Why India’s deadly dengue crisis is now no longer confined to the monsoons

play Live Sign upShow navigation menu.css-15ru6p1{font-size:inherit;font-weight:normal;}Navigation menuNewsShow more news sectionsAfricaAsiaUS & CanadaLatin AmericaEuropeAsia PacificMiddle EastExplainedOpinionWorld CupVideoMoreShow more sectionsFeaturesEconomySportHuman RightsClimate CrisisInvestigationsInteractivesIn PicturesScience & TechnologyPodcastsTravelplay Live Click here to searchsearchSign upNavigation menucaret-leftTrendingUS-Israel war on IranWorld Cup 2026Tracking Israel's ceasefire violationsRussia-Ukraine warDonald Trumpcaret-rightNews|Climate CrisisWhy India’s deadly dengue crisis is now no longer confined to the monsoonsExperts warn that rising temperatures, erratic rainfall and rapid urbanisation are transforming a seasonal disease into a year-round public health threat. xwhatsapp-strokecopylinkgoogleAdd Al Jazeera on GoogleinfoA New Delhi Municipal Council (NDMC) sanitation worker fumigates a slum area to reduce breeding sites for mosquitoes to prevent dengue and other mosquito-borne tropical diseases, in New Delhi, India, on September 11, 2024 [Rajat Gupta/EPA]By Tauseef Ahmad and Sajid RainaPublished On 11 Jun 202611 Jun 2026Gurugram, India — When Nitin Sharma developed a high fever in May, dengue was the last thing on his mind. The monsoon was still weeks away. Like many Indians, the 32-year-old software engineer from Gurugram, a business district outside New Delhi, had grown up believing dengue was a disease that arrived with the rains and disappeared once the monsoon season ended. So when headaches, severe body aches and fatigue forced him to visit a private hospital in Gurugram, he assumed he was suffering from a routine viral infection. “I thought it would be some seasonal fever,” Sharma said. “Nobody in my family even considered dengue because it wasn’t monsoon season yet.” A blood test revealed otherwise. Doctors diagnosed him with dengue fever. For nearly two weeks, Sharma remained away from work as weakness and fatigue persisted long after the fever subsided. “What shocked me most was the timing,” he said. “Earlier, if someone had a fever in April, dengue would have been the last thing we thought about.” Doctors across India say Sharma’s experience is becoming increasingly common. Hospitals in several states began reporting dengue infections weeks before the monsoon officially reached the southern state of Kerala last week, reflecting what scientists describe as a growing shift in the behaviour of one of the country’s most widespread mosquito-borne diseases. Health experts warn that rising temperatures, erratic rainfall and rapid urbanisation are helping dengue-carrying mosquitoes survive longer and spread farther than before, gradually transforming what was once considered a seasonal disease into a year-round public health threat. “Dengue is no longer restricted to the post-monsoon period,” said Dr Harshdeep Joshi, professor and head of Community Medicine at Maharishi Markandeshwar Medical College and Hospital in Haryana. “We are increasingly seeing cases outside the traditional season. The transmission window appears to be expanding,” he told Al Jazeera. For decades, dengue outbreaks in India followed a relatively predictable cycle. Cases would begin increasing during the monsoon, peak in the weeks after heavy rains and then decline as temperatures cooled. That pattern is becoming less distinct. Even before this year’s monsoon season officially began, hospitals in several cities reported a rise in suspected dengue cases. According to the National Center for Vector Borne Diseases Control (NCVBDC), India reported 6,927 dengue cases by the end of February, 2026. Although this figure covers only the first two months of the year, it indicates unusually early transmission. For comparison, NCVBDC-linked figures cited in a Frontiers in Public Health study show 6,837 cases were recorded during the entire January–May period in 2021, and 10,172 cases during the same period in 2022. This means that the 2026 figure has already exceeded the full January–May total of 2021 within just two months and is rapidly approaching the early-season burden seen in 2022. While not a perfect like-for-like comparison, epidemiologists say the pattern is significant because dengue transmission in India has historically remained low between January and May. In recent years, however, that seasonal gap has narrowed. The southern state of Tamil Nadu accounts for the highest number of infections this year with 2,873 cases, followed by Maharashtra (786), Kerala (670) and Karnataka (560). Southern states consistently report higher early transmission due to warmer climates, longer mosquito breeding windows, and in some cases, more extensive diagnostic reporting systems. Taken together, the data suggest that dengue transmission is beginning earlier and spreading more persistently across the year than in previous cycles. Official data show that dengue cases in India have remained high in recent years, with 289,235 infections and 485 deaths recorded in 2023, the highest annual burden in recent history. In 2024, India reported 233,519 cases and 297 deaths, while 121,824 cases and 131 deaths were recorded in 2025. Public health experts say these fluctuations reflect the cyclical nature of dengue outbreaks, where large epidemic years increase population-level immunity to dominant serotypes, temporarily reducing transmission in