You were near a coughing colleague and are now counting the days. Or you woke up with aches and are wondering where this came from. Let's break down the timeline of flu by stages.
What the flu incubation period is and how long it lasts
This is the time from infection to the first symptoms. With flu it is short: symptoms appear on day 1–4 after infection.
In most people the illness develops quickly, within a few hours. A sharp rise in temperature, aches, and a dry cough are the typical picture. With a cold, symptoms build up gradually over 1–2 days, whereas with flu they develop over a few hours. Flu is usually characterized by fever, aches, and severe weakness, whereas with a cold fever is rare. In children, this is accompanied by ear pain, red eyes, enlarged glands, and reduced activity; they have vomiting and diarrhea more often than adults.
When contagiousness begins and how long a person is contagious
Flu is highly contagious. The virus is transmitted in droplets when coughing, sneezing, and talking.
It is easiest to infect others in the first 5 days after infection. A sick person is most contagious on day 3–4 from the onset of symptoms.
The virus remains alive on hands and surfaces for up to 24 hours. Infection through objects occurs less often: if you touch a surface with the virus and then touch your mouth, nose, or eyes.
How many days fever lasts with flu
Flu symptoms come on suddenly. High temperature is one of the first signs, along with chills and body aches. The exact duration of fever is not specified in the sources, but in most people symptoms resolve within a week without medical help. With flu, fever is usually present; with a cold it is rare. If there is no improvement after 7 days, a doctor is needed.
How long influenza A lasts and when symptoms resolve
Influenza A viruses are the most common cause of seasonal flu. There are no separate timeframes specifically for type A.
A cough may last two or more weeks. The recovery period takes 7–15 days.
What the course of the illness depends on
In some people flu is severe. The risk group includes adults aged 65 and older, pregnant women, and children under 5 years.
The risk is higher with chronic diseases: asthma, diabetes, heart disease. Also with a weakened immune system.
Flu can cause complications: bronchitis, pneumonia, inflammation of the heart, brain, or muscles. It can exacerbate chronic diseases. Sometimes gastroenteritis is called "stomach flu," but it is not flu.
- Age 65 and older
- Pregnancy or recent childbirth
- Children under 5 years
- Chronic diseases of the heart, lungs, kidneys, diabetes
- Weakened immune system
When to see a doctor for flu
The doctor asks about symptoms and, if necessary, orders a test. A swab is taken from the nose or the back of the throat. A rapid test gives a result in 15–20 minutes, but it is less accurate than other tests, whose result can be obtained in an hour or several hours.
You should see a doctor if you are in a risk group or feel very unwell. Also if shortness of breath appears or symptoms do not resolve within 7 days.
Having flu itself is not a reason to call an ambulance. Call 103 or 112 for sudden chest pain, severe difficulty breathing — when a person is gasping and cannot speak — or for a cough with blood.
This material is for reference and does not replace a doctor's consultation.
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This content is for reference and does not replace a doctor's consultation. Medical disclaimer