What is the flu?
Influenza is an infectious disease, caused by the Influenza A and B viruses, which mainly affects the respiratory tract and usually occurs in winter.
Generally, it is a short-lived illness with moderate symptoms. Patients over the age of 65 or immunocompromised may have milder signs and symptoms, but recovery may be slower and the risk of problems and complications is higher.
The flu vaccine has been important in reducing the risk of transmitting the virus and developing severe illness and complications in case of infection.
Learn more at Flu and COVID-19 vaccination.
How is the flu virus transmitted?
The influenza virus is transmitted by the respiratory route, directly person-to-person, by close contact (about 2m). Viruses contained in an infected person's respiratory secretions, which are expelled through coughing, sneezing or talking, can infect another person.
Transmission can also occur through direct contact with parts of the body, for example through the hands, with surfaces contaminated with the virus, and then by touching the eyes, nose or mouth.
What is the incubation period of the virus?
The incubation period, i.e. the period between the time the person is infected and the appearance of the first symptoms, is usually 2 days, but can vary between 1 and 4 days.
What is the period in which an infected person can infect others?
Generally, the contagion period starts 0-24 hours before the onset of symptoms, peaks at 24-48 hours, and then declines rapidly with almost no virus detected after 5-10 days.
In children, patients over 65 years of age, chronic disease, obese and immunocompromised, this period may be longer.
What are the signs and symptoms of the flu?
In adults, the symptoms are:
- malaise and tiredness
- high fever
- muscle and joint pain
- headaches
- sore throat
- cough
- nasal congestion
In young children, the symptoms are similar to those in adults. In younger children, flu symptoms may include:
- high fever
- cough
- rhinitis
- headache and muscle aches
- red throat and eyes
- nausea and vomiting
- diarrhea
- difficulty breathing
How is the flu diagnosed?
Diagnosis is essentially clinical, through the identification of symptoms and signs.
What is the difference between the flu and cold?
Although both are viral infections, the flu and cold are not caused by the same viruses and have some different symptoms.
The symptoms of a cold appear milder than those of the flu. They are often limited to the nose area and are not as associated with serious complications.
The symptoms of the flu tend to be more intense than those of a cold, and muscle aches, tiredness and a higher fever are more common. In addition, there is an increased risk of developing complications or worsening pre-existing conditions.
Is it possible to prevent the flu?
Yes. We can try to avoid contagion by adopting some preventive measures, namely through annual vaccination, according to the indications of the Directorate-General for Health or the attending doctor.
Sick people should not:
- Share the same room
- Kiss or hug
Sick people should:
- Keeping your distance from others
- Wear a mask
- Ventilate interior spaces
- Disinfect common areas
- Wash your hands frequently
- Maintain respiratory etiquette:
- cover your mouth/nose with a handkerchief or arm when sneezing or coughing
- Do not sneeze/cough into your hands
- washing hands after coughing/sneezing
Learn more at Prevent respiratory infections.
Can the flu develop into more serious complications?
Influenza is usually a short-lived illness (2 to 4 days), with symptoms of moderate intensity and benign evolution, and complete recovery takes about 1 to 2 weeks.
In risk groups – people with chronic diseases and the elderly – recovery may be longer and the risk of complications is higher, namely, pneumonia or decompensation of the underlying disease (asthma, diabetes, heart disease, lung disease, cancer).
What should I do if I have the flu?
In case of flu:
- Stay at home on bed rest (usually up to 24 hours after you stop having a fever)
- Avoid contact with others while you are sick
- Keep the air clean (open a window to air out)
- Measure temperature throughout the day
- If you have a fever you can take paracetamol (even for children)
- Use saline to relieve nasal congestion
- If you live alone, especially if you have mobility limitations or are ill, you should ask someone to call you regularly to find out how you are doing
It is very important to note that:
- If you are pregnant or breastfeeding, do not take medication without talking to your doctor
- Do not take antibiotics without a doctor's recommendation, as they do not act on viral infections, improve symptoms or speed up healing Drink plenty of fluids (water and fruit juices)
What time of year is it most common?
The flu usually occurs in the winter months. In Portugal, in recent years, it has been found that the greatest flu activity occurs in the autumn and winter months (between October and April), with the peak recorded between November and February.
Is there a flu vaccine?
Yes. Flu viruses are constantly changing, and vaccine immunity is not long-lasting. For this reason, people should be vaccinated every year.
Learn more at Flu and COVID-19 vaccination.