Unlike many other vaccinations, flu vaccination is recommended annually. One reason for this is that influenza viruses continually change, and the circulating virus variants can differ from season to season. The composition of the vaccines is therefore regularly updated.

What is the seasonal flu vaccine?

The influenza vaccine, also known as the flu vaccine, is designed to protect against the influenza viruses expected to play a significant role in the coming flu season. The virus variants included in the vaccine are selected based on worldwide surveillance data. For the 2026/27 flu season, the recommended vaccines contain components targeting three virus variants: two influenza A viruses (A(H1N1) and A(H3N2)) and one influenza B virus (B(Victoria)). Previous flu vaccines also contained a fourth component targeting the influenza B Yamagata lineage. As viruses belonging to this lineage have not been detected globally to any significant extent since March 2020, the WHO recommends removing this component.

Four inactivated flu vaccines are available in Switzerland in 2026. Three are standard-dose vaccines that can be used from six months of age. The fourth is a high-dose vaccine for older adults; the Federal Office of Public Health (FOPH) recommends using it preferentially for people aged 75 and over and for people aged 65 and over with an additional risk factor.

All four vaccines are injected into a muscle, usually in the upper arm. Inactivated vaccines contain no viruses capable of replicating and therefore cannot cause flu themselves. We are happy to discuss which vaccine is suitable for you during a personal consultation.

A brief history of flu vaccination

In the 1930s, researchers successfully isolated influenza viruses from humans for the first time. This confirmed that flu is caused by viruses rather than bacteria.

The development of the flu vaccine

The development of an influenza vaccine was driven in particular by the US Army. During the First World War, flu had claimed the lives of many soldiers. Living in close quarters in barracks and military camps also encouraged the spread of infectious diseases.

Fertilised hen’s eggs were used to produce the first flu vaccines. This method remains the basis for the production of many flu vaccines today.

The influenza B virus was discovered in 1940. A few years later, a vaccine was developed that protected against both influenza A and influenza B viruses. In 1942, a flu vaccine of this kind was approved for civilian use in the United States for the first time.

How influenza viruses change

During the flu epidemic of 1947, researchers discovered that the antigenic properties of influenza viruses can change, reducing the effectiveness of existing vaccines.

Antigens are distinctive structural proteins on the surface of a virus that are recognised by the immune system. Following vaccination, the immune system produces matching antibodies, among other responses. If the surface structures of influenza viruses change, existing antibodies may be less effective at recognising the altered virus variants. This phenomenon is known as antigenic drift.

Less frequently, a sudden major change occurs, known as antigenic shift. This produces a new influenza subtype against which the population has little immunity. Such viruses can cause pandemics, as most recently occurred in 2009 with “swine flu”. The annual updating of vaccines, however, is a response to ongoing antigenic drift.

Surveillance of influenza viruses

In 1952, the World Health Organization (WHO) established a global network to monitor influenza viruses. Initially called the Global Influenza Surveillance Network (GISN), it was renamed the Global Influenza Surveillance and Response System (GISRS) in 2011. It continues to monitor the evolution of influenza viruses.

The network monitors seasonal influenza viruses as well as newly emerging zoonotic viruses and viruses with pandemic potential. Among other things, the data collected worldwide help identify changes in the viruses at an early stage and inform regular updates to the composition of seasonal flu vaccines.

Who should get vaccinated against seasonal flu?

Flu vaccination is possible from six months of age. It is particularly recommended for people at increased risk of complications from flu. These include:

• People aged 65 and over
• Pregnant women and women up to four weeks after giving birth
• People aged six months and over with certain chronic conditions or a weakened immune system. These include heart and lung conditions (such as asthma), diabetes, severe obesity (BMI of 40 or above), liver and kidney conditions, certain neurological conditions (such as Parkinson’s disease), an absent or poorly functioning spleen, and immune deficiency, for example due to cancer, HIV infection or immunosuppressive treatment
• Certain children born prematurely, during their first two winters after birth
• Residents of nursing homes and facilities for people with chronic conditions

Flu vaccination is also recommended for people who regularly have close contact with individuals at increased risk of complications or with infants under six months of age. These include, in particular, healthcare and nursing professionals and staff working in care facilities. The recommendation also applies to people who have regular or occupational contact with poultry or wild birds.

