The flu vaccine as prevention

When you are vaccinated for the flu, inactivated flu viruses or parts of the virus are injected into a muscle or under the skin. A nasal spray containing weakened (attenuated) flu viruses is also available for children over the age of two years and teenagers who already have certain other medical conditions.

After it comes into contact with the vaccine, our immune system starts to produce antibodies to fight the virus. Then, if an active virus comes along that is the same as the one introduced by the vaccine, the body recognizes it and can fight it off.

However, flu viruses are constantly changing (mutating), and entirely new strains of the virus also emerge. So the flu vaccine does not provide long-term protection. If you want to have protection during the flu season, you need to have a different vaccination every year.

The flu vaccine is adjusted each year to target the virus strains expected in the next season. But it takes time to produce these flu vaccines. That is why the vaccine is made before we known for certain which flu viruses will be circulating during the season. Most of the time, these predictions are accurate enough to develop a suitable vaccine, though.

After having a flu shot, it takes about 14 days for your body to produce enough antibodies to fight off a flu infection if you become infected. This means that if vaccination is to protect a person during the whole flu season, they should be vaccinated before the first cases of influenza arise. So in Europe, fall is the best time to get a flu shot. But because flu outbreaks can also occur in January, February or even later, it might still be worth getting vaccinated later.

Research has shown the following: Vaccination is more effective when the vaccine matches the virus strains circulating that year. But that doesn't work out equally well every year. For example, the viruses can change over the course of a flu season, with the vaccine possibly becoming less effective

It is estimated that vaccination can reduce the risk of infection among healthy adults by up to 60 percent. This depends on various factors, such as whether someone had the flu or got a flu shot in previous years, or their age. The prevalence of flu viruses during a flu season also plays a role. The more flu viruses there are, the higher the risk of infection. But that also means that more people will be able to benefit from the vaccine.

The figures in the table below may help make this clearer. But how much the vaccine will help can never be precisely predicted for each year or for a new virus.

The German Standing Immunization Committee (STIKO) of the Robert Koch Institute is responsible for vaccine recommendations in Germany. It recommends annual vaccinations for people who have a higher risk of flu complications. They include:

• People over the age of 60
• People with chronic medical conditions like asthma or COPD, cardiovascular disease, diabetes, liver or kidney disease, multiple sclerosis or HIV
• Pregnant women starting in the second trimester, and starting in the first trimester of pregnancy if there is an increased health risk due to an existing condition
• People whose jobs involve a lot of contact with the public
• People who live with others who have a greater risk of complications from the flu

This recommendation also applies to:

• Anyone who cares for children, older people or sick people (such as people who work in nursing homes, doctors' offices, hospitals or daycare centers).
• People whose jobs involve a lot of contact with the public.

STIKO recommends vaccination for these individuals for two reasons: These people are very often exposed to the viruses. And they can easily infect others who are more likely to have serious complications if they get the flu.

A flu vaccination may cause some temporary side effects, such as fever, tiredness, headache, muscle pain or joint pain. But these side effects usually pass within one or two days.

If the vaccine is given as an injection, there could be temporary mild pain, redness or swelling where the needle was inserted.

Vaccination using nasal spray may lead to a temporary stuffy or runny nose, cough, or sore throat. Children and teenagers who have severe asthma or a weakened immune system should not be vaccinated with a nasal spray.

STIKO recommends that people aged 60 and older receive a high-dose vaccine or an MF-59-adjuvanted vaccine. Both vaccines are expected to provide slightly better protection against the flu for older adults than the "regular" flu vaccine.

The reason for this is that our immune system becomes less effective as we get older. That is why the vaccine may be less effective in older people than in younger people. The high-dose vaccine and the MF-59-adjuvanted vaccine are slightly more effective and are intended to compensate for this.

In addition to the annual flu shot in the fall, some people are also advised to get a COVID-19 vaccine – for instance, older adults aged 60 and older or people who live in retirement or nursing homes. COVID-19 vaccines can reduce the risk of becoming seriously ill from COVID-19.

Vaccination against RSV is also recommended for people aged 60 and older who have certain serious medical conditions or who live in nursing homes, as well as for people aged 75 and older. RSV is a virus that causes infections of the airways. The infection can lead to pneumonia, particularly in older adults and people with certain underlying medical conditions.

You can get vaccinated against the flu, COVID-19 and RSV at the same time – all at one appointment.

The Robert Koch Institute has listed answers to frequently asked questions about the flu vaccine on its website (in German). You will also find information there about who is not eligible for vaccination.