Published Sep 12, 2026 | 7:00 AM ⚊ Updated Sep 12, 2026 | 7:00 AM
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Synopsis: India’s latest influenza surge is being driven by monsoon conditions, humidity, crowded spaces, viral evolution and vulnerable populations, according to doctors. Limited testing also means confirmed H1N1 numbers may capture only part of community transmission. Most cases remain self-limiting, but influenza can cause pneumonia and severe complications in high-risk patients.
Influenza cases have been rising across several parts of India this monsoon, with doctors reporting more patients with fever, cough, sore throat, rhinitis and body aches than they saw during the same period last year.
The increase has been particularly visible in outpatient departments, although the actual number of influenza infections is likely to be higher than confirmed cases because many patients with mild illness are treated without testing.
Doctors said the rise was being driven by a combination of seasonal conditions, transmission in crowded settings, changes in circulating influenza viruses and the presence of underlying illnesses that can make infections more significant.
Dr Sweatha Kumar, Infectious Disease Consultant at Rela Hospitals, Chennai, said influenza transmission can be influenced by three broad factors: the virus, the people it infects and the environment in which transmission occurs.
“We have multiple reasons: the agent factor, the host factor, and the environmental factor. These three are the factors we consider in an epidemiological trial,” she told South First.
The environmental component becomes particularly important during the monsoon, she said.
“Influenza is not restricted to only the shorter winter season. Because of our diverse climate, different regions will peak at different times,” Dr Sweatha said.
“Next, changes in temperature, humidity, and rainfall can also increase viral respiratory infections. These infections most commonly occur in the rainy seasons,” she said.
According to her, India’s seasonal pattern also varies geographically, with respiratory infections appearing at different times as the monsoon moves across the country.
Dr Sweatha said the conditions in which people live, study and work can further increase transmission.
“And as I mentioned, high population density can be a crucial factor. A crowded urban environment, like what is seen at schools, workplaces, and on public transport, can also be an amplifying factor for the transmission,” she said.
She also pointed to how people respond to respiratory symptoms as another factor that can affect transmission and the number of infections that are detected.
“Lack of awareness and lack of testing can also play a part. There is both underreporting and overreporting… There are the issues caused by people self-medicating. And let us not forget the trouble caused by over-the-counter drugs,” she said.
Dr Mohammed Sanowfer, Consultant in the Department of Internal Medicine at KIMSHEALTH, Thiruvananthapuram, said his outpatient department was also seeing an increase.
“We’re seeing a noticeable rise in OPD patients presenting with fever, cough, and influenza-like symptoms compared to the same period last year,” he told South First.
Testing remains an important limitation when looking at influenza numbers.
Dr Sanowfer said most patients with uncomplicated influenza-like illness did not undergo confirmatory testing.
“Testing is largely limited to inpatients. Since rapid molecular tests such as Xpert Xpress Flu/RSV are costly, outpatients with typical, self-limiting illness are usually managed clinically without confirmatory testing,” he said.
“Testing is reserved for those admitted or with red-flag features,” he clarified.
Dr K Vinodini, Senior Consultant Microbiologist at Neuberg Diagnostics, said influenza’s ability to spread should not be underestimated.
“Influenza is certainly not a virus that should be dismissed as just another seasonal infection. Influenza viruses are highly transmissible respiratory viruses, and their behaviour can vary considerably depending on the circulating strain and the individual’s immunity and underlying health status,” she told South First.
This means laboratory-confirmed cases do not necessarily represent every infection circulating in the community.
Dr Vamshi V, Consultant in Internal Medicine at Gleneagles AWARE Hospital, LB Nagar, Hyderabad, described reported numbers as only part of the picture.
“We have to be careful with those numbers. They are really just the ‘tip of the iceberg’. Official reports give us an idea of the trend, but they don’t tell the whole story,” he told South First.
“Since most mild cases are treated symptomatically without testing, the actual number of people circulating with the virus in the community is almost certainly much higher than what shows up in the official data,” Dr Vamshi said.
Dr Sweatha said seasonal changes in the virus could contribute to the increase.
“Seasonal antigenic drift also can contribute to this,” she said.
Antigenic drift refers to small changes that occur in influenza viruses as they circulate.
Dr Vinodini said the behaviour of influenza could differ depending on which strain was circulating and the health of the person infected.
“While many healthy individuals recover uneventfully, infection can progress to lower respiratory tract disease, viral or secondary bacterial pneumonia and, in vulnerable individuals, severe systemic complications,” Dr Vinodini said.
Dr Sweatha also stressed how underlying illnesses were an important part of the epidemiological picture.
“India is the diabetic capital of the world. And diabetic individuals are more prone to pneumonia and flu infections,” she said, also pointing to India’s large population and the presence of the elderly.
She said several chronic conditions could increase the risk associated with influenza.
“And we have a lot of patients who have chronic obstructive pulmonary disease, asthma, asthmatics, who have cardiovascular disease, kidney disease, liver patients, pre- and post-transplant patients. And all those will contribute to the increased risk,” she said.
Dr Sanowfer said the cases he was seeing involved different age groups rather than one clearly dominant group.
“Children, young adults and older adults are all presenting in meaningful numbers this season,” he said.
Dr Sanowfer said most uncomplicated infections remained self-limiting.
“The typical picture is fever, sore throat, rhinitis and cough. Most uncomplicated cases recover within 5–7 days with symptomatic management,” he said.
But complications were more concerning in certain groups. Dr Sanowfer said prolonged fever and breathing difficulty were among the presentations doctors watched for in high-risk patients.
“We are seeing complications, though mainly in specific risk groups: elderly patients with comorbidities, pregnant women and obese patients. In these groups, pneumonia, breathing difficulty and prolonged fever are the concerning presentations we watch for,” he said.
Dr Vamshi said most patients continued to recover within a week, but hospitals were seeing more serious illness among vulnerable patients.
“The main things sending people to the hospital right now are viral pneumonia, breathing issues in patients who already have asthma or chronic obstructive pulmonary disease, secondary bacterial infections, and, in severe cases, acute respiratory distress syndrome,” he said.
Dr Vamshi described the current situation as increased seasonal influenza activity, with localised surges rather than a widespread outbreak across the country.
“I’d call it a seasonal surge. India typically sees two main flu peaks every year, one during the monsoon, August–October, and one in the winter, January–March,” he said.
Dr Sweatha’s explanation also points to why the timing of influenza can differ from one part of India to another.
“Because of our diverse climate, different regions will peak at different times,” she said.
For now, doctors said the increase appeared to reflect several factors coming together during the monsoon: favourable environmental conditions, greater opportunities for transmission, changes in circulating influenza viruses, vulnerable populations and the fact that a large proportion of mild infections are never laboratory confirmed.
The rise in reported H1N1 cases, therefore, needs to be read alongside what doctors are seeing in outpatient departments and hospitals, rather than treated as a complete count of influenza infections circulating in India.
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(Edited by Fayisa CA.)
