How Deadly Is H3N2 Flu Compared To Covid-19? Is It Likely To Cause A Pandemic In India? Here's What Experts Say

Symptoms such as fever, cough, breathlessness and pneumonia also occur in people infected with Covid-19. Due to the similarities in symptoms, people are worried if H3N2 is as deadly as SARS-CoV-2.

H3N2 is a subtype of Influenza A virus, which is responsible for seasonal epidemics of disease in people, along with Influenza B. The only influenza viruses known to cause flu pandemics, or global epidemics of flu disease are Influenza A viruses. 

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H3N2 Infection: The H3N2 virus is responsible for most cases of seasonal influenza in India this year. Since the beginning of 2023, H3N2 has been the predominant subtype among the samples testing positive for influenza. The virus has already claimed two lives in the country. 

H3N2 is a subtype of Influenza A virus, which is responsible for seasonal epidemics of disease in people, along with Influenza B. The only influenza viruses known to cause flu pandemics, or global epidemics of flu disease are Influenza A viruses. 

According to the Indian Council of Medical Research (ICMR), H3N2 appears to cause more hospitalisations than other influenza subtypes. The common symptoms of H3N2 infection are fever, cough, breathlessness and wheezing, while pneumonia and seizures are rare symptoms. 

According to the ICMR, 10 per cent of the patients with severe acute respiratory infections affected by H3N2 required oxygen, and seven per cent needed Intensive Care Unit (ICU) support. 

Symptoms such as fever, cough, breathlessness and pneumonia also occur in people infected with Covid-19. Due to the similarities in symptoms, people are worried if H3N2 is as deadly as SARS-CoV-2. Some also fear that H3N2 could result in the next pandemic. 

How deadly is H3N2 infection compared to Covid-19?

According to experts, H3N2 is equivalent to Covid-19 in terms of deadliness.

“I would say it is equivalent to Covid-19 in terms of deadliness. It can also cause pneumonia, low oxygen levels, and if not recognised and treated on time, patients can end up in the ICU and may even require advanced treatments like ventilator support,” Dr. Honey Savla, Internal Medicine, Wockhardt Hospitals, Mumbai Central, tells ABP Live.

However, some experts say severe and critical forms of disease are less with H3N2. 

“Both Influenza and Covid-19 are viral illnesses, but they are totally different in terms of viral families. Fever, chills, cough and cold are common in both while shortness of breath can be experienced more in case of Covid-19 than influenza. Headache, muscle aches are common in both, while fatigue is more in Covid-19. Apart from this, stuffiness of nose, sneezing, sore throat, and loss of smell is seen in both the viral infections. Ear ache, nausea, diarrhoea are again common symptoms of both Covid-19 and H3N2 influenza. In comparison to Covid-19 the symptoms in the vast majority of H3N2 cases are mild. Severe and critical forms of disease are less with H3N2,” Dr. Yash Javeri, Director – Critical care and emergency medicine, Regency Hospital, tells ABP Live.

According to some experts, H3N2 will not affect people much.

“A persistent cough, sometimes accompanied by fever, has been a cause for concern for the past two to three months, with cases reported from across the country. The fresh cases are due to H3N2. The news of H3N2 has raised concerns among the masses, but it is important to educate people and tell the difference between the influenza virus subtype and SARS-CoV-2. Although both H3N2 infection and Covid-19 are caused by contagious viruses, H3N2 would not affect people much,” Dr Shuchin Bajaj, Founder Director, Ujala Cygnus Group of Hospitals.

Dr Bajaj also said that H3N2 is not much of a cause for concern.

“Now, many people are concerned about which virus is more deadly. We would like to inform you that H3N2 is not much of a cause for concern as not many people have been hospitalised so far. Also, the influenza virus won’t affect the lungs much. In the case of Covid-19, the majority of patients suffering from the deadly virus in the second wave had a basic cough to severe pneumonia leading to respiratory failure and even death. That has not been the case with H3N2. It is a seasonal virus and eventually, it will go away,” adds Dr Bajaj. 

The exact origin of SARS-CoV-2 is not known, making it difficult to tackle the virus. Some experts say that H3N2 has not been able to strike the population with as much power as SARS-CoV-2.