People who do not belong to these groups can also get vaccinated against seasonal flu if they wish to reduce their personal risk of developing flu.

Infants under six months of age cannot yet be vaccinated against influenza. Following a severe allergic reaction to a flu vaccine or one of its components, a doctor should assess which vaccine is suitable before another vaccination is given.

When is the best time to get vaccinated?

The FOPH recommends getting vaccinated between mid-October and the start of the flu epidemic. Protection develops within approximately two weeks of vaccination and decreases again after a few months. Vaccination in November or early December is usually still timely. For comparison, in the 2024/25 season, the flu epidemic began in mid-December and peaked at the end of January.

Two National Vaccination Weeks will also take place in 2026: from 2 to 7 November and from 23 to 28 November. During these weeks, many medical practices and pharmacies offer vaccinations against flu, Covid-19 and RSV.

The flu vaccine can be given at the same time as, before or after a Covid-19 vaccination.

Children aged six months to eight years who are being vaccinated against flu for the first time receive two doses four weeks apart. For everyone else, one dose per season is sufficient.

How effective is the flu vaccine?

Flu vaccination does not provide complete protection against flu. Its effectiveness depends, among other things, on which influenza viruses are circulating in a given season and how closely they match the virus variants included in the vaccine. The vaccinated person’s age and health also play a role.

It is therefore possible to develop flu despite being vaccinated. However, studies show that illness is often milder in vaccinated people and that severe complications occur less frequently.

Additional benefits of flu vaccination

Flu can place an additional burden on existing chronic conditions. In people with cardiovascular disease, flu vaccination is associated with a lower risk of major cardiovascular events. In people with chronic lung conditions, it can also reduce the risk of flu-related deterioration and associated hospital admissions.

Flu vaccination is also recommended during pregnancy. It not only protects the pregnant woman against flu and possible complications but can also protect the baby during the first few months of life.

Antibodies produced during pregnancy can pass through the placenta to the unborn child. This is particularly important because infants cannot receive their own influenza vaccination until they are six months old.

What side effects are possible?

Flu vaccines have been used for decades and are generally well tolerated. According to the FOPH, up to 25% of vaccinated people experience brief pain or redness at the injection site. Around 5% temporarily develop a raised temperature, muscle aches or a mild feeling of being unwell.

Severe side effects, such as a serious allergic reaction, are very rare. Before vaccination, tell the healthcare professional if you have allergies or have previously had a severe reaction to a vaccine. Vaccination is generally postponed during an acute illness with fever.

Insurance coverage

Since 1 January 2026, vaccinations covered by compulsory basic health insurance have been exempt from the deductible. For flu vaccination, this applies to people aged 65 and over and certain people at increased risk of complications, among others. The 10% co-payment still applies.

For people who do not meet the criteria for coverage, basic health insurance generally does not cover the cost of flu vaccination.

Important: Basic health insurance only covers the administration of the vaccine in medical practices and hospitals. People who get vaccinated at a pharmacy without a doctor’s prescription pay for the vaccination themselves. If vaccination is recommended for occupational reasons, employers generally cover the cost.

Why flu vaccination remains important

Seasonal flu is not a harmless cold. Typical symptoms include the sudden onset of a high fever (above 38°C), chills, coughing, a sore throat and pain when swallowing. In Switzerland, it leads to an estimated 112,000 to 275,000 medical consultations, several thousand hospital admissions and several hundred deaths every year.

People at increased risk of complications are particularly vulnerable.

Annual flu vaccination is an important measure for reducing the personal risk of flu and severe complications and for protecting particularly vulnerable people in your own community.

Alongside vaccination, simple measures help prevent infections: washing your hands regularly, coughing or sneezing into the crook of your elbow, and staying at home if you have flu symptoms.

Resources

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