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While a cold usually develops gradually and causes milder symptoms, flu typically comes on suddenly. Common symptoms include a high fever, chills, headaches, muscle and joint pain, a dry cough, pronounced fatigue and exhaustion. Acute symptoms usually last several days, but tiredness and reduced energy levels may persist for longer.

Flu can be particularly serious for older adults, pregnant women, young children, people with chronic conditions and those with weakened immune systems. Possible complications include pneumonia, inflammation of the heart muscle and a worsening of existing medical conditions.

“Flu can leave even an otherwise healthy person unable to go about their daily life for several days. In older adults and people with chronic conditions, it can also lead to serious complications. Vaccination prepares the immune system to recognise and respond to the virus. If an infection does occur, the body can usually respond more quickly, reducing the risk of severe illness,” says Dr Barbora Kolářová, Head of Outpatient Care and General Practitioner at MY CLINIC.

Book your flu vaccination

At MY CLINIC, we use the Vaxigrip vaccine

Vaxigrip is a trivalent, inactivated vaccine against seasonal flu. It is suitable for adults and children aged six months and older.

It contains inactivated, split components of three selected influenza viruses. These cannot multiply in the human body, so the vaccine cannot cause flu.

The vaccine’s composition is regularly updated in line with World Health Organization recommendations and the influenza viruses expected to circulate during the coming season.

How does the vaccine work?

The vaccine introduces the immune system to characteristic components of influenza viruses, particularly a surface protein called haemagglutinin. The body responds by producing antibodies and developing immune memory.

If a vaccinated person later encounters an influenza virus, their immune system can recognise it and begin responding more quickly. The antibodies make it harder for the virus to attach to cells in the respiratory tract and spread further through the body.

Protection does not develop immediately. The immune system needs approximately two to three weeks, so it is best not to wait until flu is already spreading widely before getting vaccinated.

Why is Vaxigrip trivalent?

Previously used quadrivalent vaccines also contained a component targeting the B/Yamagata influenza lineage. However, global surveillance indicates that this lineage has not been actively circulating since March 2020. International and European health authorities therefore recommended removing it.

The current trivalent vaccine protects against two influenza A subtypes and one influenza B lineage considered relevant for the season. The move to a trivalent formulation therefore reflects the current epidemiological situation rather than a weakening of the vaccine.

What does the research show?

Vaccine effectiveness can vary from one season to another. It depends primarily on how closely the vaccine matches the viruses circulating, as well as the vaccinated person’s age, health and immune response.

A pooled analysis of 165 studies published in 2025 estimated that vaccination was associated with an average 42% reduction in the risk of hospitalisation due to laboratory-confirmed flu. Results varied between seasons and patient groups, and the authors also highlighted limited certainty in some of the available evidence.

Vaccination does not provide complete protection against infection. However, an important benefit is a reduced risk of severe illness, complications and hospitalisation.

Frequently asked questions

1. Can the Vaxigrip vaccine cause flu?
No. Vaxigrip is an inactivated vaccine. It does not contain a virus capable of multiplying and therefore cannot cause flu.

2. Can I still get flu after vaccination?
Yes. No vaccine offers complete protection. Infection can also occur shortly before vaccination or before a sufficient immune response has developed. However, vaccination reduces the likelihood of illness and, above all, the risk of severe illness and complications.

3. How long does protection take to develop, and why is vaccination repeated every year?
Protection develops approximately two to three weeks after vaccination. Annual vaccination is recommended because influenza viruses change and the immunity acquired gradually wanes.

4. Who is Vaxigrip suitable for?
Vaxigrip is suitable for adults and children aged six months and older. It can also be used at any stage of pregnancy and during breastfeeding.
Children under nine who have not previously been vaccinated against flu may need two doses at least four weeks apart. Their paediatrician will determine the appropriate vaccination schedule.

5. What side effects can occur, and when should vaccination be postponed?
The most common reactions are pain, tenderness, redness or mild swelling at the injection site. Temporary tiredness, headaches, muscle aches or a mild fever may also occur. These reactions usually resolve within a few days.

If you have an acute illness with a fever, vaccination is usually postponed until you have recovered. Before vaccination, tell your doctor about any severe allergies, unusual reactions to previous vaccinations, bleeding disorders or treatment that affects your immune system. Your doctor will assess whether vaccination is suitable for you.

Flu is not a cold. Get vaccinated Flu is a highly contagious viral infection of the respiratory tract that affects 10.22.2026