How toxic air and low vaccination rates are fuelling India’s H3N2 surge – Firstpost

India is witnessing an unusually sharp surge in H3N2 influenza cases this winter, with health systems under growing strain as the virus converges with record levels of air pollution across several major states.

Data from the Indian Council of Medical Research (ICMR) shows influenza positivity rates climbing rapidly from late September, touching 12–13 per cent by November, higher than what is typically seen during seasonal flu cycles.

Public health experts say the current wave of H3N2 influenza is being fuelled not just by colder temperatures but by a complex mix of environmental stressors, immunity gaps following the Covid-19 pandemic, low influenza vaccination uptake and sustained exposure to hazardous air pollution.

The World Health Organisation has repeatedly warned that prolonged exposure to fine particulate matter such as PM2.5 weakens respiratory defences, increasing vulnerability to viral infections and worsening outcomes.

In the Delhi-NCR region and several other urban centres, doctors describe OPDs overflowing with patients presenting prolonged cough, breathlessness and chest congestion, symptoms that often blur the line between pollution-induced respiratory distress and viral illness. States including Kerala, Delhi, Maharashtra, Tamil Nadu, Gujarat and Puducherry are reporting some of the highest caseloads, raising concerns about widespread community transmission.

Against this backdrop, Firstpost spoke to Dr Neetu Jain, Senior Consultant in Pulmonology, Critical Care and Sleep Medicine at PSRI Hospital to understand what is driving this year’s aggressive H3N2 wave, how pollution is intensifying disease severity and what patients, hospitals and policymakers must urgently prioritise to prevent a deeper public health crisis.

What’s fuelling H3N2 surge this winter?

Dr Jain: Beyond the usual seasonal temperature drops, there are many reasons that this year’s rise in influenza is higher than usual. These include poor air quality, increased indoor socialisation, reduced immune response following prior Covid exposure, and lower-than-normal flu vaccination rates. Together, these factors increase susceptibility and accelerate transmission.

Pollution’s role in severity

Dr Jain: Severe pollution irritates and inflames the respiratory tract, weakening the lungs’ protective mechanisms. When someone is exposed to H3N2 during this period, symptoms become more severe. Breathlessness increases, and complications such as bronchitis and pneumonia often requiring hospitalisation become more likely.

Higher complications in smog zones?

Dr Jain: Yes. We are observing prolonged recovery, persistent cough, deeper lower-respiratory involvement, and higher rates of secondary infections in polluted areas. Many patients remain symptomatic for weeks, and pneumonia and severe bronchitis are noticeably more common than in regions with better air quality.

How is this H3N2 wave clinically different from regular seasonal flu?

Dr Jain: This wave is marked by prolonged cough, deeper chest congestion, extreme fatigue and greater shortness of breath. Symptoms often last beyond 10–14 days and a larger proportion of patients develop wheezing or lower-lung involvement, especially when pollution exposure is high.

Which groups face the highest risk and what should they do now?

Dr Jain: Vaccination is critical, along with early medical evaluation and timely antiviral therapy if symptoms develop. High-risk individuals should avoid pollution exposure, wear N95 masks outdoors, maintain good indoor air quality, stay hydrated, and seek immediate care if breathlessness worsens.

Why are certain states reporting disproportionately high caseloads?

Dr Jain:  These states have dense populations, high mobility, varying pollution levels, and relatively low influenza vaccination coverage. Together, these factors enable rapid community spread and a higher number of clinically significant cases.

When should patients seek medical care amid overlapping symptoms?

Dr Jain:  Anyone with sudden high fever, persistent cough, or increasing breathlessness should seek care promptly. High-risk individuals should consult a doctor immediately for early antiviral treatment. Rapid deterioration, dehydration, or breathing difficulty requires urgent medical attention.

With December showing no signs of plateauing, what must hospitals urgently strengthen?

Dr Jain: Hospitals need expanded flu screening, better triage systems, adequate antiviral supplies, oxygen availability, increased staffing, improved diagnostics, stronger referral pathways, and tighter infection control measures.