How can I avoid getting the flu?

Seasonal influenza (or “flu”) is most often caused by type A or B influenza viruses. Symptoms include sudden onset of fever, cough (usually dry), headache, muscle and joint pain, sore throat and a runny nose. The cough can be severe and can last two or more weeks. Most people recover from fever and other symptoms within a week without requiring medical attention. However, influenza can cause severe illness or death in high-risk groups (see ‘Who is most at risk?’ below).

Seasonal epidemics occur mainly during winter, from October to March in the northern temperate regions and April to September in the southern temperate regions. In the tropics, influenza circulates year-round with one or more periods of increased circulation.

The best way to reduce your risk of getting sick and prevent severe illness is to get the seasonal flu vaccine. Influenza viruses evolve continuously, and WHO makes global recommendations to update the vaccine composition twice a year.

WHO recommends annual vaccination for high-risk groups including health care workers, pregnant women, older adults, and people with chronic medical conditions. People should get vaccinated just before the start of the influenza season for the most effective protection, although getting vaccinated at any time during the influenza season can still help prevent flu infections. It can take up to two weeks after vaccination for the body to develop protection (antibodies) against the influenza virus.

Measures like opening windows and avoiding crowded, closed spaces can also reduce the risk. See ‘How do you stop it from spreading?’ below.

Flu spreads through tiny particles released into the air when a person with the virus coughs, sneezes, talks, or breathes. A person can catch the influenza virus by being close to someone who is sick or by sharing the same closed space. It can also be spread by hands contaminated by the virus.

People who feel sick should stay home, as far as possible. If they are in crowded spaces, they should wear a mask.

Measures to limit the spread of flu include:

• increasing ventilation, such as by opening windows, to improve indoor air quality and flow;
• avoiding crowded, closed spaces;
• covering the nose and mouth with a tissue when coughing or sneezing, and throwing out the tissue after use;
• cleaning hands regularly; and
• cleaning high-touch surfaces regularly.

People most at risk for severe seasonal influenza are:

• pregnant women at any stage of pregnancy;
• children younger than 5 years;
• people older than 65 years;
• people with chronic medical conditions such as asthma, heart and lung diseases and diabetes;
• people with suppressed immune systems, due to chemotherapy or conditions such as HIV; and
• people with increased risk of exposure to influenza, which includes health-care workers.

People with the flu should drink plenty of water and rest. Most people begin to feel better within a week. WHO suggests that people who are at higher risk of severe illness are given antiviral medicines, as these medicines help reduce complications and the risk of dying. They work best when taken early, ideally within 48 hours after symptoms begin. Antibiotics are not effective against viruses, including influenza.

Seasonal flu outbreaks are caused by small changes in the viruses that are already circulating, and to which many people have some immunity.

Flu pandemics are caused by new influenza viruses that most people don't have immunity to. If such viruses acquire the ability to spread easily between people, they can easily infect many more people, leading to a pandemic.

Seasonal influenza viruses may contribute to the emergence of a pandemic virus (for example if a seasonal influenza virus mixes with an influenza virus currently circulating in animals). Once a pandemic virus has circulated and stabilized over a period of time in a population, as with the pandemic A(H1N1) in 2009, it can become a seasonal virus.