Influenza, commonly known as the flu, is an acute and contagious respiratory infection caused by influenza viruses. It is not just a common cold; it can lead to serious complications, including pneumonia or the worsening of existing health problems. Primarily affecting the respiratory tract (nose, throat, bronchi, and even lungs), the flu usually occurs in seasonal epidemics, impacting millions of people worldwide each year.

Causes and Risk Factors of Influenza

Influenza virus causes the flu. Three main types of influenza viruses affect humans: A, B, and C. Types A and B primarily circulate during the seasonal epidemic. Type A is further classified into subtypes based on the proteins present on its surface. These viruses constantly evolve, necessitating annual vaccine adaptation.

The flu transmits easily from person to person. An infected individual spreads the virus by talking, coughing, or sneezing. Contaminated respiratory droplets can directly reach others’ eyes, nose, or mouth. Contact with contaminated surfaces, followed by touching the face, is also a mode of transmission. Infection is possible even before symptoms appear and up to seven days after their onset, sometimes longer in young children or immunocompromised individuals.

Certain factors increase the risk of severe complications, not necessarily the risk of contracting the disease. Individuals aged 65 and older, young children (especially under 5), pregnant women, and individuals with chronic diseases (heart, lung disease, diabetes, asthma, etc.) are at high risk. Immune suppression, due to diseases or treatments, also makes people more vulnerable.

Symptoms and Signs of Influenza

Flu symptoms often appear abruptly. They can vary from person to person and depending on the type of virus. Here are common signs of the flu:

• High fever (often above 100.4°F / 38°C)
• Chills and sweats
• Severe headaches
• Body aches and widespread muscle pain
• Severe fatigue, weakness, or prostration
• Dry cough
• Sore throat
• Runny nose or nasal congestion
• Sneezing

Vomiting and diarrhea may occur, especially in children. Complications include pneumonia (viral or bacterial), bronchitis, sinusitis, otitis, or exacerbation of chronic diseases such as asthma or heart failure. Symptoms generally last 7 to 10 days, but cough and fatigue can persist for a few weeks.

Diagnosis of Influenza

Flu diagnosis begins with a clinical evaluation. A doctor suspects flu based on described symptoms and the time of year (flu season). Laboratory tests confirm the diagnosis.

Rapid antigen detection tests can identify the presence of the influenza virus. These tests are fast, but their sensitivity varies. They may yield false-negative results. The reference test remains Reverse Transcription Polymerase Chain Reaction (RT-PCR). This test detects the genetic material of the virus and offers high reliability.

Specimens are generally collected via nasopharyngeal swab. Other tests include viral cultures, but their use is declining due to their response time. For complicated cases or epidemiological surveillance, more extensive tests may be necessary.

Treatments and Management of Influenza

Flu management primarily aims to relieve symptoms and prevent complications. Rest is essential for recovery. Sufficient hydration helps combat fever and dehydration.

Medications relieve symptoms. Antipyretics like acetaminophen or ibuprofen lower fever and reduce pain. Decongestants and expectorants can help with respiratory symptoms. Do not use aspirin in children or adolescents with flu, due to the risk of Reye’s syndrome.

In some cases, antivirals are prescribed. These medications, such as oseltamivir (Tamiflu) or zanamivir (Relenza), target the virus. They reduce the duration and severity of the illness. They also decrease the risk of complications. The effectiveness of antivirals is maximal if taken within 48 hours of symptom onset. They benefit individuals at high risk of complications or those with severe flu.

Recent Scientific Advances in Influenza

Influenza research is highly active, seeking more effective solutions. In the first half of 2025, new studies have deepened our understanding and our tools for combating it. Efforts focus on developing universal vaccines, protecting against multiple strains of influenza virus. Clinical trials are underway for vaccine candidates targeting viral proteins conserved across strains, which could make annual vaccination less necessary.

New technological platforms, such as mRNA, continue to develop vaccines more rapidly. Research is exploring broad-spectrum antivirals capable of fighting different viral strains, including those resistant to current treatments. Genomic surveillance of influenza viruses is constantly improving. Rapid sequencing methods allow for the detection of emerging new strains and tracking their spread, thereby facilitating vaccine adaptation and public health responses. These advances aim to strengthen our ability to prevent and treat influenza, reducing its global impact.

Prevention of Influenza

Vaccination remains the most effective way to prevent the flu and its complications. The flu vaccine is updated annually to match the circulating viral strains. Public health authorities recommend the vaccine for individuals at high risk of complications. The ideal time for vaccination is before the start of the flu season.

Hygiene measures also contribute to prevention:

• Wash your hands frequently. Use soap and water, or an alcohol-based hand sanitizer.
• Cover your mouth and nose when coughing or sneezing. Use a disposable tissue or the crook of your elbow.
• Avoid touching your face (eyes, nose, mouth).
• Stay home if you are sick. This prevents the spread of the virus to others.
• Avoid close contact with sick people.
• Regularly ventilate enclosed spaces to reduce the concentration of viruses in the air.

Living with Influenza

Living with the flu involves managing symptoms and promoting quick recovery. When the flu strikes, rest is paramount. Your body needs energy to fight the infection. Hydrate extensively by drinking water, fruit juices, or broths. This prevents dehydration, especially in case of fever.

Follow your doctor’s advice regarding medications to relieve fever and pain. Avoid alcohol and tobacco, as they can further irritate the respiratory tract and prolong convalescence. If symptoms worsen or new problems appear, consult a healthcare professional immediately. Full recovery can take several weeks, even after acute symptoms disappear. Plan for a gradual return to your usual activities.

Frequently Asked Questions (FAQ)

Can the flu be transmitted before symptoms appear?

Yes, a person can transmit the influenza virus one day before symptoms appear and up to five to seven days after. Young children and immunocompromised individuals may remain contagious longer.

What is the difference between the flu and a common cold?

The flu manifests more suddenly and intensely than a cold. It causes high fever, severe muscle aches, and extreme fatigue. A cold generates milder symptoms, mainly nasal and throat-related.

Should I take antibiotics for the flu?

No, antibiotics do not act on viruses. They are ineffective against the flu. A doctor prescribes antibiotics only in case of bacterial complications, such as bacterial pneumonia.

When should I see a doctor for the flu?

See a doctor if you are in a high-risk group for complications (elderly, young children, pregnant women, people with chronic diseases). Also consult if you experience severe or persistent symptoms, such as breathing difficulties, chest pain, dizziness, or a sudden worsening of symptoms.

Is the flu vaccine safe?

Yes, the flu vaccine is safe and effective. Common side effects are mild and short-lived: pain, redness or swelling at the injection site, mild fever, or muscle aches. Serious allergic reactions are rare.

Additional Resources

• World Health Organization (WHO)

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