H1N1 Returns: Dr Vijay Kumar Agrawal Explains Who Is At Risk, When Flu Turns Serious And How To Treat It

Over the past few weeks, Dr Vijay Kumar Agrawal, Director & HOD, Pulmonology & Sleep Medicine and Senior Consultant, Critical Care Medicine, Yatharth Hospital, Faridabad, has been seeing a familiar pattern return to his outpatient department (OPD), a trend also being reported by doctors elsewhere.

Patients have been arriving with fever, a running or blocked nose, sore throat, cough, headache, body ache and an unusual body temperature of 102–103°F, severe body ache and fatigue, he told The Health Outlook.

The illness being encountered in a large number of these patients is influenza, including H1N1, which has once again begun showing increased activity in several parts of the country.

“Most patients are likely to recover without complications, but influenza should not be dismissed simply because it is a familiar infection. There is no need for panic, but there is certainly a need for awareness,” Dr Agrawal said.

The concern has been heightened by the increase in laboratory-confirmed H1N1 cases in Delhi-NCR. Delhi had reported 1,449 confirmed H1N1 cases by August 12, 2026, compared with 229 during the corresponding period last year, according to reported NCDC data. The number had subsequently risen further, with Delhi's H1N1 tally reported at 1,777 cases by August 22.

Across the NCR, influenza-like illnesses have also been reported by doctors in Gurugram, Faridabad and neighbouring areas. In Gurugram, 21 H1N1 cases had been recorded between January and August, including seven cases in August alone, according to local health reports. Mumbai too has witnessed increased activity, with 309 H1N1 cases reported between June 1 and August 15. Maharashtra had reported 427 confirmed H1N1 cases and four deaths by July 31, according to state data.

However, these numbers need to be interpreted cautiously, Dr Agrawal emphasised. “Laboratory-confirmed cases depend heavily on testing and surveillance. A state reporting fewer confirmed cases cannot automatically be assumed to have less influenza. The actual burden can be higher than the laboratory-confirmed numbers suggest.”

H1N1 Is Not A New Virus

Although H1N1 continues to be popularly referred to as “swine flu”, the terminology can sometimes create unnecessary apprehension.

The H1N1 virus responsible for the 2009 pandemic has been circulating in human populations for many years and is now regarded as one of the established seasonal influenza viruses. Seasonal influenza is primarily caused by influenza A and influenza B viruses. Among influenza A viruses, A(H1N1)pdm09 and A(H3N2) are important strains circulating among humans, while influenza B/Victoria also continues to be detected, explained Dr Agrawal.

Recent Indian surveillance has confirmed circulation of these established influenza strains. Genetic analysis has also indicated broad similarity between circulating viruses and strains included in the WHO-recommended influenza vaccine composition.

“This is important because the present situation should not be described as the arrival of some mysterious new influenza virus,” Dr Agrawal said. “Influenza viruses undergo continuous genetic changes. What is being witnessed now is predominantly increased seasonal influenza activity involving known circulating strains.”

Why Is The Flu Being Seen Now?

Influenza activity does not follow exactly the same pattern throughout India. Unlike countries where transmission is concentrated largely in a single winter season, India has substantial climatic and geographical variation.

According to NCDC surveillance patterns, influenza activity can show peaks during January to March and again during the post-monsoon period, broadly August to October, although the timing and intensity can vary between states.

The present increase in Delhi and NCR has therefore coincided with a period during which respiratory infections can gain momentum.

“August should not necessarily be viewed as the end of influenza activity. The coming weeks need to be watched carefully because the post-monsoon period can support further transmission,” Dr Agrawal added.

Symptoms Can Be Mild — Or Severe

The clinical picture being seen at OPDs has been varied. Fever, sore throat, nasal congestion or a running nose, dry cough, headache, chills, muscle and body aches and considerable fatigue are among the commonly reported symptoms.

Some patients develop high-grade fever, while a smaller proportion may experience nausea, vomiting or diarrhoea. The cough can remain for several days or even weeks after the fever has subsided.

An important difficulty is that H1N1 cannot be reliably distinguished from H3N2, influenza B, Covid-19 or other respiratory infections merely on the basis of symptoms.

“Symptoms overlap considerably. A clinical examination is therefore important, particularly when symptoms are persistent or worsening,” Dr Agrawal said.

For the majority of otherwise healthy individuals, influenza remains a self-limiting infection. Rest, adequate hydration and appropriate symptomatic treatment are generally sufficient.

The situation changes when the infection begins affecting the lungs.

When Can Influenza Become Dangerous?

In a small proportion of patients, influenza can progress from an infection of the upper respiratory tract to viral pneumonia. Secondary bacterial pneumonia can also develop.

Warning signs include breathlessness, rapid breathing, chest pain, falling oxygen saturation, bluish lips, confusion, excessive drowsiness, persistent high fever, severe weakness, inability to maintain hydration and blood in sputum.

Particular attention should be paid when fever initially appears to improve but then returns along with worsening cough, breathlessness or weakness.

“Any patient who develops difficulty in breathing or a fall in oxygen saturation should not wait at home hoping that the illness will settle on its own,” Dr Agrawal warned.

