In most cases influenza is a benign illness but for elderly people, pregnant women and people with chronic diseases, the complications of flu can be dangerous. Vaccination remains the best way of preventing the complications of flu and hospitalisation.


Influenza is a very contagious disease in which the virus is transmitted through the airways and can survive for a long time on the hands.

By complying with the simple procedures which protect you from the virus, you will also protect others!

Avoid contact

  • When you have influenza stay at home and try to spare those close to you.
  • As far as possible avoid contact with infected people and their secretions.


  • Wash your hands after sneezing, coughing, after having had contact with a sick person or after using public transport.
  • Cean things which have been in contact with a sick person.

Watch secretions

  • Sneeze into a disposable tissue or into the crook of your arm; this is always better than into your hands which are the most important vector for the transmission of these viruses.
  • Cough, spit and blow your nose into a disposable tissue.


Vaccination remains the best way for people at risk to avoid the complications related to influenza and the risks of hospitalisation.

However, its efficacy can never be guaranteed. It depends in particular on the viruses in circulation, which are subject to constant mutation, and the state of the immune system of the individual concerned.

Whether vaccinated or not, proper hygiene is essential.

Vaccines summed up in 6 questions

1 — Who can be vaccinated?

Everybody can be vaccinated against influenza starting from the age of 6 months. However, vaccination is particularly recommended for:

Group 1: people at risk of complications

  • Pregnant women, from the second trimester
  • Persons with chronic illnesses (of pulmonary origin including severe asthma, heart except high blood pressure, liver, kidney, metabolic including diabetes, neuromuscular or immune system disorders)
  • People aged 65 and over
  • People in institutions
  • Children over 6 months with chronic diseases or on longterm aspirin therapy

Group 2: healthcare workers

Group 3: people living in the same household as

  • People of group 1
  • Children younger than 6 months

Due to the financial cost of sickleave during seasonal epidemics, some companies offer vaccination to their employees.

2 – What is the best time to be vaccinated?

Vaccination takes place in Autumn, preferably at the beginning of the influenza season, from October to December in the Northern hemisphere.

A vaccination is effective after 2 weeks and protects against influenza for at least 6 months.

Because of the mutations which can occur, the vaccine may differ in composition from one year to the next. Vaccines must therefore be renewed every year.

3 – What must I do to be vaccinated?

To be vaccinated, consult your general practitioner even if an epidemic has already been announced.

The doctor will give you a prescription with which you can buy the vaccine at the pharmacy.  Keep the vaccine in the refrigerator and only take it out when you are returning to the doctor.

4 – How does the vaccine work?
The classical vaccine is prepared from inactive viral strains of influenza and is without additives. Once it is injected into the body, the immune system will respond to the intrusion by producing antibodies which will protect the body against infection. The vaccine becomes effective after 2 weeks on average, the time necessary for the production of the antibodies.

5 – Who designs the composition of the vaccines?

A committee of the World Health Organization (WHO) meets twice a year to determine the composition of the vaccine for the coming season. For the Northern hemisphere the meeting takes place in February. Thanks to information provided by the Global Influenza Surveillance Network, which is made up of 142 national influenza centres (among which Sciensano) located in 112 countries throughout the world, the WHO identifies and characterises the strains responsible for the epidemic of the preceding year and tries to anticipate those that will appear in the current year.

The trivalent vaccine is always composed of 3 strains:

  • an A (H3N2) virus
  • an A (H1N1) virus
  • a B virus.

6 – Why be vaccinated?

The flu vaccine is sometimes criticised because its effectiveness is partial and varies from year to year because of the constant mutation of influenza viruses.

However, each year the composition of the vaccine is adapted according to the strains that have been in circulation and are the most likely to cause an epidemic.

Vaccination is always recommended for people at risk and those in contact with them. You get vaccinated to protect yourself and to protect others.

Sciensano coordinates a network of general practitioners and hospitals to ensure the permanent surveillance of influenza activity, of the intensity and severity of epidemics and the impact on the population. Sciensano is also the National Reference Centre (NRC) for influenza virus. The Belgian Official Medicines Control Laboratory (OMCL) of Sciensano, together with the European OMCL network, is responsible for the quality control of the influenza vaccine prior to marketing.

Other sources of information

There are currently no external links associated to this health topic

In the media

QR code

QR code for this page URL