Flu (influenza)

Many people talk about the flu when they have a common cold. However, these two infections develop differently. While a cold develops slowly, the flu begins quickly and fiercely. 

At a glance

  • Typical flu symptoms are headaches, sore throat, chills, high temperature, and muscle and joint pain throughout the whole body.
  • Flu is caused by being infected by viruses.
  • Many people talk about having flu when they actually have a common cold. However, these two infections develop differently.
  • While a cold develops slowly, people suddenly feel very unwell when they catch flu.
  • Regular hand washing can prevent an infection. A flu vaccination is also available.

Note: The information in this article cannot and should not replace a medical consultation and must not be used for self-diagnosis or treatment.

A young woman blowing her nose

What is flu?

When a common cold emerges, many people talk about the flu, but the two illnesses progress in very different ways. A cold can be distinguished from the flu through their typical ill effects.

Colds occur far more frequently than the flu. But the main difference is that a cold develops slowly, whereas the flu begins quickly and fiercely, including in people who are usually healthy. This means that flu causes people to suddenly feel very unwell. 

Unlike the common cold, flu causes people to suddenly feel very unwell.

A cold usually progresses harmlessly. The ill effects often fade away within a week, whether or not they have been treated.

In contrast, with the flu it takes a while before the person is fully recovered. Sometimes it is also a good idea to consult a doctor.

Nevertheless, what the common cold and the flu have in common is that treatment is aimed primarily at alleviating the symptoms. As yet, even against flu viruses, the only medications available can, at best, slightly shorten the duration of the illness.

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The video below explains the differences between a cold and a flu: the different triggers, symptoms, treatment options, and possibilities of a more severe course.

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What are the symptoms of the flu?

Genuine flu is also known as influenza. Many of its symptoms resemble those of the common cold or COVID-19: fever, achy head and limbs, and a blocked or runny nose may occur.

However, the flu affects the entire body, not just the airways. Flu viruses strike quickly and fiercely. Most really nasty ill effects usually fade away a lot within a week. But fatigue and coughing often last longer.

Typical flu symptoms include:

  • temperature between 38°C and 40°C or higher
  • muscle and joint pain all over the body
  • headaches
  • sore throat
  • chills
  • extreme fatigue and a very ill feeling
  • dry coughing without phlegm
  • a blocked or runny nose
  • loss of appetite
  • extreme tiredness
Typical symptoms of influenza include high temperature (from 38°C to 40°C or higher), headache, muscle pain, joint pain, severe fatigue and lassitude, dry cough, rhinitis (sneezing, itchiness and a blocked or runny nose), loss of appetite.

What causes flu?

Flu is caused by viruses. Viruses are tiny, microscopic germs even smaller than bacteria. Once they get into the body, viruses multiply quickly. To combat a viral infection, the human body’s defense system forms antibodies – but it needs time to do so.

There are hundreds of flu viruses that are collated into groups. Virus groups Influenza A and Influenza B are the most dangerous.
Someone who has had the flu develops an immunity to the specific flu virus that caused their illness. However, nobody is permanently protected after suffering from flu: the viruses are constantly changing, so completely new types of virus can emerge from year to year.

How does flu develop?

The flu is very often followed by an inflammation of the sinuses (sinusitis). When sinusitis occurs, the cavities around the nose are filled with an infectious fluid. Frequent complaints include headaches and a blocked nose. 

In babies and infants, infections of the air ways often lead to an inflammation of the middle ear.

Flu rarely develops into a severe infection. Complications such as pneumonia are not common. This is primarily a risk for people with a weakened immune system. In most cases, these are infants and young children, people with lung or immune diseases, and people over the age of 60. If the flu becomes very serious, it may be life-threatening.

How can flu be prevented?

Cold and flu viruses are spread by droplet (airborne) infection. A sufferer scatters droplets containing the virus when coughing and sneezing. And when cleaning one's nose, viruses can get from the handkerchief to the hands, and from there reach other people or objects.

For example, many people touch the doorknobs and handles on public transport, so the viruses can easily be transmitted from person to person. Direct contact by shaking hands or hugging can also spread cold and flu viruses.

To protect oneself and others from the illness, the most effective course of action is to prevent spreading these viruses. For example, it is important to wash your hands thoroughly, to cough into your elbow rather than into your hand, to ventilate rooms regularly and to dispose of used paper tissues immediately.

Even when flu sufferers are on the mend, they remain infectious for up to one more week. So during this time it is advisable to avoid social contact if possible and, for example, to work from home.

A flu vaccine can also provide protection. However, because flu viruses are constantly changing (mutating), an annual booster is required to ensure proper immunization protection.

Following vaccination, it takes the body around 14 days to build up sufficient antibodies. To ensure protection over the entire flu season, it is essential to receive a vaccination before the first cases of flu occur – in Europe, the best time for vaccination is autumn. However, as flu outbreaks can occur in January, February or even later, late vaccination can still be effective.

For more information about how vaccination offers protection against flu and the groups for whom vaccination is recommended, see gesundheitsinformation.de.

How is flu treated?

With flu, the first step is to rest until the symptoms have passed. Many people opt for homespun remedies such as chicken broth and herbal teas to alleviate the effects of flu. It is also felt that one should drink plenty. However, it is not scientifically proven that these measures help fight flu. So there is no need to use these homespun remedies or to drink much more than one wants to.

There are many commercially available products, such as vitamin supplements and inhalation devices, to combat colds, coughs and flu. There is no convincing evidence that these speed up recovery, either.

Painkillers like paracetamol, acetylsalicylic acids (ASA) and ibuprofen can alleviate pain and reduce fever.

Important: The active ingredient acetylsalicylic acid (ASA) is not suitable for children and adolescents. It can cause a rare but dangerous side-effect: Reye syndrome – a disease that particularly affects the brain and liver and which is life-threatening.

As well as the over-the-counter medicines mentioned, there are specific flu drugs. Oseltamivir, in particular, is used in Germany. Oseltamivir is only available on prescription and must be taken within 2 days from the start of the illness. If the symptoms have been there for longer, the drug can no longer affect the progress of the flu. There is evidence that oseltamivir could shorten the duration by just under one day. However, it often causes nausea and vomiting.

Antibiotics cannot help with flu, as antibiotics only act against bacteria and not against viruses.

In cooperation with the Institute for Quality and Efficiency in Health Care (Institut für Qualität und Wirtschaftlichkeit im Gesundheitswesen) (IQWiG).

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