The most detailed global mapping to date of chikungunya has revealed that India may face the highest long-term impact from the mosquito-borne virus. Researchers estimate that millions of people worldwide remain at risk every year. India is predicted to shoulder a particularly heavy share of the burden.
The analysis was conducted by researchers from the London School of Hygiene & Tropical Medicine (LSHTM), Nagasaki University, and the International Vaccine Institute in Seoul. It combines machine learning with epidemiological data. It maps current transmission and also highlights regions that could become vulnerable to outbreaks in the future. These insights offer new strategies for public health planning and vaccine development.
Millions of people remain at risk annually
Based on existing evidence of transmission, the study estimates that 14.4 million people are at risk of chikungunya infections globally each year. Of these, approximately 5.1 million are in India. When researchers accounted for possible spread to new regions not yet considered at-risk, the number rose dramatically to 34.9 million globally, with 12.1 million in India.
Brazil and Indonesia, alongside India, emerged as the countries most likely to experience substantial long-term effects. India and Brazil are expected to account for a significant portion of the global impact of chikungunya. This impact affects both individuals and healthcare systems.
Chronic disability poses biggest challenge
While chikungunya often causes acute symptoms such as high fever and severe joint pain, the long-term impacts are more concerning. The analysis suggests that around 50% of those infected may develop chronic disability. Lingering joint pain can last months or even years after the initial illness.
Researchers found that chronic illness accounted for more than half of the projected disease burden globally. Adults aged between 40 and 60 years were identified as most at risk of long-term effects. Children under 10 and adults over 80 faced the greatest risk of acute illness.
A growing global health concern
Since its re-emergence in 2004, chikungunya outbreaks have been reported in over 114 countries. The virus is transmitted by Aedes aegypti and Aedes albopictus mosquitoes, commonly known as yellow fever and tiger mosquitoes. These vectors also spread other diseases such as dengue and Zika.
Although most patients recover from the initial infection within weeks, more than half continue to experience painful long-term consequences. There are currently no specific antiviral therapies, and treatment relies on supportive care. While two vaccines — Ixchiq® and Vimkunya® — have been approved in some countries, they are not yet widely available.
Using machine learning to predict outbreaks
This study marks the first attempt to use machine learning models to forecast chikungunya’s global burden. Researchers combined infection data with factors such as mosquito distribution, climate suitability, annual rainfall, and national GDP levels.
The model predicted how many people at risk might become infected each year, a measure known as the “force of infection.” On average, between 1.2% and 1.3% of at-risk populations could expect infection annually, lower than dengue’s 6% rate. However, some countries, including Gabon in Africa, could see infection levels of up to 11% among at-risk populations.
Experts stress need for urgent prevention
Lead author Hyolim Kang, a Research Fellow at Nagasaki University, emphasised that the risk extends far beyond traditional tropical regions. “It’s been widely thought that mosquitoes carrying chikungunya would be confined to subtropical or tropical continents, but our analysis has found that the risk extends way beyond these regions,” she said.
Sushant Sahastrabuddhe, Associate Director General at the International Vaccine Institute, added: “The potential spread of vectors carrying viruses like chikungunya won’t wait for us to carry out years of research. It’s been extremely important that the modelling we’re working on is shared in real time to help public health professionals prepare for the future.”
Senior author Kaja Abbas, Associate Professor at LSHTM and Nagasaki University, highlighted the relevance for vaccination policy. “Our model-based estimates are useful to inform outbreak response immunisation strategies for different age groups using the two licensed vaccines in Brazil and more broadly in any setting globally at risk.”
Climate change could expand future risks
The researchers caution that their maps represent long-term averages and do not fully account for unpredictable future changes. Extreme weather events and climate change may significantly alter mosquito habitats, potentially expanding chikungunya transmission into new regions.
This concern underscores the importance of proactive prevention strategies, including vector control, surveillance, and prioritisation of vaccine rollouts. The study’s findings are expected to inform global health efforts. It will include recommendations from the WHO SAGE Working Group on Chikungunya Vaccines.
Preparing for the next wave
With millions of people at risk annually and a significant portion left with lasting disability, chikungunya poses an urgent global health challenge. The study highlights India, Brazil, and Indonesia as hotspots where the burden could be especially heavy, but the findings also point to emerging risks elsewhere.
In the absence of specific treatments, prevention remains the most effective defence. Coordinated strategies — including mosquito control, improved surveillance, and vaccine deployment — will be critical to reducing the human and economic toll of chikungunya in the years ahead.
