Influenza: Symptoms, Treatment and Prevention

Influenza, commonly called the flu, is a contagious respiratory infection caused mainly by influenza A and B viruses. It affects the nose, throat, and sometimes the lungs. Although influenza can circulate throughout the year, cases in Mexico usually increase during the fall and winter.

For many people, the flu causes a short-term illness that improves with rest and supportive care. However, influenza is not simply a severe cold. It can lead to pneumonia, worsen chronic conditions, and require hospitalization—especially in young children, older adults, pregnant women, and people with certain medical conditions.

Recognizing the symptoms and seeking timely medical advice can help determine whether testing or antiviral treatment is needed.

Influenza is a viral infection of the respiratory system. It is not the same as “stomach flu,” a commonly used but inaccurate term for infections that primarily cause vomiting and diarrhea.

Symptoms usually begin between one and four days after exposure, with an average incubation period of about two days. Unlike a common cold, flu symptoms often develop suddenly.

Symptoms vary according to a person’s age, general health, and immune response.

Common signs include:

• Fever or feeling feverish.
• Chills.
• Cough, which is often dry.
• Sore throat.
• Runny or stuffy nose.
• Muscle or body aches.
• Headache.
• Significant fatigue.
• General weakness.
• Reduced appetite.

Not everyone with influenza develops a fever. Children may also experience nausea, vomiting, or diarrhea along with respiratory symptoms.

Influenza, the common cold, and COVID-19 are different respiratory infections, although their symptoms can overlap.

• Symptoms often begin suddenly.
• Fever, chills, and significant body aches are common.
• Fatigue may be intense.
• Complications can develop quickly.

• Symptoms usually develop gradually.
• A stuffy or runny nose and sneezing are more prominent.
• Fever and body aches are less common or milder.
• The illness is usually less severe.

Both COVID-19 and influenza may cause fever, coughing, fatigue, congestion, sore throat, and body aches. It is not always possible to distinguish between them based on symptoms alone.

Testing may be appropriate when the result could affect treatment, when a patient has risk factors for complications, or when symptoms are severe. A person can also have influenza and COVID-19 at the same time.

Influenza spreads mainly through respiratory particles released when an infected person talks, coughs, sneezes, or breathes. Transmission is more likely during close contact and in crowded indoor spaces with limited ventilation.

Less commonly, infection may occur after touching a contaminated object and then touching the eyes, nose, or mouth.

The virus may be detectable approximately one day before symptoms begin and for five to seven days afterward. People are generally most contagious during the first three days of illness. Young children and people with weakened immune systems may remain contagious for longer.

Anyone can develop severe influenza, but the risk is higher among:

• Children younger than 5, especially those younger than 2.
• Adults aged 65 and older.
• Pregnant women.
• People within two weeks after the end of pregnancy.
• Residents of nursing homes or long-term care facilities.
• People with asthma or chronic lung disease.
• Patients with heart disease.
• People with diabetes.
• Patients with kidney or liver disease.
• People with neurological or neuromuscular conditions.
• Patients with weakened immune systems.
• People with severe obesity.
• Children and teenagers receiving long-term aspirin or salicylate therapy.

If you belong to one of these groups and develop flu symptoms, contact a healthcare professional promptly—even if the illness initially appears mild.

Pneumonia is one of the most serious complications of influenza. It may be caused by the virus itself or by a secondary bacterial infection.

Other complications include:

• Dehydration.
• Ear infections in children.
• Sinus infections.
• Asthma attacks.
• Worsening chronic obstructive pulmonary disease.
• Poor diabetes control.
• Worsening heart failure.
• Inflammation of the heart.
• Inflammation of the brain.
• Muscle damage.
• Respiratory failure.
• Sepsis.

A particularly concerning pattern is an initial improvement followed by the return of fever, worsening cough, or difficulty breathing.

A physician will consider your symptoms, how long you have been sick, your medical history, and whether influenza is circulating in the community.

Respiratory testing may be recommended when:

• The patient has an increased risk of complications.
• Symptoms are severe or getting worse.
• Hospitalization is required.
• The result could change treatment decisions.
• Influenza must be distinguished from COVID-19 or another infection.

A negative rapid flu test does not always rule out influenza. Your physician may recommend a more sensitive molecular test or begin treatment based on the clinical assessment.

People with mild influenza and no risk factors can often recover at home with:

• Adequate rest.
• Sufficient fluids.
• Food as tolerated.
• Appropriate medication for fever or pain.
• Careful monitoring for warning signs.

Antibiotics do not treat uncomplicated influenza because they do not work against viruses. They are prescribed only when a physician diagnoses or suspects an additional bacterial infection.

Children and teenagers with influenza should not be given aspirin or medicines containing salicylates because of the risk of Reye syndrome, a rare but serious complication.

Influenza antivirals are prescription medications. They may reduce the duration of symptoms and lower the risk of certain complications.

Treatment provides the greatest benefit when started within 48 hours of symptom onset, but this timeframe is not an absolute cutoff. According to CDC clinical guidance updated in 2026, treatment may still provide benefits when started later in hospitalized patients and people with severe, progressive, or complicated influenza.

Prompt antiviral treatment is especially important for:

• Hospitalized patients.
• People whose symptoms are severe or worsening.
• Patients at increased risk of complications.
• Pregnant or recently postpartum women.
• Young children and older adults with suspected influenza.

