If you are experiencing symptoms such as headache, body ache, cold and fever, might be you are down with H3N2 influenza. It is a seasonal flu strain that tends to spread rapidly, particularly during weather transitions. While its symptoms may initially resemble those of a common cold, the condition can quickly worsen if left untreated. According to the health experts, it was started with just the Delhi-NCR region, now entire India is experiencing an increase in flu-like symptoms, primarily due to the H3N2 strain, which is a subtype of Influenza A. According to a recent survey, about 70% of households in Delhi, Gurugram, Noida, Faridabad, and Ghaziabad have at least one family member experiencing symptoms of viral fever, flu, or Covid-like illness.

The early symptoms of H3N2 influenza often include a sudden onset of high fever (typically above 38–39°C) accompanied by chills, along with body aches, fatigue, muscle pain, and headaches. Patients may also experience a sore throat, a persistent dry cough, and nasal congestion or a runny nose. The recent surge in H3N2 flu cases can be attributed to several factors. Post-monsoon weather and fluctuations in humidity create favorable conditions for the virus to survive, while crowded indoor spaces with poor ventilation accelerate its spread Pollution further weakens the lungs and overall immunity, making individuals more susceptible. In addition, frequent virus mutations have made H3N2 more aggressive. Low immunity levels, caused by reduced exposure to flu strains in recent years, also contribute to its spread. Children, the elderly, and people with chronic health conditions remain particularly vulnerable.

Dr Shuchin Bajaj, Founder and Director Ujala Cygnus Healthcare Services, has answered all the burning questions about the H3N2 virus. Let's try to understand what the virus is, what signs to watch out for and more.

1. How does the H3N2 virus spread?

H3N2, like other influenza viruses, spreads mainly through respiratory droplets released when an infected person coughs, sneezes, or even talks. The virus can also spread by touching contaminated surfaces and then touching your nose, mouth, or eyes. Crowded indoor spaces, poor ventilation, and close personal contact increase the risk of transmission.

2. What causes H3N2 infection and why is this flu concerning?

H3N2 is a subtype of Influenza A virus. Infection occurs when the virus enters the body through the respiratory tract. It is concerning because:

•   It tends to cause more severe illness compared to some other seasonal flu strains.

•   It affects children, the elderly, and people with comorbidities more strongly, leading to hospitalisations.

•   Seasonal surges can strain healthcare systems, as we’re seeing in Delhi NCR and other regions.

3. Is H3N2 treatable? What are its effects on the human body?

Yes, H3N2 is treatable. Most people recover with rest, hydration, and symptomatic treatment like paracetamol. In higher-risk groups or severe cases, antiviral medicines (like oseltamivir) may be prescribed.

Common effects include fever, cough, sore throat, body aches, fatigue, and nasal congestion. In some patients, especially those with weak immunity, it can lead to bronchitis, pneumonia, and worsening of underlying conditions like asthma or heart disease.

4. How is H3N2 different from other common flu strains? Is the mutation rate of H3N2 higher?

H3N2 differs mainly in its surface proteins (hemagglutinin “H3” and neuraminidase “N2”). These proteins evolve over time, requiring our immune system and vaccines need to keep adapting.

H3N2 is known to mutate relatively quickly, leading to reduced vaccine effectiveness some years. However, all influenza viruses mutate—this is why the flu shot composition is updated annually.

5. How can we prevent H3N2 flu?

H3N2 flu can be prevented through the following measures:

•   Annual flu vaccination – includes protection against H3N2 in most formulations.

•   Masking and hand hygiene – especially in crowded spaces.

•   Avoid close contact with sick individuals.

•   Ensuring good ventilation – keep indoor spaces well- aerated.

•   Boost immunity through adequate sleep, hydration, and balanced diet.

6. Could H3N2 cause the next pandemic?

While H3N2 can cause seasonal outbreaks and hospital surges, it is unlikely to spark a pandemic on the scale of COVID-19. It has circulated in humans for decades, so most people have some baseline immunity, either from past infections or vaccines. Pandemics are caused usually by novel viruses that come into circulation for the first time in human populations. H3N2 is not a novel virus. However, continuous mutation means health authorities keep a close watch. The real risk is that a new, significantly different influenza strain could emerge and spread widely.

If you have any questions related to H3N2 influenza, you can consult a doctor at your nearest Ujala Cygnus Hospital or ask our health experts via email at askadoctor@ujalacygnus.com