Severe influenza can result in hypoxaemia and, rarely, acute respiratory distress syndrome (ARDS), in which extensive inflammation of the lungs interferes with oxygen exchange and intensive care may become necessary.

Who Needs Greater Protection?

Not every patient faces the same risk.

Greater vigilance is required among children below five years, older adults, particularly those above 65, pregnant women and people living with asthma, COPD, heart disease, diabetes, kidney or liver disease, neurological disorders, cancer or weakened immunity.

Patients receiving chemotherapy, immunosuppressive medicines or prolonged steroid treatment also need greater caution.

“A mild influenza infection in a healthy young adult is very different from the same infection in an elderly person with COPD and diabetes. The threshold for seeking medical advice should be much lower in vulnerable patients,” Dr Agrawal emphasised.

Does Everyone Need An Influenza Test?

'Not necessarily,' Dr Agrawal said as he explained that during established influenza circulation, uncomplicated cases can often be diagnosed clinically. Laboratory testing becomes more useful when patients have severe or progressive disease, require hospitalisation, belong to high-risk groups or have unusual symptoms.

When testing is required, molecular tests such as RT-PCR are generally more reliable than many rapid antigen tests.

However, treatment should not always be delayed while awaiting laboratory confirmation in a seriously ill or high-risk patient when influenza is strongly suspected.

The Antibiotic Trap

According to Dr Agrawal, one of the biggest problems during every influenza season is the tendency to start antibiotics whenever fever and cough develop.

“Influenza is a viral infection. Antibiotics do not kill influenza viruses,” he said.

Medicines such as azithromycin, cefixime or amoxicillin-clavulanate should therefore not be taken automatically for every episode of fever and cough.

Unnecessary antibiotic use can cause side effects and contribute to the growing problem of antimicrobial resistance.

“Antibiotics certainly have a role when a secondary bacterial infection is suspected or confirmed, but they should not become routine treatment for uncomplicated influenza,” he added.

Where Do Antivirals Fit In?

For most healthy people with uncomplicated influenza, treatment remains supportive — including rest, fluids, fever control and other appropriate symptomatic measures.

However, oseltamivir and other influenza antivirals may be required in patients with severe or progressive illness, those who are hospitalised and people at high risk of complications.

Antivirals are generally most effective when started within the first 48 hours of symptoms, although they can still be beneficial later in patients with severe or complicated disease.

“They should be prescribed according to the patient's clinical condition and risk profile rather than taken indiscriminately,” Dr Agrawal said.

Prevention Remains The First Line Of Defence

With influenza activity increasing, simple preventive measures become particularly important.

Patients with fever and acute respiratory symptoms should stay home as far as possible and avoid crowded places, offices, schools and social gatherings while they are unwell. Coughs and sneezes should be covered, hands washed frequently and unnecessary touching of the eyes, nose and mouth avoided.

Ventilation also matters. Opening windows and increasing the flow of outdoor air can help reduce the concentration of respiratory particles in enclosed spaces.

A person with fever and cough who must interact with others should consider wearing a well-fitting mask, particularly around elderly people, young children, pregnant women and immunocompromised individuals.

“Influenza prevention is not dependent only on hospitals and doctors. Much of the transmission can be reduced through responsible behaviour at home, workplaces and public spaces,” Dr Agrawal said.

Should People Take The Flu Vaccine?

Annual influenza vaccination remains particularly important for people at higher risk of severe disease.

Because influenza viruses continually evolve, vaccine composition is reviewed and updated regularly. The 2026–27 WHO-recommended Northern Hemisphere trivalent vaccine includes components targeting H1N1pdm09, H3N2 and B/Victoria.

Vaccination does not mean that a person can never develop influenza. Its important benefit lies in reducing the risk of severe disease, complications and hospitalisation.

Older adults, pregnant women, young children and people with chronic lung, heart or metabolic diseases should discuss annual influenza vaccination with their doctors. Healthcare workers, because of their repeated occupational exposure, should also consider vaccination.

What Can Be Expected In The Coming Weeks?

The current increase needs to be monitored rather than sensationalised.

With the post-monsoon period extending through the coming months, influenza and other respiratory viruses may continue circulating. Schools, workplaces, crowded indoor environments, changing temperatures and increased indoor activity can all influence transmission.

“It would be premature to predict the size of the coming peak. What is needed is continued surveillance, timely testing of appropriate cases and preparedness in hospitals,” Dr Agrawal said.

Stay Alert, Not Afraid

The overwhelming majority of people infected with seasonal influenza will recover completely. But a common infection should not be mistaken for a harmless infection in every individual.

“My message to patients is simple: do not panic, but do not ignore the warning signs,” Dr Agrawal said. “Avoid unnecessary antibiotics, protect vulnerable family members, seek medical attention when symptoms worsen and use antiviral treatment when it is clinically indicated.”

The best response to the current H1N1 activity is therefore neither fear nor complacency. As Dr Agrawal puts it, “It is awareness, timely medical care, rational use of medicines, vaccination for those who need it and responsible behaviour to prevent transmission.”