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Influenza Virus — Explained

Influenza, commonly known as the flu, is a contagious respiratory infection caused by the influenza virus. It affects the nose, throat, and lungs, and can lead to mild to severe illness — and in some cases, can be life-threatening.

📌 What Is the Influenza Virus?

The influenza virus is a member of the Orthomyxoviridae family of viruses.

It has a single-stranded RNA genome and is an enveloped virus — meaning it’s surrounded by a protective lipid layer.

The virus is shaped roughly like a sphere or oval with characteristic surface proteins.

⚙️ Key Structural Features

The influenza virus has two important proteins on its surface:

Hemagglutinin (HA)

Helps the virus attach to and enter host cells.

It’s a major target for immune responses and vaccines.

Neuraminidase (NA)

Aids in release of new viruses from infected cells.

Targeted by antiviral drugs like oseltamivir (Tamiflu).

These proteins are why flu viruses are named with terms like H1N1 or H3N2 — referring to different HA and NA types.

🧬 Types of Influenza Viruses

There are three main types that infect humans:

Influenza A

Most common cause of large seasonal outbreaks and pandemics.

Can infect humans and some animals (like birds and pigs).

Influenza B

Causes seasonal outbreaks, primarily in humans.

Usually less severe than Influenza A.

Influenza C

Causes mild respiratory illness and is less common.

🦠 How It Spreads

The flu virus spreads mainly through:

✔ Airborne droplets when an infected person coughs or sneezes
✔ Touching contaminated surfaces, then touching the face
✔ Close contact with infected individuals

🩺 Symptoms of Influenza

Common symptoms include:

Fever and chills

Cough and sore throat

Runny or stuffy nose

Muscle or body aches

Fatigue (tiredness)

Headache

Some people, especially young children, older adults, and those with weak immunity, may develop complications like pneumonia.

💉 Prevention & Protection

✔ Annual flu vaccination — best protection
✔ Wash hands regularly
✔ Cover coughs and sneezes
✔ Avoid close contact with sick people

🧠 Why It Changes Every Year

Influenza viruses frequently mutate — especially the HA and NA proteins.
This constant change means the immune system may not fully recognize new strains, which is why:

➡ New vaccines are needed each year.