A sharp rise in H1N1 influenza cases in parts of India has put seasonal flu back in focus. Delhi has reported 1,344 H1N1 cases this season, nearly six times the 229 cases recorded during the corresponding period last year, while Nagpur recently reported its first confirmed H1N1 death of 2026. The increase is particularly important for people living with chronic illnesses. While most otherwise healthy people recover from influenza without serious complications, the infection can be considerably more dangerous for those with heart disease, diabetes, asthma or other chronic lung conditions.

H1N1, or influenza A (H1N1), is now a seasonal influenza virus rather than the pandemic virus it was in 2009. It continues to circulate alongside other influenza strains, including H3N2. (World Health Organization)

As cases rise, doctors say people with underlying health conditions should be especially alert to symptoms and seek medical advice early rather than assuming they have "just another viral fever." "People with chronic diseases may also have a reduced physiological reserve, making it harder for the body to cope with a severe infection," says Dr Pankaj Soni, Principal Director, Internal Medicine, Max Smart Hospital, Saket.

Why H1N1 can be more serious if you have a chronic disease

Influenza places considerable stress on the body. Fever, inflammation, increased heart rate, dehydration and, in severe infections, reduced oxygen levels can put additional pressure on organs that may already have limited physiological reserve.

The World Health Organization (WHO) specifically identifies people with chronic cardiovascular, pulmonary and metabolic conditions, including diabetes, as being at higher risk of severe influenza and complications. (IRIS) Influenza can cause pneumonia and, in severe cases, respiratory failure, sepsis and multi-organ complications. It can also aggravate an existing chronic disease.

1. Heart disease: Flu can put additional stress on the heart

People with coronary artery disease, heart failure and other cardiovascular conditions need to take influenza symptoms seriously. During an infection, inflammation and fever increase the body's demand for oxygen. If oxygen levels fall because of respiratory involvement, the cardiovascular system may face additional stress.

Influenza has also been linked to acute cardiovascular events. Research cited by the US Centers for Disease Control and Prevention (CDC) has found that the risk of heart attack can increase substantially in the period immediately following an influenza infection. For someone with existing heart disease, symptoms such as persistent fever, breathlessness, chest discomfort, unusual fatigue or palpitations should therefore not be dismissed as routine flu symptoms.

"Early medical assessment is particularly important if symptoms are worsening," says Dr Soni.

Also Read: H1N1 Cases Spike Nearly Six-Fold In Delhi: Who Is At High Risk And What Are The Complications?

2. Diabetes: Why flu can disrupt blood sugar

Diabetes can make it harder for the body to respond effectively to infections. At the same time, the stress caused by an infection can push blood glucose levels higher. This creates an additional challenge during influenza. A person may eat less because of fever or nausea while simultaneously experiencing elevated glucose levels because of the body's stress response.

WHO lists diabetes among the chronic conditions associated with a higher risk of severe influenza. People with diabetes who develop flu should monitor their blood glucose more closely, maintain adequate hydration and follow their doctor's individual sick-day instructions.

Dr Soni says persistent vomiting, inability to eat or drink, very high or unusually low blood glucose levels, or increasing drowsiness should prompt medical attention. Patients should also avoid stopping or changing prescribed diabetes medication on their own simply because they have influenza. Treatment adjustments, particularly during poor food intake or significant changes in glucose levels, should be discussed with a doctor.

3. Asthma and COPD: Why breathing problems can worsen

For people with asthma, COPD and other chronic respiratory diseases, influenza poses a particular concern because it directly affects the respiratory tract. "Influenza can directly affect the respiratory system and may trigger worsening of the underlying disease," Dr Soni says.

Flu can trigger asthma exacerbations and worsen COPD symptoms. In more severe cases, influenza can cause viral pneumonia or make a person vulnerable to secondary bacterial pneumonia. People with chronic lung disease should continue their prescribed inhalers unless their doctor advises otherwise.

Increasing breathlessness, worsening wheezing, falling oxygen saturation or difficulty speaking because of breathlessness are warning signs that require prompt medical assessment.

What should high-risk people do as H1N1 cases rise?

The current rise in cases makes prevention particularly important for people with chronic illnesses. Annual influenza vaccination is one of the most important preventive measures for people at higher risk. WHO recommends influenza vaccination for people with underlying chronic conditions because they are more likely to develop severe disease.

The National Centre for Disease Control (NCDC), Ministry of Health and Family Welfare, also maintains dedicated seasonal influenza/H1N1 guidance, including recommendations covering high-risk patients, clinical management, home care and vaccination.

Other precautions include:

  • Avoiding close contact with people who have flu-like symptoms
  • Wearing a well-fitting mask in crowded or poorly ventilated settings when influenza transmission is high
  • Improving ventilation indoors
  • Washing hands regularly
  • Covering the mouth and nose when coughing or sneezing
  • Staying home when unwell

WHO's 2026 guidance also highlights ventilation and avoiding crowded, enclosed spaces as measures that can reduce influenza transmission.

Also Read: Symptoms Of H1N1 Virus: Day-1 Warning Signs That Differentiate It From A Common Cold

Don't wait too long to ask about antiviral treatment

For people at high risk of complications, early medical evaluation matters because antiviral medicines may be recommended when influenza is suspected. "Antiviral treatment such as oseltamivir may be recommended early for people at high risk of complications when influenza is suspected, and treatment should not necessarily be delayed while waiting for laboratory confirmation," says Dr Soni.

WHO recommends antiviral treatment for people at higher risk of severe influenza, with the greatest benefit when treatment is started early, ideally within 48 hours of symptom onset. However, this does not mean people should self-medicate with oseltamivir. A doctor should decide whether antiviral treatment is appropriate based on symptoms, risk factors, timing and clinical condition.

Antibiotics, meanwhile, do not treat influenza because H1N1 is caused by a virus. They may be prescribed only when a bacterial infection or secondary bacterial pneumonia is suspected.

The current H1N1 rise in India is a reminder that seasonal influenza should not be underestimated, particularly by people already living with chronic disease. For people with heart disease, diabetes, asthma or COPD, influenza can aggravate an underlying condition and increase the risk of serious complications.

"Influenza should not be treated as 'just another viral fever'," says Dr Soni. "Early recognition, timely medical evaluation, vaccination and appropriate antiviral treatment can significantly reduce the risk of severe complications."

With H1N1 activity rising in several parts of India, the most important message for high-risk patients is simple: know your risk, protect yourself and do not ignore symptoms that are severe, persistent or worsening.



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