2025’s global health polycrisis: Climate, contagion and the limits of our defences

In 2025, global public health faced a “polycrisis” as once-controlled diseases resurfaced alongside novel threats, proving that health is inextricably linked to climate and environmental stability.

The year witnessed a dramatic redrawing of the global disease map: warming temperatures pushed vector-borne illnesses like dengue into high-altitude regions of Nepal and Ethiopia while South Asia and Brazil faced record-breaking outbreaks.

Simultaneously, declining vaccination rates triggered major measles resurgences across Europe and the US while Africa struggled with intense mpox clusters and Latin America investigated new zoonotic threats.

The resurgence: Old foes, new frontiers

Dr Sandeep S. Reddy, consultant lead, Department of Infectious Diseases at Ramaiah Memorial Hospital (Bengaluru) said that the surge of emerging infectious diseases, driven by the convergence of climate change, ecosystem disruption and intensified human-animal contact has transformed ‘One Health’ from a theoretical concept into an essential governance framework.

Since nearly three-quarters of these infections are zoonotic, traditional siloed health approaches are now inadequate against the expansion of vector-borne diseases, antimicrobial resistance and vaccine-preventable resurgences, he said.

Consequently, global health strategy has shifted toward integrated surveillance and upstream interventions such as land-use and climate policy, necessitating interdisciplinary data sharing and targeted capacity investment in the Global South, Dr Reddy said.

Climate change becomes a direct health emergency

If 2025 had a single unifying driver of health crises, it was climate change. Record-breaking heatwaves swept across India, the West Asia and southern Europe, pushing heat-related hospital admissions in cities like Delhi, Cairo and Rome to historic highs. Cardiovascular events, kidney failure and strokes surged during extreme temperature spikes.

Flooding compounded the crisis. Historic deluges in East Africa and South Asia triggered outbreaks of cholera, leptospirosis and diarrhoeal diseases, overwhelming fragile health systems in Somalia, Bangladesh and Myanmar.

Air pollution remained a constant backdrop to disease. The WHO continued to estimate that around seven million premature deaths annually are linked to polluted air, particularly in megacities across India, China and parts of Africa.

Dr Jothi Neeraja, founder and managing director of People Tree Hospitals and Maarga Mind Care said air pollution in 2025 emerged not just as a respiratory and cardiovascular risk but as a growing mental health threat. “Prolonged exposure to fine particulate matter, she said, is increasingly linked to anxiety, depression, sleep disturbances and cognitive decline due to inflammation and oxidative stress affecting brain function.”

“Beyond biology, she said pollution reshaped daily behaviour, restricting outdoor movement, limiting social interaction and contributing to fatigue and irritability. For people with pre-existing mental health conditions, pollution often worsened symptoms, triggering panic, health anxiety and chronic stress.”

Mental health crisis deepens quietly

While infectious diseases dominated headlines, a parallel mental health crisis intensified. The WHO flagged worsening outcomes among adolescents and young adults, driven by economic uncertainty, conflict-driven displacement, climate anxiety and hyperconnected digital lives. UNICEF estimates showed rising youth suicide rates in at least 11 countries.

Tarun Gupta, Co-founder of mental health platform Lissun, said global statistics mirrored realities on the ground. “One in seven adolescents’ lives with a mental health condition, while suicide remains among the leading causes of death for people aged 15 to 29. In India, exam hubs such as Kota highlighted the pressures faced by young people living away from home under intense academic stress.” He said the crisis demands stronger prevention, school-linked support systems and community-rooted care.

Ramya Yellapragada, Founder & CEO of Marbles Health, argued that 2025 forced a shift away from traditional chemical-only treatments. “If medication alone were enough for mental illness, it would be a solved problem by now,” she notes. Yellapragada highlights a move toward addressing the brain as an electrochemical organ.

“Mental illness disrupts both chemical and electrical balance. Evidence now shows that directly rebalancing electrical networks through non-invasive neuromodulation is often more effective, safer, and faster-acting than relying solely on pharmaceuticals.”

Antibiotic resistance reaches the bedside

In 2025, antimicrobial resistance moved from academic warnings to frontline emergencies. Hospitals across Asia, Europe and South America reported outbreaks of bacteria resistant to last-resort antibiotics. Drug-resistant tuberculosis surged in Central Asia and parts of Africa, driven by treatment delays and funding gaps, while multidrug-resistant gonorrhoea emerged as a growing threat.

Dr Gunisha Pasricha, Associate Director – Research Services, Infectious Disease Genomics at MedGenome, said declining vaccination rates, sustained polio transmission and accelerating antimicrobial resistance exposed just how fragile global health defences remain. She said that metagenomic next-generation sequencing and long-read sequencing technologies advanced rapidly in 2025, enabling faster identification of pathogens in unexplained infections. Genomics, supported by AI-enabled interpretation, is moving closer to real-time clinical decision-making, she said, calling tuberculosis genomic surveillance a public health imperative.

A year that reset global health priorities

Despite the setbacks, 2025 also delivered hope. AI-driven diagnostics reduced errors and turnaround times, personalised cancer therapies showed strong trial results, and regenerative medicine moved closer to real-world use.

Yet the year will be remembered less for individual outbreaks than for the warning it delivered. Infectious diseases, climate stress, mental health, chronic illness and health inequity are no longer separate crises, they are deeply connected.

As the world heads into 2026, experts say the real test will be whether governments turn 2025’s hard lessons into long-term investments: integrated surveillance, climate-resilient health systems, universal vaccination coverage and accessible mental healthcare.

