Acute Respiratory Viral Infection Characteristics

Acute respiratory viral infections, notably influenza, exhibit sudden high fever, headache, muscle aches, and fatigue. Influenza is a major infectious disease, causing global pandemics with widespread outbreaks across almost every continent, resulting in millions of illnesses and deaths.


Influenza viruses spread through respiratory droplets when an infected person coughs, sneezes, or talks. The virus can also spread by touching surfaces contaminated with the virus and then touching the nose or mouth. Dense populations, like in schools or factories, facilitate rapid transmission.

Incubation Period

The incubation period for influenza is about 1-3 days.


Symptoms begin 1-3 days after exposure and include high fever, runny nose, headache, chills, muscle aches, and severe fatigue. Additional symptoms may include nasal congestion and sore throat. Prolonged illness may lead to bronchitis and persistent cough. The disease is more severe and lasts longer than a common cold, typically resolving in 5-7 days, but severe cases can lead to complications like pneumonia or encephalitis, which can be fatal. High-risk groups include:

  • Individuals aged 65 and older
  • Children under 2 years old
  • People with chronic diseases (lung, heart, kidney, diabetes, immunodeficiency)
  • Obese individuals
  • Pregnant women in their second or third trimester during influenza season

Most cases are treated symptomatically. If influenza is suspected, consult a physician.

  • Avoid contact with infected individuals.
  • Wash hands frequently.
  • Wear a mask when ill.
  • Avoid crowded places.

Flu vaccination is crucial, especially for high-risk groups, to prevent severe complications.

Who Should Receive the Flu Vaccine
  • Children aged 6 months to 2 years
  • Pregnant women (from 4 months gestation)
  • Elderly (65 years and older)
  • Individuals with chronic diseases (COPD, asthma, heart disease, stroke, kidney failure, diabetes, cancer patients undergoing chemotherapy)
  • Individuals with brain disabilities who cannot care for themselves
  • People with compromised immune systems, thalassemia patients, and symptomatic HIV patients
  • Obese individuals (weight over 100 kg or BMI > 35)
  • Healthcare workers exposed to influenza
When to Get Vaccinated

The flu vaccine can be administered year-round but is best given before the rainy season (May) and winter (October) due to the onset of outbreaks. Pregnant women are at a higher risk and should receive one flu shot from 4 months gestation to provide immunity for themselves and their unborn child.

Vaccine Dosage
  • Individuals aged 9 years and older: 1 dose
  • Children under 9 years old who have never received a flu vaccine: 2 doses in the first year (4 weeks apart), then 1 dose annually thereafter.
Contraindications for Flu Vaccination
  • Severe allergy to egg protein
  • Severe allergic reaction to a previous flu vaccine or its components
  • Current acute illness or fever
  • Recently recovered from acute illness (within 7 days)
  • Recent hospital discharge (within 14 days)
  • Uncontrolled chronic diseases (e.g., chest pain, palpitations, shortness of breath)
  • High-risk pregnancy complications (e.g., toxic goiter, pre-eclampsia)
Severe Allergic Reactions

Severe reactions include difficulty breathing, hoarseness, hives, pallor, weakness, rapid heartbeat, or dizziness.


Information Source : Department of Disease Control, Ministry of Public Health