India's first dengue vaccine due in 2027, but a past vaccine's shadow looms

Qdenga is a dengue vaccine made by Japanese pharmaceutical company Takeda. It is tetravalent, meaning it is designed to target dengue’s four serotypes, DENV-1 through DENV-4. India’s Central Drugs Standard Control Organisation authorised it in July for people aged four to 60. This makes it the country’s first widely available dengue vaccine.

Takeda plans to launch Qdenga in India with Dr Reddy’s Laboratories. The vaccine uses a weakened DENV-2 backbone and includes genes for surface proteins from the other serotypes. It is not a DENV-2-only vaccine, but clinicians want to know whether protection is balanced across different strains.

The private-market launch is expected in the first half of 2027. Its arrival could offer another defence as dengue becomes a year-round problem in India. However, doctors want more evidence about durability, regional strain differences, protection in previously uninfected people and possible immunity-related risks.

India’s dengue problem is substantial and increasingly persistent. Reported cases rose from 44,585 in 2020 to 193,245 in 2021. In 2024, authorities recorded 233,519 cases and 297 deaths. Through November 2025, reported cases fell to 113,440, with 94 deaths, the lowest totals since 2021. Dengue is now described as a year-round problem rather than only a seasonal one.

Official figures may miss many infections because people do not always seek care or receive laboratory confirmation. One Indian study estimated that actual dengue cases could be 282 times the number reported. This does not mean every year’s true total is exactly 282 times higher, but it shows how incomplete surveillance may be.

The scale strengthens the case for prevention tools such as vaccination. Yet India’s diverse regions and changing serotypes complicate national policy. Qdenga’s value will depend on how well it works across populations, locations and future outbreaks, not only on headline trial results.

Dengvaxia was an earlier dengue vaccine developed by Sanofi Pasteur. After its rollout in the Philippines, further analysis indicated that people who had never previously encountered dengue could face a higher risk of severe dengue and hospitalisation after vaccination, especially during a later infection. The Philippines suspended its programme in 2017, creating major public concern.

The central issue was prior immunity. Dengue has four serotypes, and immunity from one infection does not guarantee protection against the others. In people without previous infection, vaccination could sometimes act like a first exposure, leaving them vulnerable to more serious disease during a later natural infection. This concern is linked to antibody-dependent enhancement, or ADE.

The supplied article does not describe Dengvaxia’s history, but this established experience helps explain current caution. Doctors are asking for clear evidence about Qdenga’s safety and effectiveness in previously infected and uninfected people, across different serotypes and over time.

Qdenga’s pivotal trial results show meaningful, but incomplete, protection. A longer-term analysis reported 61.2% efficacy against virologically confirmed dengue and 84.1% efficacy against dengue-related hospitalisation. These figures describe reductions compared with the relevant comparison group. They do not mean that every vaccinated person avoided infection or that protection was identical for every serotype.

Protection varied according to the dengue serotype involved and whether participants had been exposed to dengue before. The vaccine is tetravalent, but it uses a weakened DENV-2 backbone with inserted genes for other serotypes’ surface proteins. Clinicians therefore want closer examination of serotype-specific results, especially in India’s varied regions.

The reported protection lasted through 4.5 years in the longer-term analysis. Doctors still want to see what happens later, as immunity may decline. The WHO has also flagged uncertainty about DENV-3 and DENV-4 protection in people never previously infected and advises caution in lower-transmission settings.

Qdenga’s arrival could give people and clinicians a new way to reduce dengue’s health burden. Dengue infects millions worldwide, and India now faces outbreaks throughout the year. A vaccine that lowers confirmed infections and hospitalisations could reduce severe illness, pressure on hospitals and disruption for families, even if it cannot stop every case.

The trial’s longer-term results reported 61.2% efficacy against virologically confirmed dengue and 84.1% efficacy against hospitalisation after 4.5 years. Protection differed by serotype and previous exposure. This means vaccination would not remove the need for mosquito control, diagnosis or clinical monitoring. Some vaccinated people could still become infected.

Qdenga is expected to enter India’s private market in the first half of 2027. Its wider effect will depend on affordability, uptake and evidence from India’s diverse regions. Clinicians want more information about durability, circulating strains and safety before supporting broad adoption. WHO guidance also favours strategies suited to local transmission levels.

Antibody-dependent enhancement, or ADE, is an immune phenomenon that can make a later dengue infection more dangerous. Dengue has four serotypes. Infection with one serotype usually creates antibodies that protect well against that same type, but protection against another type may be incomplete. Some antibodies can bind to the new virus without fully neutralising it.

Those attached antibodies may help the virus enter certain immune cells through antibody receptors. The virus can then replicate more efficiently, and the immune response may become more intense. This can raise the risk of severe dengue in some later infections. ADE is one reason clinicians examine whether a vaccine produces strong, balanced protection across serotypes.

The article identifies ADE as a serious concern raised by Dr Sanjeev Bagai, but its supplied text ends before explaining the mechanism in detail. Qdenga’s safety evidence therefore needs careful review by prior infection status, serotype, age and follow-up duration. Waning protection alone does not prove that ADE or harm will occur.

The four dengue serotypes are DENV-1, DENV-2, DENV-3 and DENV-4. They are related forms of the dengue virus, but infection with one does not guarantee protection against the others. This is why a person can contract dengue more than once. A later infection with a different serotype can carry a higher risk of severe disease in some people.

A vaccine must therefore protect broadly rather than work strongly against only one type. Qdenga is tetravalent and contains components for all four serotypes. It is built on a weakened DENV-2 backbone, with genes for the other serotypes’ surface proteins inserted. Doctors are still examining whether this design produces balanced protection.

The question matters especially in India, where several serotypes circulate and dominant strains vary by region and over time. Coinfections and viral genetic changes add complexity. Qdenga’s effectiveness may therefore differ by serotype, location and previous exposure, making local surveillance and long-term follow-up important.