Influenza, or the flu, is a common and highly contagious respiratory illness. A person develops this illness as a result of contracting an influenza virus.

It is likely that most people will experience the flu at least once during their lifetime. Some people may experience only mild symptoms. However, those with a weakened immune system may experience severe and even life threatening complications.

People at higher risk can take certain steps to protect themselves from the viruses that cause the flu.

In this article, we discuss what the flu is, how long it lasts, and how to prevent it.

a woman with the flu on a subway train where she is showing no symptoms because she is in the incubation period for fluShare on Pinterest
After contracting the flu virus, a person may not experience symptoms for a number of days.

Influenza is a common and highly contagious illness that mainly affects the respiratory system. This system consists of the lungs, the airways, and the muscles necessary for breathing.

A person develops flu as a result of contracting an influenza virus.

Types of influenza virus

There are four main types of influenza virus: A, B, C, and D. According to the Centers for Disease Control and Prevention (CDC), the ones that routinely spread between people are influenza A and influenza B. Together, they are responsible for the seasonal flu epidemics that occur year after year.

Scientists further categorize influenza A viruses into subtypes, depending on the genes that make up the proteins on their surface. Influenza A includes up to 198 subtypes.

Many different possible combinations of influenza types and subtypes can occur each year. To develop effective flu vaccines, scientists must predict which combinations will be circulating during a given year.

For more information and resources to help keep you and your loved ones healthy this flu season, visit our dedicated hub.

The incubation period refers to the time between contracting an infection and experiencing symptoms. The World Health Organization (WHO) note that the typical incubation period for the flu is about 2 days but that it can range from 1 to 4 days.

The symptoms of flu typically last about 3 to 7 days in most cases. However, general feelings of fatigue can last for more than 2 weeks. Some people may experience complications that cause the symptoms to last longer.

The flu is most contagious during the first 3 to 4 days in which a person experiences symptoms. However, people who have the flu can pass the infection on a day before they develop any symptoms and up to 7 days after becoming ill.

People with a weakened immune system can remain contagious for longer. These people may include:

  • young children
  • older adults
  • pregnant women
  • people with underlying health conditions that affect the lungs or the immune system

Flu symptoms usually appear very quickly. They may include:

The flu also commonly causes fever, although not everyone will experience this symptom. Fever occurs as a consequence of the person’s immune system fighting off the infection.

A person who has the flu can spread the virus by coughing, sneezing, or talking. These activities cause tiny droplets or “aerosols” to enter the air.

The aerosols can carry the virus up to 6 feet away. Another person can contract the virus by inhaling the aerosols or by touching a surface where they have landed and then touching their mouth, nose, or eyes.

The flu is a common illness that most people will experience in their lifetime. Nonetheless, it is possible to reduce the risk of flu.

The most effective way of preventing the flu is to receive a yearly flu vaccine. There are also other measures that people can take to avoid contracting and passing on the flu.

Flu vaccines

Flu vaccines contain dead or inactive forms of the three or four flu viruses that scientists predict will be circulating in the upcoming flu season. The vaccine allows the immune system to identify the viruses and make antibodies that will be capable of fighting an active form of those viruses in the future.

Importantly, a flu vaccine will only be effective against the specific subtypes and combinations of viruses that it contains. As such, it is possible to undergo vaccination and still get an uncommon strain of influenza if that strain happens to be circulating.

Certain people are at increased risk of contracting the flu or developing complications. Due to this, the WHO recommend that the following people receive a yearly flu vaccination:

  • healthcare workers
  • children aged 6 months to 5 years
  • adults aged over 65 years
  • pregnant women
  • people with chronic health conditions

Other measures

Other measures that can help reduce the spread of the flu include:

  • washing the hands regularly
  • avoiding touching the mouth, nose, or eyes
  • avoiding close contact with people who have the flu
  • staying home while the flu is likely to be contagious
  • covering the nose and mouth when coughing or sneezing
  • keeping objects and surfaces clean at home
  • taking antiviral drugs if a doctor prescribes them

The flu is a common and highly contagious respiratory illness that occurs as a result of a group of viruses called influenza viruses. These viruses mostly spread through tiny droplets that people expel when coughing, sneezing, or talking.

The symptoms of flu typically develop quickly. A person can be contagious a day before showing symptoms and up to 7 days after becoming ill. A person who is ill should take steps to prevent spreading the virus to others.

Vaccines are the most effective way of preventing the flu. Experts recommend yearly flu vaccinations for healthcare workers, as well as people who are vulnerable to developing complications of flu. These individuals include young children, older adults, and people with underlying health conditions.