Winter is a high-incidence season for influenza. The cold and dry climate seems to create the perfect environment for the flu virus to thrive and spread. According to data from the U.S. CDC, 1.8 out of every 100,000 people die from the flu, and the death rate from flu-related pneumonia reaches as high as 14.1 per 100,000 people.

The flu is no trivial matter—understanding the illness and identifying high-risk groups prone to severe complications is crucial.

Common Symptoms of Influenza

Flu symptoms typically appear about two days after exposure to the virus. Symptoms often come on suddenly and include high fever (above 38°C/100.4°F), severe dry cough, headache, muscle and joint pain, extreme fatigue, and an inability to get out of bed. Other symptoms may include sore throat, runny or stuffy nose, chills, loss of appetite, and even eye socket or eye pain. These symptoms are generally more severe than those of the common cold and can significantly impact daily life.

The Course of Influenza

Flu usually lasts for several weeks and shows different symptoms at different stages:

• Days 1–3: Sudden onset of fever, headache, muscle aches, fatigue, accompanied by dry cough, sore throat, and nasal congestion.

• Day 4 onward: Fever and muscle pain may begin to subside, but sore throat, cough, and chest discomfort can worsen, and fatigue remains prominent.

• By Day 8: Most symptoms ease, but coughing and tiredness may persist for one to two weeks or longer, depending on individual health.

Complications of Influenza

Most people recover from the flu within a few days to two weeks, but some develop serious complications that can be life-threatening or even fatal.

Pneumonia is a severe complication that can be caused by the flu virus alone or by a combination of flu and bacterial infections. When the lungs become inflamed, pus and other fluids fill the alveoli, blocking oxygen from entering the bloodstream. Without enough oxygen, the body’s cells cannot function properly, potentially leading to death.

Other serious complications from the flu include:

• Heart inflammation (myocarditis)

• Brain inflammation (encephalitis)

• Muscle tissue inflammation (myositis, rhabdomyolysis)

• Multi-organ failure (such as respiratory or kidney failure)

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The flu can also trigger an extreme inflammatory response in the body and lead to sepsis, a potentially fatal reaction to infection.

Flu can worsen chronic health conditions. For instance, people with asthma may experience severe asthma attacks, and those with chronic heart conditions may see their symptoms worsen.

High-Risk Groups for Flu Complications

Hospitalizations and deaths from the flu mainly occur among high-risk populations, including:

• Adults aged 65 and older

• Children under 2 years old

• People with asthma

• Those with chronic lung diseases (e.g., COPD, cystic fibrosis)

• Individuals with neurological or neurodevelopmental disorders

• People with blood disorders (e.g., sickle cell disease)

• Those with endocrine disorders (e.g., diabetes)

• Individuals with heart disease (e.g., congenital heart disease, congestive heart failure, coronary artery disease)

• People with kidney or liver disease

• Individuals with metabolic disorders (e.g., genetic or mitochondrial disorders)

• People with a body mass index (BMI) of 40 kg/m² or higher

• People under 19 taking long-term aspirin or salicylate-containing medications

• Individuals with weakened immune systems due to illness (e.g., HIV/AIDS, leukemia) or treatments (e.g., chemotherapy, radiation, long-term steroid use)

• People who have had a stroke

• Individuals with certain disabilities, especially those affecting muscle function, lung function, or the ability to cough, swallow, or clear respiratory fluids

What to Do After Getting the Flu

Most flu cases are mild. Here are three important steps to take:

1. Rest

   You may feel very weak and fatigued until your fever returns to normal (typically about 3 days). Rest helps your body conserve energy to fight the infection.

2. Stay Home

   Avoid work, school, or any places where you might spread the virus, especially while you’re contagious. Adults are usually contagious for 3–5 days after symptoms appear; young children can remain contagious for up to 7 days.

3. Hydrate

   Drink plenty of fluids to replenish what’s lost from fever and sweating. If your urine is dark, you need more water. Try to drink a glass of water every hour while awake.

   
   

If you’re in a high-risk group or experience severe symptoms—such as difficulty breathing, chest pain, sudden dizziness, severe vomiting, or fever with rash—seek medical attention promptly.