People are usually most infectious when they have a fever. Most adults shed the influenza virus within the first week of illness, but it persists longer in children. (Photo: Shutterstock)

Influenza myth busters

Here is everything you need to know about the flu.

Influenza season is upon us, and Susanne Gjeruldsen Dudman, a senior medical officer for vaccine preventable diseases at the Norwegian Institute of Public Health, has offered to address the most common questions and fallacies about the flu.

Why does the influenza virus most commonly strike in the winter?

It may be that the virus survives longer when it is colder, and that it is more effective in infecting people when the air is cold and dry.

We’re also more likely to be indoors, and thus in closer contact with people, which increases the likelihood of infection. Schools and kindergartens are open, and children are very effective in spreading illnesses.

Less sunshine in winter can also result in lower levels of vitamin D. This reduces the body’s resilience and may increase a person’s risk of infection.

Fever isn’t just bad. It can actually help inhibit a viral infection. (Illustrative photo: Colourbox)

The peak of the flu season either comes around Christmas or a little later, but outbreaks typically last from October to mid-May the following year.

The exception is, of course, if there is an influenza pandemic with a new virus that no one is immune to. These come on very suddenly.  In 2009, the H1N1 virus, which was new, started in late summer and peaked in November.

Is it important to avoid getting cold to avoid getting the flu? If so, what part of the body needs the most protection? Your feet? Your lungs?

You should avoid freezing all parts of your body.

Should I be vaccinated even though I have had the flu in the last six months?

The recommendation is that people be vaccinated for the flu before the beginning of each flu season.

What part of the body does the influenza virus attack first? Is it your lungs, your throat or your head?

Influenza viruses primarily attack the respiratory tract. They access the body via the upper part of the respiratory tract, but the virus can also spread from the throat down to the lungs.

Why does my entire body ache?

The muscle pain is probably due to high levels of interferon, which is part of the body’s immune response. Viruses have been found in muscle tissue as well.

Does fever play a roll in limiting the illness, or can you take a fever-reducing pill and recover as quickly?

High fever may affect the virus.

This is what an influenza virus looks like in an electron microscope. The image is artificially colored. (Picture: Cybercobra at English Wikipedia, CC-BY-SA 3.0)

Why do some people get sick and others do not, even if both people have been infected and are equally healthy?

They may have different immune responses from previous illnesses or vaccines. People may have also been exposed to different amounts of virus when they were infected. There are also many other unknown factors that cause the illness to affect people differently.

How long am I contagious after I start feeling bad?

People are usually most infectious when they have a fever. Most adults have shed the influenza virus within the first week of illness, but it persists longer in children.

Some vaccines contain live viruses. What is the difference between the live and inactivated vaccine?

A live vaccine provokes an immune response that is more similar the protection you get from a natural infection. It can often completely prevent infection initially, while an inactivated vaccine inhibits the spread of the virus. The effect of a live vaccine also lasts longer than from an inactivated vaccine.

Do you have to be in good health to get a live vaccine?

People who have impaired immune systems from disease or who are pregnant may be best off avoiding live vaccines. Although the (live) virus is weakened in this type of vaccine, it can nevertheless cause the flu in these groups.

What ends a flu epidemic? Is it because of vaccines, or because enough people have been infected and become immune and create herd immunity?

Both vaccines and infections in the population increase the proportion of the population that is immune. That limits the epidemic.

How long are you immune to influenza after you have had the flu?

You are only immune to the kind of flu you were infected with. A part of the immune system response to a particular virus type disappears after a few months, while other parts last for several years and can prevent serious infection with the same type of virus.

How many times can you get the flu during your lifetime?

Actually, there is no upper limit.

Want to know more? Check out the Norwegian Institute for Public Health’s English-language webpages on influenza.


Read the Norwegian version of this article at

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