According to Sagar Sen, senior VP at Qure.AI., 2025 was defined by the “pragmatic adoption” of AI. “Hospitals moved away from broad experimentation and focused on AI that tangibly supports daily operations—from early detection in high-volume environments to reducing administrative burdens like scheduling and documentation,” Sen says. He notes that the shift was not about replacing clinicians, but about using AI to extend care beyond hospital walls through digital triage and remote monitoring, effectively clearing massive diagnostic backlogs.

Respiratory infections stage a confusing comeback

Even as the world moved past the immediate trauma of COVID-19, respiratory pathogens returned with unexpected force. A global surge in infections including human metapneumovirus (hMPV), influenza and RSV put hospitals under renewed strain. China and parts of Europe reported unusually high paediatric pneumonia admissions while urban hospitals in the United States faced prolonged winter bed shortages.

RSV hit older adults hard despite the availability of new vaccines and mismatched flu vaccine strains in countries such as Canada, Japan and the UK worsened hospital congestion. As infectious disease experts warned, uneven immunity, waning masking habits, increased travel and volatile winters created ideal conditions for viral spread.

Cancer and chronic diseases shift younger

Perhaps the most unsettling non-communicable disease trend was the rise in cancers among younger adults. Colorectal cancer cases climbed sharply among people under 50 across the US, Europe, Japan and India, while breast cancer continued to grow in regions with delayed screening uptake.

At the same time, cardiologists across Asia and the West Asia reported more heart attacks in people under 40, driven by sedentary lifestyles, processed diets, stress and undiagnosed metabolic disorders. Fatty liver disease, hepatologists warned, is fast becoming “the new diabetes”.

Vaccines: promise and hesitation

Vaccination challenges persisted despite scientific breakthroughs. Routine immunisation dips contributed to the return of measles and whooping cough, fuelled by misinformation and political polarisation. At the same time, malaria vaccines expanded in parts of Africa, dengue vaccines rolled out in India, Thailand and Brazil, and RSV vaccines gained momentum among older adults in Western countries. The contrast highlighted a central paradox of 2025: scientific progress outpacing public trust.

The 2026 outlook: Medtech, AI and investment realities

As we look toward the new year, the “One Health” framework, integrating human, animal and environmental surveillance has moved from theory to practice.

However, the future depends on capital. Ajay Mahipal, co-founder & general partner (HealthKois) said that healthcare funding has become tighter and more outcomes-focused.

“In 2026, investor evaluation is cantered on whether AI can operate as core healthcare infrastructure,” Mahipal said. “Capital is likely to favour solutions that deliver hard, defensible ROI against rising medical cost inflation.”

This shift toward ROI is already visible in how technology is procured. Sagar Sen, senior VP at Qure.AI. observed that healthcare systems are now prioritising “system fit and long-term value” over hype. As workforce shortages persist, AI and robotics are being integrated as “core infrastructure” to ensure speed and consistency in treatment delivery, signalling a 2026 where healthcare moves from episodic diagnosis to continuous, proactive, system-led care.

Across healthcare, 2025 marked a shift from experimental innovation to patient-centric, real-world solutions. Sarvesh Mutha, managing director of IntegriMedical, said medtech is increasingly focused on comfort, safety and accessibility.

“Needle-free injection technologies emerged as a standout breakthrough across paediatrics, vaccines, fertility and chronic care, reducing pain, anxiety, needle-stick injuries and biomedical waste. As injectables continue to dominate drug delivery, non-invasive technologies are improving patient compliance and experience.”

Eyes, climate and technology intersect

Climate change also left visible marks on eye health. Dr Himanshu Shekhar, group chief strategy officer at ASG Eye Hospital said rising temperatures, ozone depletion and air pollution were increasing the burden of cataracts, dry eye disease, conjunctivitis and retinal disorders.

“Climate change is increasingly emerging as a crucial risk factor for eye health. Climate-driven ozone depletion is intensifying exposure to harmful UVB radiation, which is a proven trigger for cortical and nuclear cataracts. Studies from high-UV regions, including India’s coastal areas, show cataract rates up to 20% higher, with odds ratios rising sharply among those with prolonged sun exposure,” Dr Shekhar added.

“Rising temperatures are also destabilising the tear film, leading to a surge in dry eye disease, particularly in urban populations. Exposure to air pollutants such as PM2.5 and ozone inflames the ocular surface, worsening symptoms like redness, irritation and conjunctivitis. Heatwaves above 28.7°C have been linked to a 16% spike in conjunctivitis cases, while longer pollen seasons are fuelling allergic eye disorders.”

“Erratic weather patterns, changes in humidity and wildfire-related air pollution are contributing to infections such as trachoma, acanthamoeba keratitis and viral reactivations. At the same time, chronic pollution exposure is accelerating cataracts through oxidative stress and increasing the risk of glaucoma, macular degeneration and pterygium.”

“Protective measures such as UV 400+ sunglasses, lubricating eye drops and maintaining adequate indoor humidity are becoming essential. However, addressing the growing burden of climate-linked eye disease will ultimately require stronger public health interventions and wider access to eye care.”

Yet ophthalmology also showcased how technology can close access gaps, said Dr Shekhar, adding that AI-driven predictive diagnostics are enabling early detection of diabetic retinopathy and glaucoma often before symptoms appear, helping prevent blindness in millions.

“Offline-first AI models operating without internet connectivity are transforming rural screening, with 2025 trials showing smartphone-based glaucoma and diabetic retinopathy AI matching specialist performance. Cost-effective robotic assistance in eye surgery is also standardising better outcomes, reducing errors and recovery times.”