Influenza (Flu): Symptoms, Prevention & Treatment

Guide to influenza: transmission, symptoms, high-risk groups, vaccination, and antiviral treatment for disease management.

10 min readLast updated: 2026-02-17

Quick Facts

Prevalence
Infects 1 billion people annually worldwide
Mortality
Causes 290,000-650,000 deaths yearly globally
Prevention
Vaccination is most effective prevention method

What Is Influenza?

Influenza (the flu) is an acute, contagious viral respiratory illness caused by influenza A or B viruses. The virus spreads through respiratory droplets when infected people cough or sneeze. Most people recover within 1-2 weeks, but some develop serious complications, particularly elderly persons and those with underlying medical conditions. Globally, influenza causes significant morbidity and mortality annually.

Key Info
Influenza is different from the common cold. It has a faster onset of systemic symptoms and causes more severe illness in vulnerable populations.

Causes and Risk Factors

Transmission occurs through:

  • Respiratory droplets from coughing or sneezing
  • Direct contact with infected persons
  • Touching contaminated surfaces then touching nose/mouth

High-risk groups for severe illness:

  • Age 65 years and older
  • Pregnancy
  • Chronic medical conditions (heart, lung, kidney disease)
  • Immunosuppression
  • Severe obesity
  • Children under 5 years

Symptoms

Symptoms appear 1-4 days after exposure:

  • Fever and chills
  • Cough (usually dry)
  • Body aches (myalgia)
  • Fatigue and weakness
  • Headache
  • Sore throat (sometimes)
  • Nasal congestion (less common)

Gastrointestinal symptoms occur primarily in children.

Diagnosis

Diagnosis involves:

  • Clinical symptoms and epidemiological context
  • Rapid influenza diagnostic tests
  • RT-PCR (most accurate)
  • Viral culture
  • Serology
Clinical Note
PCR testing is gold standard and detects virus in most symptomatic patients. Testing is most sensitive in first 3-4 days of illness.

Treatment and Management

Supportive care:

  • Rest and hydration
  • Acetaminophen or ibuprofen (not aspirin in children)
  • Cough suppressants

Antiviral therapy (oseltamivir, zanamivir):

  • Most effective if started within 48 hours of symptom onset
  • Reduces symptom duration by 1 day
  • Prevents complications in high-risk patients

Hospitalization for severe cases with pneumonia or organ dysfunction.

Prevention

Primary prevention:

  • Annual influenza vaccination (most effective)
  • Proper hand hygiene
  • Covering mouth when coughing/sneezing
  • Avoiding close contact with ill persons
  • Not touching face after touching contaminated surfaces
Warning
Seek immediate care for severe symptoms including difficulty breathing, chest pain, confusion, severe weakness, or rapid deterioration after initial improvement.

When to See a Doctor

See a doctor if symptoms persist beyond 10 days, worsen after initial improvement, or you're in a high-risk group. Antiviral therapy should start early. Monitor for secondary bacterial pneumonia.

Sources

  1. [1]Petrova VN, Russell CA. "Influenza." Nature Reviews Microbiology, 2018.
  2. [2]CDC Advisory Committee on Immunization Practices. "Prevention and Control of Influenza." MMWR Recommendations and Reports, 2015.

Medically reviewed by

Medical Review Team, Infectious Diseases

Last updated: 2026-02-17Sources: 2

The content on Medical Atlas is for informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider.