What is the Flu?

The flu is a contagious respiratory illness caused by Influenza viruses. It can infect the nose, throat, and sometimes the lungs. Symptoms can be mild to severe, and it can also lead to death if the virus triggers severe inflammation in the lungs. Although avoiding close contact with people who are sick, staying home when you are sick, covering your mouth and nose with a tissue when coughing or sneezing and washing your hands often to protect you from germs, may help to prevent getting the flu. Medical experts agree that getting a flu shot, or flu vaccine, is the single most effective way to protect us and others from the illness.

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How does the flu spread?

Seasonal flu spreads easily, especially in crowded areas including schools and nursing homes. When an infected person coughs or sneezes, droplets containing viruses (infectious droplets) are dispersed into the air. Droplets can spread up to one meter and can infect people who breathe them in, standing near. The virus can also be spread by hands contaminated with influenza viruses.

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Which people are at the highest risk from the flu?

Anyone can get the flu. Even healthy people at any age can develop serious complications related to the flu, but some people are at higher risk, like people 65 years and older, people with certain chronic medical conditions (such as asthma, diabetes, or heart disease), pregnant women and small children under 5 years of age.2

What are the complications of the flu?

For most people, the flu only lasts from several days to two weeks. Others may develop serious complications that can be even life-threatening.4 Some of the flu complications may include:

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What are the flu symptoms?

Flu symptoms can be mild to severe and at times can lead to death if the virus triggers severe inflammation in the lungs. Flu symptoms usually come on suddenly. People who have the flu often feel some or all of these symptoms:6



Shortness of breath

Sore throat


Runny or stuffy nose

Fatigue (tiredness)

Muscle or body ache


What is a typical flu pattern?

Phase 1
(days 1–3)

Although not everyone with the flu will have a fever, sudden appearance of fever is very common, headache, muscle pain, weakness, dry cough, sore throat and sometimes a stuffy nose.7

Phase 2
(day 4)

Fever and muscle aches decrease. Dry, sore, and hoarse throat, cough and mild chest discomfort may be present accompanied by feeling tired.7

Phase 3
(day 8)

Symptoms gradually disappear but cough and feeling tired may last for few more weeks.7

When to ask for medical help?

Ask for immediate medical assistance if you are in the high risk group or if you have any concerns related to any of the following symptoms:

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How to protect others?

The best way to protect others is to stay at home especially while being contagious.8


Symtom onset Gradual Abrupt
Fever Rare Usual
Aches Slight Usual
Chills Uncommon Fairly common
Fatigue, weakness Sometimes Usual
Sneezing Common Sometimes
Chest discomfort, cough Mild to moderate Common
Stuffy nose Common Sometimes
Sore throat Common Sometimes
Headache Rare Common

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

The flu and common cold are both contagious respiratory illnesses but are caused by different viruses. Although symptoms are similar, the flu is caused by influenza viruses, and cold can be caused by several different viruses. Due to similar symptoms, sometimes it can be difficult to differentiate the two. Flu symptoms usually appear more sudden and are more intense; the flu can also have serious complications.

Special tests can tell if a person has the flu or a common cold.9

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How to prevent the Flu?

Getting a flu vaccine is the most important step in preventing a seasonal flu. Flu vaccine reduces flu related illnesses and the risk of developing serious flu complications, the possibility of hospitalizations or death from the flu.11

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What are the key facts about flu vaccination?

World Health Organization (WHO) every year recommends 3 or 4 strains of the virus to be included in the development of the flu vaccines, predicting to be the most common strains for each hemisphere for the flu season.12

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