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Medically Verified By: Dr. Vikas Mittal, Director, Pulmonologist at CK Birla Hospital, Delhi
Influenza A, B, C Or D: Influenza or flu is a highly contagious respiratory infection that is caused by influenza viruses of type A, B, C or D. Many people experience symptoms ranging from mild to severe, such as cough, runny nose, fever, headache, fatigue and more. Generally, many recover quickly in a few days or less than two weeks, but prolonged respiratory illness can develop complications such as pneumonia that can be life-threatening and result in death. With the growing number of cases of different types of flu or influenza, a lot of people are left confused about the strains. To help you identify which influenza is affecting you and stay safe from the deadliest type of flu this season, we've explained everything below.
Influenza A is an acute respiratory viral infection (ARI) that is caused by influenza A virus H1N1 and H3N2. People who contract influenza A often show symptoms like cough, chills, runny nose, sore throat, headache, high fever and muscle pain. Healthcare professionals outline that most influenza symptoms are mild and typically go away on their own in less than one week. However, if the symptoms get severe with a persistent high fever of 38 C or higher for 7 to 10 days, then they must seek medical attention at the earliest. Influenza A symptoms can lead to serious health complications such as severe pneumonia, shortness of breath, rapid breathing, respiratory failure, seizures and death in people with certain medical conditions.
Influenza B is a flu that is caused by the influenza B virus and belongs to the Yamagata or Victoria lineage. According to the Centers for Disease Control and Prevention (CDC), Influenza A and Influenza B are responsible for the majority of seasonal illnesses during the cold season. Additionally, influenza B can only be spread from human to human, and it is as severe as other influenza, estimating 23 per cent of influenza illnesses across the globe.
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According to the World Health Organisation (WHO), the Influenza C virus is not as common as the previous two viruses and it causes mild infections. Influenza C does not appear to cause epidemics. Additionally, influenza D is common in cattle and does not seem to infect humans.
Influenza symptoms can range from mild to severe, depending on person to person. However, Medical News Today outlines that the following symptoms are some common flu signs:
Additionally, people with certain medical conditions may experience the following symptoms:
Influenza spreads easily from human to human while a person sneezes, talks or coughs by releasing respiratory droplets containing viruses that infect people in close proximity. The recent increase of influenza in India is H3N2, which mainly affects people over the age of 65 and children under five years old.
"Influenza A and B cause most seasonal flu. Influenza A is usually more severe and responsible for pandemics, while B is milder but still serious. Influenza C causes mild, cold-like illness, and D mainly affects cattle," Dr. Vikas Mittal, Director, Pulmonologist at CK Birla Hospital, Delhi, explains. "Clinically, symptoms overlap, so RT-PCR testing for flu panel on a throat and nasal swab is the only reliable way to identify the type. Influenza A is considered the deadliest due to higher complications and mortality risk."
The pulmonologist notes that flu spreads easily in winter due to crowded indoor spaces, low humidity, and reduced immunity. She said, "The virus survives longer in cold, dry air and transmits efficiently through droplets and aerosols. Low vaccination uptake, frequent travel, and poor respiratory hygiene have further amplified transmission, making flu outbreaks appear more widespread and intense this season."
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