The 2.89 lakh figure reflects only what our surveillance system captures, but it is almost certainly a fraction of the true burden. The Lancet estimates India accounts for around 33 per cent of the global dengue burden. Globally, there are an estimated 400 million dengue infections annually, which suggests India’s real burden could be in the tens of millions each year. Some studies indicate actual infections may be 20 to 200 times higher than reported cases.

There are multiple reasons for underreporting. First, many infections are asymptomatic or resemble generic viral fever, so patients either do not seek care or are treated symptomatically without testing. For every confirmed case, there may be several undiagnosed infections.

Second, surveillance is largely passive and depends heavily on public health facilities, while a large share of care occurs in the private sector, which does not consistently report cases.

Third, diagnostic limitations also play a role. Tests such as NS1 antigen detection or PCR are not uniformly available at primary healthcare levels, especially in rural and semi-urban areas. While efforts are underway to expand access to testing, gaps remain.

Finally, there can be systemic disincentives for reporting outbreaks due to administrative or political pressure, which may affect active case detection. Accurate numbers are critical because they determine funding priorities, policy urgency and investment in research and therapeutics. Without reliable data, dengue response remains under-prioritised.

Dengue is often called a monsoon disease. Is that still accurate?

Dr. Shikha: No, that label is now outdated and potentially misleading. It creates a false sense of safety for most of the year, but dengue transmission is increasingly occurring beyond the monsoon months.

What we are seeing across India and across the region is a fundamental shift in the transmission pattern. Dengue used to follow a fairly predictable seasonal curve — cases would spike between July and November, track the monsoon, and then recede. That curve is flattening. We are now seeing cases in February, in March, in May, months that were previously considered safe. Delhi, Mumbai, Bengaluru, cities that used to have clear off-seasons for dengue are reporting year-round transmission.

Between 1951–60 and 2012–21, the number of months suitable for dengue transmission in India grew by 1.69% annually, reaching 5.6 months. Warmer temperatures, altered rainfall patterns, unplanned urbanisation, and poor sanitation have lengthened transmission seasons, making dengue a year-round systemic crisis.

Models now predict year-round transmission in coastal regions, though monsoon months will retain the highest peak.

Are serotype shifts contributing to rising severity, especially among young adults?

Dr. Shikha:

Yes, India is witnessing active serotype shifts and they directly explain rising severity, especially in young adults.

In 2024, in Bengaluru, an analysis of 1,600 samples revealed a striking dominance of DENV-3 at nearly 80%, displacing DENV-4, which had been the predominant serotype in southern India since 2015. In Central India, a novel DENV-2 strain displaced the previously circulating DENV-1, exhibiting higher viral loads and a greater reproduction number, driving rapid disease spread.

Initial infection with one of the four dengue serotypes results in lifelong immunity to that specific serotype. Whereas, a secondary infection with a different serotype can trigger Antibody-Dependent Enhancement (ADE). When pre-existing antibodies from a prior dengue infection fail to neutralize a new, different serotype, they instead enhance the infection, increasing severity. In India, secondary infections with DENV-2 are most often associated with severe disease outcomes.

Young adults who were exposed to one serotype in childhood are now encountering a new dominant serotype, making them especially vulnerable to severe secondary infections.

What would an effective dengue therapeutic change for India and Southeast Asia specifically?

Dr. Shikha: An affordable and effective dengue therapeutic would be a game-changer for a region carrying a disproportionate global burden. The WHO Southeast Asia region alone accounts for more than half the world's dengue burden, with India, Bangladesh, Indonesia, Myanmar, Sri Lanka, and Thailand among the 30 most endemic countries globally. Yet, no safe, effective specific drug currently exists; treatment remains entirely supportive.

India's dengue costs reached US$5.71 billion in 2016, with hospitalization driving the bulk of expenditure. An antiviral that prevents disease progression would directly slash these costs and relieve already overstretched public health systems.

Recognising this urgent treatment gap, efforts to develop affordable and accessible dengue treatments are already underway through the Dengue Alliance - a global partnership founded in 2022 by institutions in India, Brazil, Malaysia, and Thailand, with DNDi as the Secretariat.

With endemic countries at the helm, the Alliance is advancing pre-clinical research, evaluating promising drug candidates, and preparing for clinical trials, while strengthening cross-country collaboration to address knowledge gaps, support future registration pathways, and accelerate access once treatments become available.

Sustained investment from governments and funders will be critical to ensure these efforts translate into timely and equitable access for patients. Preparations are underway for multi-country trial for a potential dengue treatment led by DNDi and dengue alliance members..

Is dengue spreading into regions that were previously unaffected?

Dr. Shikha: Yes. Climate change and urbanisation are expanding the range of Aedes mosquitoes into new geographies. Rising temperatures, changing rainfall patterns, increasing humidity, and rapid unplanned urbanisation are creating more favourable conditions for Aedes aegypti mosquitoes to survive and transmit the virus for longer periods each year. As transmission seasons lengthen, regions once considered climatically unsuitable for dengue are becoming increasingly vulnerable.

Since the mid-1990s, dengue has rapidly spread to regions where it was historically non-existent, including Odisha, Arunachal Pradesh, and Mizoram. In the early 2000s, dengue was endemic only in a few southern and northern states; it has since spread to many states, including union territories.

The shift is particularly visible in hilly and cooler geographies. Himachal Pradesh, for example, recorded a surge from 349 cases in 2021 to 2,563 in 2022, with outbreaks now occurring regularly in sub-Himalayan regions previously considered spared. Similar risk has also been predicted in northeast states and Jammu & Kashmir.

In Uttar Pradesh, 2023 recorded the highest dengue cases in five years, with patients reported not just from urban centres but also from semi-urban and rural locations. (2023, Dengue outbreak of 2023 in the state of Uttar Pradesh, North India: lesson learnt and way forwards)

Climate modelling projects further expansion of Aedes albopictus into upper Himalayan regions including Leh-Ladakh and Arunachal Pradesh by 2050, territories once considered climatically unsuitable for dengue transmission.

These trends indicate that dengue is no longer confined to traditionally endemic regions, making it an increasingly widespread public health challenge across India.

What are the key challenges in developing a dengue vaccine in India?

Dr. Shikha: India has remarkable vaccine manufacturing capacity, but dengue presents a uniquely complex challenge. Vaccines exist but remain limited in scope; the currently available dengue vaccine is recommended only for individuals aged 9 to 45 who have had at least one prior infection, excluding many of those most at risk. While newer vaccines are being developed and rolled out in other regions and show broader applicability, pregnant women, infants, and older adults will remain uncovered.

India is making progress, but significant hurdles remain. ICMR and Panacea Biotec launched India's first Phase 3 trial for an indigenous dengue vaccine, DengiAll, across 19 sites in 18 states, enrolling over 10,335 participants with a two-year follow-up. This is promising, but the road ahead is complex.

The Butantan vaccine recently approved in Brazil, was the candidate that was developed by NIH, USA. The same candidate has been in licensed by 3 companies in India, Panacea, SIIPL, and Indian Immunologicals. They are in different stages of development and out of these three, the ICMR and Panacea candidate is the most advanced.

The recent DCGI approval of Qdenga is encouraging. It signals regulatory readiness but for a truly indigenous product, we need ICMR, DBT, and industry aligned around long-term committed financing. India has the science and the manufacturing muscle. What we now need is the coordinated will to see it through, which we are quite hopeful about.

India has strong manufacturing capacity, but coordinated long-term investment and regulatory alignment are needed to accelerate successful vaccine development.