subsequent years. However, they caution that this does not contradict the long-term expansion of dengue’s geographic and seasonal range, which continues to widen due to climate variability, urbanisation and changing mosquito ecology. Doctors say surveillance measures that usually begin around the rainy season now need to start much earlier. “We used to prepare mainly during the monsoon months,” said Dr SM Kadri, a public health consultant and former surveillance officer in Haryana. “Now hospitals and health workers have to remain alert almost throughout the year.” “The decline seen in 2025 should not be interpreted as a retreat of the virus. Dengue transmission in India tends to fluctuate sharply year to year due to a combination of population immunity following major outbreak seasons, changes in circulating serotypes, and local environmental conditions that affect mosquito breeding,” said Dr Aubair Hussain, a Srinagar-based physician. He added that after high transmission years, partial immunity in affected populations can temporarily reduce case loads, but this does not interrupt long-term transmission trends. “Rainfall distribution, temperature variations and urban water storage patterns can also disrupt mosquito breeding in certain pockets, which further contributes to these short-term drops,” he said. A study published in Environmental Pollution (Elsevier) in 2026 analysed dengue data from 20 endemic countries between 2020 and 2024 and found a strong association between long-term exposure to fine particulate air pollution and higher dengue mortality. The study focused on PM2.5 — fine particulate matter small enough to penetrate deep into the lungs and enter the bloodstream. It found that countries with higher levels of PM2.5 pollution recorded dengue death rates three to five times higher than countries with cleaner air. For context, the World Health Organization recommends an annual PM2.5 exposure limit of 5 micrograms per cubic metre, far below the levels observed in most high-burden countries included in the study. The researchers also found that air pollution remained an independent predictor of dengue severity even after controlling for income levels, population density, rainfall, temperature and baseline health conditions, suggesting it may worsen disease outcomes through systemic inflammation or immune stress pathways. “Long-term exposure to fine particulate air pollution can weaken immune and vascular systems, and in dengue-endemic regions, this may significantly increase the severity and fatality of infections when combined with climate and socioeconomic stressors,” said Sakirul Khan, lead author of the study on air pollution and dengue mortality. Another study published in Scientific Reports (January 2025) found that dengue transmission in India is strongly influenced by changing climate conditions, particularly temperature, rainfall patterns and humidity. Based on data from Pune (2004–2015), the study showed that temperatures above 27 degrees Celsius (81F), humidity between 60 and 78 percent, and moderate, evenly distributed monsoon rainfall create conditions that favour dengue spread. It also found that extreme rainfall can reduce transmission by flushing mosquito breeding sites. The model projected a significant rise in dengue risk in future decades under climate change scenarios. India, meanwhile, is accelerating efforts to develop preventive tools. Earlier this year, the government approved Takeda’s dengue vaccine, Qdenga. Takeda is a Japanese multinational pharmaceutical company headquartered in Tokyo and one of the world’s leading vaccine developers. It has partnered with Biological E, a Hyderabad-based Indian vaccine manufacturer, for local production. At the same time, the Indian Council of Medical Research (ICMR), the country’s apex biomedical research body, and Panacea Biotec, a New Delhi-based biotechnology firm, completed Phase III clinical trial enrolment for “DengiAll”, India’s first indigenous single-dose dengue vaccine candidate, involving 10,335 volunteers across India. A Phase III clinical trial is a large-scale human study conducted to confirm a vaccine’s effectiveness, monitor side effects and establish safety before regulatory approval. The Serum Institute of India is also conducting Phase III trials for its vaccine candidate, TetraVax-DV. Researchers hope these efforts will lead to an affordable vaccine capable of protecting against all four dengue serotypes — DENV-1, DENV-2, DENV-3 and DENV-4 — which are distinct genetic strains of the virus. All four serotypes co-circulate in India, making multi-strain protection critical to prevent reinfections and severe disease. But experts caution that vaccination alone will not solve the problem. “Even with an effective vaccine, vector control and surveillance will remain critical,” said Dr Gagandeep Kang, former professor at the Christian Medical College in Vellore. Kadri agreed, saying there is “no single solution”. “Vector control, sanitation, disease surveillance, public awareness and stronger healthcare systems all remain essential,” he said. Back in Gurugram, Sharma says his illness has changed how he thinks about dengue. He now keeps mosquito repellents at home throughout the year and regularly checks flower pots, rooftop tanks and water containers for stagnant water, regardless of the season. “It feels like the disease can happen any time now,” he said. 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