Understanding Influenza: Symptoms and Prevention

Influenza (known as flu) is a highly contagious respiratory infection caused by influenza viruses that spread easily through coughing, sneezing, or close contact with an infected person. The disease affects millions of people worldwide each year and often leads to seasonal flu outbreaks.

After understanding the widespread impact of influenza, it's important to recognize the symptoms and who may be most at risk. Symptoms of influenza can range from mild to severe and may include fever. While most people recover within a week, flu infections can become serious or life-threatening for vulnerable groups.

Types of Influenza

Influenza viruses are grouped into several types that cause seasonal outbreaks: types A, B, C, and D. Among them, influenza A and influenza B are the most common in humans.

1. Influenza A

Influenza A is the most common and diverse type of influenza virus. It can infect humans and various animals, including birds (avian influenza) and pigs, and is the main cause of flu pandemics in history. 

Influenza A tends to mutate rapidly, which can reduce vaccine effectiveness and make it harder to control. Studies in the United States (2016–2020) found that influenza A (H3N2) caused the highest disease burden, resulting in millions of illnesses and hospitalizations.

2. Influenza B

Influenza B affects only humans and tends to circulate among children and adolescents. While it doesn’t cause pandemics, it can still lead to significant seasonal outbreaks. Vaccination plays a crucial role in reducing cases and has been shown to prevent a high percentage of hospitalizations in both children and adults under 65.

3. Influenza C and D

Influenza C infections are generally mild and rarely occur in humans, often causing cold-like symptoms. Meanwhile, Influenza D mainly affects cattle and is not known to infect humans.

Symptoms

Symptoms of influenza usually appear 1–2 days after exposure to the virus. Common influenza symptoms include:

• Sudden high fever
• Dry cough
• Headache
• Muscle and joint pain
• Fatigue or general weakness
• Sore throat
• Runny or stuffy nose

Coughing can last up to two weeks or longer. While most people recover without medical treatment, severe cases can lead to hospitalization or death, particularly in high-risk individuals with weakened immune systems or chronic health conditions.

Transmission

Influenza spreads through respiratory droplets released when an infected person coughs or sneezes. The virus can also spread by touching contaminated surfaces and then touching your eyes, nose, or mouth. 

To reduce the risk of transmission, cover your mouth and nose when coughing or sneezing, wash your hands frequently, and avoid close contact with people who are sick.

In tropical climates, influenza can occur throughout the year, while in temperate regions, it peaks during the winter season. The incubation period or the time between infection and the appearance of symptoms is typically 1 to 4 days.

Treatment and Prevention

Most cases of influenza resolve naturally within a week. People with mild symptoms should stay home to avoid infecting others, rest and stay hydrated, use fever-reducing medications if necessary, and seek medical help promptly if symptoms worsen or if part of a high-risk category.

The best protection against influenza is annual vaccination. Safe and effective vaccines have been used for over six decades, and yearly vaccination is recommended because immunity can decrease over time.

Who should get the vaccine annually?

• Pregnant women
• Children aged 6 months to 5 years
• Adults aged 65 and above
• People with chronic health conditions
• Healthcare workers

Other ways to prevent influenza:

• Wash and dry hands regularly.
• Cover your mouth and nose when coughing or sneezing.
• Dispose of tissues properly.
• Stay home when feeling unwell.
• Keep distance from people showing flu symptoms.

Influenza may sound ordinary, but it can be more severe than you think. Understanding it, helps raise awareness and encourage timely prevention. Annual vaccination along with simple habits remains the most effective way to reduce the spread. Protecting yourself also means protecting those around you. 

Sources

Centers for Disease Control and Prevention. (2024). Types of influenza viruses. U.S. Department of Health & Human Services. 

Morris, S. E., Mathis, S. M., Chung, J. R., Flannery, B., O’Halloran, A., Cummings, C. N., Garg, S., Lu, P.-J., Santibanez, T. A., Reed, C., Biggerstaff, M., & Iuliano, A. D. (2025). Estimating historical disease burden and the impact of vaccination by influenza type and subtype in the United States, 2016–2020. Vaccine: X, 26, 100700. 

World Health Organization. (2024). Influenza (seasonal).