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The Union Ministry of Health and Family Welfare, with the Department of Health Research, ICMR and NCDC, said on 25 August 2026 that seasonal respiratory illness trends are being tracked through a pan-India surveillance network and there is no cause for alarm.
DHR Secretary and ICMR Director General Dr Rajiv Bahl said the circulating Influenza A (H1N1) viruses are A/Missouri/11/2025 (H1N1) pdm09-like, with haemagglutinin gene analysis placing the isolates in clade 6B.1A.5a2a, subclade D.3.1.1.
This lineage has circulated in India since 2025 and the genetic changes observed are ordinary antigenic drift, not the emergence of a new or dangerous strain.
Genomic and epidemiological surveillance runs through the network of 73 DHR-ICMR Virus Research and Diagnostic Laboratories (VRDLs).
Seasonal influenza was described as largely mild and self-limiting, with the elderly, young children, people with co-morbidities and the immunocompromised advised greater caution.
Influenza viruses change their surface proteins - haemagglutinin (HA) and neuraminidase (NA) - in two very different ways. Antigenic DRIFT is the slow accumulation of small point mutations in the genes coding for those surface proteins, mostly in HA, which is the main target of neutralising antibodies. Drift lets the virus partially escape immunity built from earlier infection or vaccination, and it is the reason seasonal flu vaccine composition is reviewed twice a year. Antigenic SHIFT is an abrupt change caused by reassortment - two different influenza A viruses infecting the same host swap whole gene segments, producing a subtype against which human populations have little or no immunity. Shift is the mechanism behind pandemics; drift is the mechanism behind ordinary seasons. The ICMR statement is precisely a claim that what India is seeing is drift, not shift: the HA gene sits in a known clade and subclade of the same pdm09 lineage that has circulated since 2025.
Simple Analogy: Drift is a familiar face growing a beard - you still recognise it, just less easily. Shift is a stranger walking in wearing someone else's clothes entirely.
Apex body for the formulation, coordination and promotion of biomedical research in India; established in 1911 as the Indian Research Fund Association (IRFA) and renamed ICMR in 1949. Funded by the Government of India through the Department of Health Research.
Department within the Ministry of Health and Family Welfare that funds ICMR and runs the VRDL network under the scheme 'Establishment of a Network of Laboratories for Managing Epidemics and Natural Calamities'. Created by an amendment to the Government of India (Allocation of Business) Rules, 1961 notified on 17 September 2007 and formally launched on 5 October 2007.
Nodal national institute for disease surveillance, outbreak investigation and epidemic response, functioning under the Directorate General of Health Services. Traces its origin to the Central Malaria Bureau set up at Kasauli in Himachal Pradesh in 1909; shifted to Delhi in 1938 as the Malaria Institute of India; renamed National Institute of Communicable Diseases on 30 July 1963; renamed NCDC on 30 July 2009 on completing 100 years.
The global network that tracks circulating influenza viruses and informs the composition of seasonal influenza vaccines. Founded in 1952 as the Global Influenza Surveillance Network (GISN) and renamed GISRS in 2011 when the World Health Assembly adopted the Pandemic Influenza Preparedness (PIP) Framework. It comprises National Influenza Centres, WHO Collaborating Centres, Essential Regulatory Laboratories and H5 Reference Laboratories.
Launched in November 2004 with World Bank assistance to build a decentralised, State-based surveillance system for epidemic-prone diseases so that early warning signals are detected and acted on in time.
Key: Operates through Central, State and District Surveillance Units on a weekly reporting cycle of syndromic (S), presumptive (P) and laboratory-confirmed (L) forms; influenza-like illness is among the conditions it reports.
The web-enabled, near real-time electronic successor to IDSP's largely paper-based reporting, developed by the Ministry of Health and Family Welfare with WHO technical support and rolled out across States from 2019 onwards.
Key: Digitises case-based disease reporting down to the village level, so an outbreak signal can be seen as it builds rather than in retrospective weekly summaries.
Set up by the Department of Health Research to correct India's shortage of specialised viral diagnostic capacity and to provide surge testing during epidemics; the release states that 73 DHR-ICMR VRDLs are carrying out the current influenza surveillance.
Key: Designed in three tiers - regional (Grade I), State-level (Grade II) and medical-college (Grade III) laboratories - so that samples move up the tiers only when advanced characterisation such as genomic sequencing is required.
The 'pdm09' in the virus name is a permanent label: it marks this as a descendant of the strain that caused the 2009 influenza pandemic. That virus was itself a product of antigenic shift and later settled into seasonal circulation - which is why a pandemic-origin virus is today described as ordinary seasonal flu.
Influenza A is a zoonotic virus with reservoirs in birds and swine, and reassortment in a co-infected host is the classic route to a pandemic subtype. This is why animal and human influenza surveillance are increasingly run together under the One Health approach.
The sequencing capability built during COVID-19 - clade and lineage assignment, national consortium reporting - is the same capacity now applied to influenza, which is why a routine flu statement can quote a subclade down to D.3.1.1.
The advisory's 'do not take antivirals or antibiotics without medical advice' is an AMR message: antibiotics do nothing against a viral illness, and indiscriminate antiviral use drives resistance in influenza viruses.
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Health-institution and surveillance questions appear most years in SSC and periodically in UPSC Prelims; drift-versus-shift is a recurring biology and current-affairs crossover.
Gradual accumulation of point mutations in influenza surface protein genes, chiefly haemagglutinin, allowing partial escape from existing immunity.
Abrupt change produced when two influenza A viruses reassort whole gene segments in a co-infected host, generating a subtype new to humans - the pandemic mechanism.
The influenza A subtype that emerged in the 2009 pandemic and now circulates seasonally; 'pdm09' permanently marks its pandemic origin.
A genetically defined branch of a virus family tree; influenza HA clades and subclades are the units WHO uses to describe how circulating viruses relate to vaccine strains.
WHO surveillance case definition - acute respiratory infection with measured fever of at least 38 degrees Celsius and cough, with onset within the last 10 days.
The ILI criteria plus a requirement of hospitalisation; together the two definitions let a country measure both spread and severity.