Why Kadayanallur pilot is crucial for India’s dengue vaccine rollout

Dengue remains a major public health challenge in India, with gaps in diagnosis and reporting making the actual disease burden difficult to estimate. With Takeda’s Qdenga vaccine receiving regulatory approval in India and an implementation pilot planned in Tamil Nadu’s Kadayanallur, in Tenkasi district, questions remain about its safety, effectiveness and suitability for wider public vaccination.

Speaking to The Federal, public health specialist and vaccines expert Dr Chandrakant Lahariya discusses the evidence behind Qdenga, the lessons from earlier dengue vaccines, the progress of India’s indigenous vaccine candidate Dengyol, and how the Kadayanallur initiative could help prepare the country for a broader rollout.

Edited excerpts:

Where does dengue stand in India today in terms of cases, deaths and geographical spread? Is India's current dengue surveillance strong enough to measure the impact of a vaccine?

Nearly two decades ago, it was largely associated with major cities and metropolitan areas, but today dengue is spreading into rural areas. The disease surveillance, including dengue surveillance, remains suboptimal in the country despite National Centre for Vector Borne Diseases Control (NCVBDC)’s official figures.

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Official figures recorded around three lakh dengue cases and 500 deaths in 2023. In 2024, the reported numbers were approximately 2.5 lakh to 3 lakh cases and around 300 deaths. By September this year, approximately 1.2 lakh cases and 130 deaths had been reported.

These figures do not reflect the actual disease burden, but they provide an indication of its scale, as underdiagnosis and underreporting remain significant challenges.

India has been working to improve disease surveillance through initiatives such as the Integrated Disease Surveillance Programme and laboratory networks. However, many people seek treatment in the private sector, where reporting remains relatively poor. Surveillance in rural areas is also inadequate.

The introduction of a dengue vaccine presents a valuable opportunity for India to strengthen its dengue surveillance system.

How important is the Kadayanallur pilot programme and what results is it expected to generate?

India's drug regulator, the Central Drugs Standard Control Organisation (CDSCO), has granted marketing authorisation for Qdenga, the dengue vaccine developed by Takeda. The vaccine can now be considered for introduction in the country, subject to the relevant implementation decisions.

However, before a vaccine is introduced more widely, it is important to understand the practical challenges involved in delivering it on the ground.

Such initiatives help assess operational feasibility, identify challenges and understand public responses to vaccination.

They also provide an opportunity to identify communication gaps and determine the training requirements of healthcare workers. The clinical trials required before regulatory approval would already have been conducted globally. Qdenga has received regulatory approval in more than 35 countries, and India's regulator has also approved it.

The immediate requirement is to understand how the vaccine can be delivered effectively through the public health system.

The initiative should also provide early indications of adverse events and how effectively they are managed.

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The findings from Kadayanallur could offer useful guidance when Tamil Nadu and other Indian states consider introducing the dengue vaccine.

What does the available evidence say about Qdenga's safety and effectiveness? Which concerns are legitimate, and how does the vaccine work against the different dengue serotypes?

Qdenga, also known as TAK-003, is a live-attenuated, tetravalent dengue vaccine. This means it contains weakened dengue viruses designed to stimulate an immune response without causing the disease in the way a natural infection would.

The vaccine targets all four dengue virus serotypes: DENV-1, DENV-2, DENV-3 and DENV-4. Following clinical trials, the recommended schedule consists of two subcutaneous injections administered three months apart.

In July, India's CDSCO approved Qdenga for individuals aged four to 60 years. However, regulatory approval does not automatically mean that a vaccine should be included in the national immunisation programme. The decision to introduce it into a public health programme requires a separate assessment of operational feasibility and public health priorities.

The Phase III clinical trials of Qdenga were conducted across countries in Asia and Latin America, enrolling approximately 20,000 children and adolescents. The vaccine demonstrated an efficacy of 80.2 per cent against laboratory-confirmed symptomatic dengue. It also reduced hospitalisation by approximately 90 per cent among vaccinated participants compared with those who were not vaccinated.

Follow-up data extending to four and a half years after the second dose showed that the vaccine retained an efficacy of 61.2 per cent against symptomatic dengue and 84 per cent against dengue-related hospitalisation.

These results indicate that Qdenga can provide meaningful protection against dengue. However, its safety profile must continue to be monitored, particularly as vaccination expands to larger populations.

What are the possible side effects of Qdenga?

So far, Qdenga has shown a favourable safety profile. However, some minor adverse events can occur, including pain at the injection site, headaches, muscle aches, fatigue and temporary fever.

One rare but serious adverse event is anaphylaxis, a potentially life-threatening allergic reaction that requires immediate medical attention.

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Brazil's post-marketing surveillance found that approximately 1.4 million doses of Qdenga had been administered, with 43 reported cases of anaphylaxis. This translates to around 3.3 cases per 100,000 doses. None of those reported cases was fatal.

This experience indicates that, with effective emergency response systems and adequate preparedness, such reactions can be managed. Although anaphylaxis is potentially life-threatening, timely recognition and appropriate treatment are essential.

Another concern with dengue vaccines is the possibility of vaccine-associated enhanced dengue. This refers to the potential for a subsequent natural dengue infection to become more severe in some vaccinated individuals. This concern emerged with earlier dengue vaccines, and it remains important to monitor for such outcomes with Qdenga.

What lessons should India draw from countries such as Brazil, where Qdenga has already been introduced?

When India plans a dengue vaccination programme, it can draw on lessons from previous immunisation initiatives, while also learning from the experiences of Brazil and other countries where Qdenga is being used.

The process should be guided by experts and public health specialists to ensure that implementation decisions are based on evidence.

It is important to consider not only the vaccine's clinical efficacy but also the practical requirements of delivering it to eligible populations, maintaining the cold chain, training healthcare workers and communicating effectively with the public.

These considerations will determine how successfully the vaccine can be integrated into India's existing public health infrastructure.

How is Qdenga different from Dengvaxia and what should India watch for?

Dengvaxia was not licensed in India, although it was approved in other countries. It demonstrated efficacy against all four dengue serotypes, but a major safety concern emerged involving what is known as antibody-dependent enhancement.

One key difference between the two vaccines is their underlying viral backbone. Dengvaxia was developed using a yellow fever virus backbone, whereas Qdenga uses a dengue virus serotype 2 backbone.

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Qdenga has demonstrated protection against symptomatic dengue in clinical trial populations that included both people who had previously been infected with dengue and those who had not.

So far, the antibody-dependent enhancement concern associated with Dengvaxia has not been established with Qdenga.

As Qdenga is introduced into new populations, Indian health authorities must maintain strong surveillance to identify any unexpected safety signals, including severe dengue following vaccination and subsequent natural infection.

How close is India’s indigenous vaccine DengiAll to roll out?

India is making encouraging progress with its indigenous dengue vaccine candidate, DengiAll, being developed by Panacea Biotec in collaboration with the Indian Council of Medical Research (ICMR).

The vaccine is undergoing Phase III clinical trials. Like Qdenga, DengiAll is a live-attenuated, tetravalent dengue vaccine. It uses dengue virus strains originally licensed from the US National Institutes of Health.

One potentially important difference is the dosing schedule. Qdenga requires two doses administered three months apart, whereas DengiAll is being developed as a single-dose vaccine. If the single-dose vaccine proves safe and effective, it could offer considerable logistical advantages.

Panacea Biotec announced in January 2026 that enrolment had been completed. Participants are to be followed for two years after receiving the vaccine or placebo to evaluate efficacy, safety and immunogenicity.

An indigenous vaccine could potentially improve the availability of doses and offer advantages in affordability.