When treatment is clearly indicated, it may be started without waiting for laboratory confirmation. The physician will select the appropriate medication according to the patient’s age, pregnancy status, kidney function, medical history, and illness severity.

Annual vaccination is the primary way to reduce the risk of influenza and its complications. Flu vaccines are reviewed and updated regularly to provide protection against the strains expected to circulate during each season.

General recommendations support yearly influenza vaccination beginning at 6 months of age, unless a specific contraindication exists. Mexico’s public vaccination campaigns establish priority groups and guidelines that may change from one season to another.

The influenza vaccine:

• Cannot guarantee that a person will not become infected.
• Can reduce the likelihood of illness.
• Helps lower the risk of hospitalization and complications.
• Does not cause influenza.
• Must be updated each season.

The formulation may be trivalent or quadrivalent depending on the country, season, and health authority. For example, Mexico’s 2025–2026 winter guidelines included a quadrivalent vaccine, while the United States used trivalent formulations.

The number of strains should not be used as the only measure of vaccine quality. The appropriate choice is a vaccine authorized for the current season, age group, and health condition.

In most cases, yes. Current CDC recommendations state that people with egg allergies can receive any age-appropriate influenza vaccine without additional safety measures beyond those recommended for all vaccine recipients.

An egg allergy is different from having experienced a severe allergic reaction to a previous flu vaccine or one of its other components. Anyone with a history of a serious vaccine reaction should speak with a physician before vaccination.

In addition to annual vaccination, these measures can reduce transmission:

• Wash your hands regularly with soap and water.
• Use an alcohol-based hand sanitizer when handwashing is unavailable.
• Avoid touching your eyes, nose, and mouth.
• Cover coughs and sneezes with a tissue or the inside of your elbow.
• Discard used tissues immediately.
• Improve ventilation in indoor spaces.
• Avoid close contact with people who are sick.
• Consider wearing a well-fitting mask in crowded indoor spaces or around vulnerable people.
• Clean frequently touched surfaces.
• Avoid sharing glasses, utensils, or personal items while sick.

If you develop symptoms, stay home and avoid contact with others. You may gradually return to your usual activities after your symptoms have been improving overall and you have been fever-free for at least 24 hours without fever-reducing medication.

For the following five days, take additional precautions such as improving ventilation, practicing careful hand hygiene, wearing a mask, and maintaining distance around people at higher risk.

Arrange a medical assessment promptly if:

• You belong to a high-risk group.
• You are pregnant or recently postpartum.
• Your symptoms are severe.
• Your fever persists or returns.
• Your cough is getting worse.
• You have a chronic medical condition.
• You cannot maintain adequate hydration.
• You initially improve and then become ill again.

Timely medical care allows your physician to determine whether you need testing, antiviral treatment, or monitoring for complications.

Go to the Emergency Department if an adult develops:

• Difficulty breathing or shortness of breath.
• Persistent pain or pressure in the chest or abdomen.
• Persistent dizziness, confusion, or difficulty waking.
• Seizures.
• Little or no urination.
• Severe weakness or muscle pain.
• Blue or gray lips or skin.
• Worsening of a chronic medical condition.
• Fever or cough that improves and then returns or worsens.

Seek emergency care if a child develops:

• Fast or difficult breathing.
• Ribs pulling inward with each breath.
• Blue or gray lips or face.
• Chest pain.
• Dehydration, a dry mouth, no tears, or significantly reduced urination.
• Extreme drowsiness or reduced interaction.
• Seizures.
• Muscle pain so severe that the child refuses to walk.
• Fever or cough that improves and then becomes worse.
• Any fever in an infant younger than 12 weeks.

If you have flu symptoms, belong to a high-risk group, or need guidance about vaccination, schedule an appointment with an Internal Medicine specialist at BlueNetHospitals Los Cabos. Children should be assessed by a Pediatrics specialist.

📲 Schedule an appointment via WhatsApp:
+52 (624) 151 0693

If you have difficulty breathing, chest pain, confusion, seizures, or another emergency warning sign, go directly to the Emergency Department.

📞 BlueNetHospitals Los Cabos Emergency Department:
+52 (624) 104 3911

Yes. Influenza and the flu refer to the same respiratory infection. “Stomach flu” is not influenza and is usually caused by a different virus.

No. Although fever is common, some people with influenza do not develop one, particularly older adults and patients with certain medical conditions.

Most people improve within approximately one week. Coughing, fatigue, and weakness may continue for two weeks or longer.

A person may spread the virus from about one day before symptoms begin until five to seven days afterward. Young children and immunocompromised patients may remain contagious for longer.

No. Antibiotics do not work against viruses. They may be prescribed only when a physician diagnoses or suspects a secondary bacterial infection.

Antivirals require a prescription and work best when started within 48 hours. They may still provide benefits when started later in hospitalized, high-risk, or severely ill patients.

No. Injectable influenza vaccines do not cause influenza. Some people may develop temporary soreness at the injection site, fatigue, or a low-grade fever.

Generally, yes. Egg allergy does not require additional precautions beyond those normally used for vaccination. Consult your physician if you previously had a severe reaction to a flu vaccine.

Yes. It is possible to have both infections simultaneously. Because their symptoms overlap, your physician may recommend specific testing.

Seek emergency care for difficulty breathing, chest pain, confusion, seizures, blue or gray skin, severe dehydration, or symptoms that improve and then return more intensely.