What does the flu virus consist of?


The flu, a viral disease which attacks the respiratory system, is caused by the influenza virus.


Flu affects the nose, throat and lungs.


Unlike bacterial infections, which can be treated with antibiotics, viral infections can only be prevented with vaccines since antibiotics are ineffective against viruses.

The following are a few differences between viruses and bacteria:


Viruses are groups of tiny genes, such as the flu virus.

  • They invade and destroy cells
  • They depend on the host to reproduce
  • Only vaccines prevent infection


Bacteria are microscopic organisms.

  • They can be beneficial, neutral or harmful
  • They can reproduce by themselves
  • They can be combatted with antibiotics

Types of flu viruses

The influenza virus is divided into 3 types: A, B and C. Because each type of flu strain circulates simultaneously every year, the yearly vaccines include up to 4 sub-types (usually 2 from type A and 2 from type B, which are the main causes of seasonal flu).


Influenza A

Infects birds, human beings and other mammals

Causes pandemics

Mutates very quickly


Influenza B

Infects human beings (especially children)

Causes epidemics

Mutates quickly


Influenza C

Infects human beings and swine (pigs and piglets)


Mutates slowly

Swine flu and bird flu

Unlike the subtypes we have just seen, which primarily affect human beings, there are also other subtypes of viruses that are less frequent yet no less virulent. Some of these subtypes, as you can read further down, have actually caused some of the largest pandemics in the past century.

H1N1 (swine flu)

  • Subtype of influenza A
  • Infects swine
  • Can affect humans (rarely)
  • Symptoms similar to seasonal flu
  • Caused the 2009 pandemic

H5N1 (bird flu)

  • Subtype of influenza A
  • Infects water birds and fowl
  • Can affect humans
  • Fatal symptoms (high mortality rate)
  • Alarm in 2003 for fear of a pandemic

What is the difference between a cold and the flu?

The first symptoms appear: sore throat, cough, fever… Is it a cold or the first symptoms of a flu? To help you distinguish them more easily, we’ve developed this comparative table which will help you to better identify the problem so you know how to act in order to treat your symptoms correctly.




Slight fever (or no fever)
How quickly it appears
Level of fatigue
Muscle pain
Sore throat
No pain

Common or seasonal flu

If the majority of the symptoms you are suffering from are similar to the flu, it’s pretty likely that you’ve got what is called the common or seasonal flu. In any event, we recommend that you always check with your family doctor, who can help you more easily distinguish the symptoms and monitor them properly.

Even though the flu virus is around throughout the year, many more people become infected with it in the winter months. The reasons are that the virus lives better in the cool, dry winter air, and that in the winter we spend more time inside enclosed places because of the cold.

How do you catch it?



The flu virus can spread to other human beings starting the day before you even notice any symptoms, and this lasts 5 to 7 more days, so it can even be spread before you know you’re ill.


Entry into the body

In order to infect others, the virus only needs to penetrate the organism through the mucous membranes of the respiratory tract, mouth or eyes.



Once the virus has entered the body, all it has to do is reach the lung cells and start replicating.

Basically, we can say that there are three ways in which the virus can be transmitted:


Through direct contact with someone who has the flu


Through small particles released when coughing or sneezing


Through the air (the least common way)

Therefore, its capacity for transmission is high.

Especially in schools and workplaces, a person infected with the flu virus can actually infect their colleagues in just 2 or 3 weeks.


The symptoms often come within the first 2 or 3 days after entering into contact with the virus. Its symptoms are quite characteristic and follow a common pattern, as shown below:


Low fever

Fully-body ache


Flushed face



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Dry cough

Slight difficulty breathing

Nasal drip


Sore throat


The majority of symptoms disappear, but the cough, the fatigue and even the fever may last a few more days.

You may not fully recover your appetite for another few days.

How to avoid and prevent the flu

As we mentioned above, the flu virus has to enter your body and replicate after having entered your lung cells. To prevent this from occurring and to avoid infection, a few simple preventative steps are recommended:

To avoid it

Wash your hands frequently with soap and water

Avoid touching your face (especially the mucus membranes in your mouth, nose and eyes)

Keep away from people who are coughing or sneezing

To prevent it

Build your defenses all year round with a healthy diet

Eat vitamin C-rich food every day, especially as the winter begins

Get a flu vaccine (remember that it changes every year)

What does the flu vaccine consist of?

The way the flu vaccine works is very simple. Just like all other vaccinations, it consists of exposure to the dead or highly weakened virus so that your body can generate antibodies, protecting you against future infection.

Nonetheless, it is between 70% and 90% effective, since it is impossible to predict which strains will spread the most throughout the winter season. Therefore, even if you have been vaccinated against 4 different strains, this does not mean that you cannot be infected by another of the 2 or 3 strains that might become predominant during the year.

Should I get the flu shot?

Even though the vaccine does not always prevent the flu, it can reduce the symptoms in people who need it the most. It is particularly recommended for the highest risk groups:

People over the age of 65

People with chronic cardiovascular or lung diseases (including people with asthma)

Workers at healthcare centers

Pregnant women

How to treat the flu

If you have followed our recommendations and taken precautions but have still caught the flu, we can still offer you a bit of help. Even though having the flu is neither easy nor pleasant, with these tips you can lower your infection time and alleviate your symptoms as much as possible.


Drink plenty of liquids to replace the fluids you lose from sweating and fever


Rest and sleep more than 8 hours a day


Avoid doing any kind of activity


Take medication that improves your symptoms (such as those that lower fever)

Worldwide flu outbreaks

You have probably heard about the great pandemics, cases when the flu has spread all over the world. Even though they are rare, isolated cases, there have been 4 major global outbreaks in the past 100 years. Do you know about all of them?

  • During the last year of World War I, the virus spread from the city of San Sebastián to the rest of Europe, particularly affecting soldiers on the battlefield.
  • After eliminating the epidemic, the virus came back months later much more virulent, killing more people more quickly.
  • The pandemic spread across America, Asia and India, killing 500 million people.
  • This virus originated in Asia (Beijing), and was responsible for killing 5 million people worldwide.
  • A mutation of the H2N2 virus leapt from swine to infect human beings.
  • It spread so quickly because of the increased speed of transportation and international flights.
  • Originating in birds, this virus caused the death of almost 2 million people.
  • It originated in Hong Kong and spread around Europe via the British who travelled to this Southeast Asian enclave.
  • The last outbreak was unleashed in Russia in 1997 after the bird flu, which also originated in Hong Kong.
  • In this case, the virus, a strain of H1N1 which was nicknamed the swine flu, consisted of a genetic mix of a human virus, two swine viruses and a bird virus.
  • It originated in Mexico and spread from there to the rest of the world. Even though there were fears that it would propagate quickly and become deadly, the strain ended up not being overly lethal and harmful.


Health Minister – Health also travels: http://www.msssi.gob.es/profesionales/saludPublica/sanidadExterior/salud/home.htm
Bellvitge Travel (OMS authorized centre): http://www.bellvitgetravel.com/
Barnaclínic International Traveller Centre: http://www.barnaclinic.com/savi/index.html?servei
WHO, international trips and health: http://www.who.int/ith/es/
Travel requirements for yellow fever: http://www.who.int/ith/ITH_Annex_I.pdf?ua=1
Vaccines: http://www.who.int/ith/ITH_chapter_6.pdf?ua=1
Malaria: http://www.who.int/topics/malaria/es/