Skip to content

Influenza is an inflammation of the respiratory tract caused by the influenza viruses. Unlike with common colds, there is a vaccine against influenza. Influenza viruses are divided into types A, B and C. Types A and B usually cause epidemics.

Influenza is transmitted through droplet transmission, casual contact and the airborne route.  The incubation period varies from 1 to 7 days but is usually 2 to 3 days. Contagiousness is highest during the first 3 to 4 days of symptoms appearing and lasts for about a week. However, the infected person can pass on the virus just 1 to 2 days before experiencing clear symptoms.

Seasonal influenza occurs in 5% to 15% of adults and 15% to 30% of children. The main symptoms usually last for 3 to 8 days. The most common complications in adults include pneumonia, sinusitis and worsening of asthma and other pulmonary conditions. 

Seasonal influenza epidemics occur every winter. They usually start around New Year and last for 2 to 3 months. Influenza should be suspected only during an influenza epidemic. It’s good to remember that even during an influenza epidemic over half of respiratory infections are common colds. During an epidemic, influenza can be diagnosed from its symptoms, which include sudden fever and dry, barking cough.


  • The most common symptoms are sudden fever (in adults, 38°C or more), sore throat, cough and a runny nose. 
  • Other symptoms may include pain in the extremities, headache, shivering and fatigue. 
  • Vomiting and diarrhoea may occur. 

A mild rise in body temperature and a runny nose as the main symptoms are not typical of influenza. For the majority of patients, home care is enough. During the influenza season, your health status can be assessed on the phone. If necessary, the nurse can authorise sick leave of up to three days. If you’re ill, you should not go to your study site until you’ve had one fever-free day. 


  • Rest and drink plenty of fluids.
  • Lower your temperature with painkillers (e.g. paracetamol 0.5 g to 1 g three times daily or ibuprofen 400 mg to 800 mg three times daily). This also alleviates muscle pain.
  • Influenza often gets better on its own after a week’s rest.

If you know you have some underlying condition and you belong to a risk group (linkki THL:n sivuille), contact a healthcare professional for assessment of the need for further treatment. 

When should you seek treatment?

Contact a healthcare professional immediately if:  

  • Your general health is impaired or you have symptoms indicative of pneumonia (shortness of breath, chest pain, no energy to move). 
  • You experience sudden dizziness or confusion. 
  • You experience severe or continuous vomiting. 
  • Your fever returns or your condition worsens after the symptoms had already started to improve. 


Even during an epidemic, it is worth being vaccinated. Vaccination reduces the risk of getting influenza by about 80% if the cause of the epidemic is one of the virus types in the vaccine. 

Vaccine protection is acquired within about two weeks. If the vaccinated person has already contracted an influenza virus, the vaccine can no longer prevent influenza. However, in this case vaccination is not harmful. Vaccination is unlikely to cause more severe influenza.

Protecting yourself from infection 

The best way to protect yourself from any respiratory infection is to ensure good hand hygiene, to cover your nose and mouth when coughing, and to use a disposable tissue when sneezing. When you’re ill, it’s best to avoid other people.

Information sources: The Finnish Medical Society Duodecim: Terveysportti, Lääkärin tietokanta database

FSHS General Practitioner / 12 September 2019 

Service options