The First Symptoms of the Flu

The flu is a viral infection that is transmitted from person to person and is very common in cold weather. If you want to recognize the first symptoms of the flu, in this article we'll tell you about them.
The First Symptoms of the Flu

Last update: 16 December, 2022

When cold weather arrives, many people will catch the flu, but what exactly is it? Well, it’s an infection caused by a virus. Throughout this article we’ll explain more details, focusing especially on the symptoms of the flu that help us to recognize it.

What is the flu?

The flu is an acute viral infection that usually affects the upper respiratory tract. The causative microorganism is the Influenza virus , of the Orthomyxoviridae family.

Although there are different types, the most common and relevant for people is the type A influenza virus. Within this type, we find different subtypes, based on two proteins that viruses have on their surface: hemagglutinin (HA) and neuraminidase (NA). These proteins undergo changes and mutations:

  • If the variations are small, they give rise to seasonal flu, which is usually easily transmitted in cold weather.
  • On the other hand, if these mutations are more extensive, they give rise to different subtypes of influenza viruses. These produce greater resistance, are the cause of pandemics, and are the ones that raise the number of affected people.

Flu symptoms and incubation period

Flu symptoms can vary, depending on whether it’s a mild, moderate, or severe infection. Still, the onset of flu symptoms is usually sudden, usually including:

  • Fever: This can range from mild to moderate or high. Normally, it’s reduced with the use of antipyretics and usually lasts between 1 and 7 days, the most frequent being 3 days.
  • Headaches: Normally, it’s a generalized pain and it isn’t throbbing.
  • Muscle pain, especially in the back of the body, in the thighs, and in the lower back.
  • Chills and a feeling of cold, even when very clothed.
  • General weakness and tiredness or fatigue, which can even cause dizziness or vertigo when standing up.
  • Sore throats, which usually makes swallowing difficult.
  • A dry cough that normally doesn’t lead to mucus or expectoration.
  • Red or watery eyes: the so-called “glassy eyes”, characteristic of the flu.
  • Nasal congestion
  • Nausea, vomiting, and diarrhea: These are more frequent symptoms in children, while they aren’t so in adults.
Throat pain.

You may be interested in: Vertigo: Symptoms, Causes and Treatment

The incubation period for influenza is usually a maximum of two days, and, as we have mentioned, it has a sudden onset, between 3 and 6 hours. The first symptoms are usually fever, a feeling of general malaise, and pain in different parts of the body.

In general, the symptoms are similar year after year, although they may have small variations, some of them being more characteristic in each season.

Who is affected the most by the flu?

The manifestations of the influenza virus infection depend, among other factors, on the person’s age and basic health.

In terms of age, children are more susceptible to more pronounced flu symptoms, in part because their immune systems are still immature.

Influenza virus infection is clearly marked by the coldest seasons of the year. Transmission of the virus occurs from person to person, being easier in crowded places. An infected person can transmit the virus from the day before the onset of the first flu symptoms, up to approximately seven days later.

Prevention of the flu and its symptoms

To prevent the flu, or at least its most severe symptoms, vaccination of the so-called risk groups is recommended, made up of the people most susceptible to virus infection and its complications. These risk groups include:

A pregnant woman.
  • Being pregnant
  • Boys and girls between 6 and 23 months of age.
  • People over 65 years of age.
  • Poultry and pig farm workers.
  • People between 2 and 64 years of age who suffer from other diseases or pathologies, such as diabetes, heart disease, morbid obesity, kidney or liver failure, autoimmune diseases, cancer, HIV or congenital immunodeficiencies.

In addition to vaccination, other measures to reduce the probability of infection are:

  • Washing your hands frequently
  • Using a tissue when coughing or sneezing
  • Following a correct diet
  • Avoiding sudden changes in temperature
  • Avoiding getting cold
  • Maintaining proper ventilation of homes.
It might interest you...
The 5 Differences Between Colds and the Flu
Muy Salud
Read it in Muy Salud
The 5 Differences Between Colds and the Flu

Do you understand the differences between colds and the flu? Read on and discover 5 ways you can distinguish them.




Los contenidos de esta publicación se redactan solo con fines informativos. En ningún momento pueden servir para facilitar o sustituir diagnósticos, tratamientos o recomentaciones provenientes de un profesional. Consulta con tu especialista de confianza ante cualquier duda y busca su aprobación antes de iniciar o someterse a cualquier procedimiento.