New Delhi: The seasonal influenza patterns are shifting this year, with the A(H3N2) subtype emerging earlier and spreading more actively across multiple regions, from the northern hemisphere to India.
Traditionally associated with cooler months and peaking in late autumn and winter, influenza activity is now rising well ahead of expected seasonal timelines. Surveillance data from the World Health Organization’s Global Influenza Surveillance and Response System indicates increasing influenza circulation, particularly of H3N2 viruses, outside typical peak months.
In India, especially in urban centres such as Delhi-NCR and Bengaluru, clinicians are observing a noticeable rise in influenza-like illnesses. A significant proportion of households are reporting symptoms consistent with H3N2 infection. Doctors describe patients presenting with persistent fever, dry cough and throat infections. This year, however, symptoms appear to be lasting longer than usual. Medical specialists report that some individuals continue to experience a dry, irritating cough for more than six weeks after the acute infection has resolved, attributing this to airway inflammation and bronchial hyper-reactivity triggered by the virus.
Experts link the early surge to multiple converging factors, including erratic seasonal transitions, immune stress, behavioural changes following pandemic restrictions, and environmental influences. The rapid shift from winter to summer in cities like Bengaluru may also be contributing to increased viral transmission.
New Variant
Globally, influenza activity began climbing in the latter half of 2025, with H3N2 viruses predominating over other circulating strains. Of particular concern is the emergence of a new A(H3N2) variant known as ‘subclade K’, which has become increasingly dominant. Researchers first detected this variant in October, after vaccine production for the current season was already underway, leaving little time for its inclusion in existing formulations.
Medical researchers have noted that subclade K acquired several new mutations over a short period, making it antigenically distinct from the H3N2 strain included in this year’s vaccines. Infectious disease specialists explain that these genetic changes may allow the virus to spread more efficiently across populations, even if it does not necessarily cause more severe illness on an individual basis. Its higher transmissibility, however, has led to a sharp rise in overall case numbers and earlier-than-usual influenza activity.
The mismatch between circulating viruses and the strains included in the current northern hemisphere vaccines initially raised concerns among public health experts. However, infectious disease authorities emphasize that influenza vaccines continue to provide meaningful protection even when the match is not perfect.
Clinical data from Canada show that the most recent flu vaccine reduced the risk of outpatient medical visits due to influenza A(H3N2) by approximately 40% compared to unvaccinated individuals. Experts stress that decades of evidence demonstrate that influenza vaccination significantly lowers the risk of hospitalization, intensive care admission and death, even during seasons of partial mismatch.
WHO Recommendations
In response to global surveillance findings, the World Health Organization has issued updated recommendations for the 2026-27 northern hemisphere influenza season. The agency has advised that vaccine manufacturers revise the H1N1, H3N2 and B/Victoria components to better match currently circulating strains, including the new H3N2 subclade K variant. Because influenza vaccine production requires at least six months from strain selection to distribution, these recommendations are issued well in advance of immunization campaigns, which typically begin in late summer or early autumn.
India, as part of the northern hemisphere, follows WHO guidance when determining vaccine composition. Indian regulators are expected to review and approve the updated formulation, allowing domestic manufacturers to align production schedules to ensure availability before peak transmission in the upcoming season.
While India does not operate a universal influenza vaccination programme, medical authorities reiterate the importance of annual vaccination for high-risk groups. Elderly adults, pregnant women, healthcare workers, young children, immunocompromised individuals, and adults over 50 with underlying health conditions are strongly advised to receive the flu shot ahead of winter. Seasonal influenza is responsible for an estimated 290,000 to 650,000 respiratory deaths globally each year, underscoring the ongoing public health burden.
Health experts caution that although subclade K is spreading rapidly, vaccination remains the most effective tool for reducing severe disease and healthcare strain. They emphasize that even in years of viral evolution and shifting seasonal patterns, updated vaccines continue to play a critical role in protecting vulnerable populations and limiting complications.