“The exact origin of SARS-CoV-2 is still unknown, so this makes it a tough virus to tackle. Although a few lethal cases of H3N2 have been reported, it has not been able to strike with as much power as the novel coronavirus did. There is fear regarding H3N2 infection in public, as lakhs of deaths were reported during the first two waves of the Covid-19 pandemic. So, the news of H3N2 spreading fast has raised concerns among the masses,” Dr. SK Chhabra, HOD – Pulmonary, Primus Hospital, tells ABP Live.

The elderly and people with comorbidities are the ones taking a longer time to recover from H3N2. Also, cardiac symptoms have been observed in some people infected with Covid-19. “Most people who got infected with H3N2 have been recovering, apart from people with comorbidities and extremes of age. Strangely, there has been a significant number of influenza cases coming with cardiac symptoms, and what we call viral myocarditis is being seen quite commonly among those who are hospitalised,” Dr. Shivanshu Raj Goyal, Consultant, Respiratory/Pulmonology & Sleep Medicine, Artemis Hospitals, Gurugram, tells ABP Live.

How dangerous is H3N2?

H3N2 is dangerous for the immunocompromised, especially those with bronchial asthma or any other lung disease. Also, the virus is likely to cause sporadic infections, which means that cases could be reported at irregular intervals, or in different places. 

“It is possible that sporadic infections and even localised outbreaks among people with this virus will continue to occur. It will cause influenza like illness, cough, cold, fever and sometimes pneumonia. It is dangerous for the immunocompromised, especially those who have bronchial asthma or any other lung disease,” says Dr Savla. 

Experts believe that seasonal influenza can also be a serious disease, and lead to complications like pneumonia. Also, certain people, including children, elderly persons and those with comorbidities are at greater risk of H3N2 infection.

“Currently, the severity of human illness associated with H3N2 resembles that of seasonal flu. Keep in mind that even seasonal influenza can be a serious disease. Sometimes seasonal influenza can lead to complications like pneumonia. It also can lead to hospitalisation and even death. The south Indian state of Karnataka reported one death from H3N2, marking the first fatality in India from the influenza virus. Certain people are at greater risk of serious flu-related complications including young children, elderly persons, pregnant women and people with certain long-term medical conditions,” says Dr Javeri.

However, some experts believe that H3N2 has not yet presented itself in a dangerous form.

“The Influenza A subtype has not presented itself in a dangerous form, and most people have been suffering from upper airway issues such as cough, sore throat, and sinusitis with prolonged cough. There is hardly any case of pneumonia in young adults due to H3N2,” says Dr Goyal.

Is H3N2 likely to result in a pandemic in India?

While H3N2 infection results in symptoms similar to those of Covid-19, whether the influenza virus subtype can result in a pandemic is not known. Experts say that H3N2 can cause sporadic outbreaks and even localised outbreaks.

“It can cause sporadic outbreaks or even localised outbreaks,” says Dr Savla.

H3N2 infection has been spreading rapidly in India post Holi, in different parts of the country. This year, the cases of seasonal influenza are more than usual.

One of the major reasons behind the rapid increase in H3N2 cases is the change in weather from cold to warm, according to Dr Javeri.

“A sharp rise in H3N2 influenza cases has been reported in India. The virus leads to respiratory symptoms including persistent cough and many more. A quick change in weather from extremely cold to warm has been identified as one of the major reasons behind this rapid increase in flu symptoms among people. Post Holi, many are experiencing flu-like symptoms. The H3N2 influenza is spreading rapidly in different parts of the country. Though every year, from October to February, such cases are common, this year, however, there are more cases than usual,” says Dr Javeri.

Since humans were not exposed to common circulating viruses in the atmosphere for a long time, in the last three years, their bodies no longer have immunity against those viruses. This could have resulted in an increase in cases. There is a possibility that H3N2 could start spreading rapidly from person to person, according to Dr Javeri.

“Experts view that the sudden fluctuation in the temperature and the increase in heat has rapidly pushed up the allergen count in the atmosphere, which has led to the activation of these viruses.  Another factor might be SARS-CoV-2 itself. Due to SARS-CoV-2, our bodies have developed immunity against that. However, it was not exposed to the common circulating viruses in the atmosphere for the longest time. As a result, our bodies no longer have immunity against such viruses, and thus, cases are on the rise. Influenza viruses are always changing. It is possible the H3N2 could change and begin spreading easily from person to person,” says Dr Javeri.