Key Facts About Seasonal Influenza (Flu)

What is Influenza (Also Called Flu)?

The flu is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness, and at times can lead to death. The best way to prevent the flu is by getting a flu vaccination each year.

Every year in the United States, on average:

• 5% to 20% of the population gets the flu;
• more than 200,000 people are hospitalized from flu complications; and
• about 36,000 people die from flu.

Some people, such as older people, young children, and people with certain health conditions (such as asthma, diabetes, or heart disease), are at high risk for serious flu complications.

Symptoms of Flu

Symptoms of flu include:

• fever (usually high)
• headache
• extreme tiredness
• dry cough
• sore throat
• runny or stuffy nose
• muscle aches
• Stomach symptoms, such as nausea, vomiting, and diarrhea, also can occur but are more common in children than adults

Complications of Flu

Complications of flu can include bacterial pneumonia, ear infections, sinus infections, dehydration, and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes.

How Flu Spreads

Flu viruses spread mainly from person to person through coughing or sneezing of people with influenza. Sometimes people may become infected by touching something with flu viruses on it and then touching their mouth or nose. Most healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5 days after becoming sick. That means that you may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick.

Preventing Seasonal Flu: Get Vaccinated

The single best way to prevent the flu is to get a flu vaccination each year. There are two types of vaccines:

• The "flu shot" – an inactivated vaccine (containing killed virus) that is given with a needle. The flu shot is approved for use in people 6 months of age and older, including healthy people and people with chronic medical conditions.
• The nasal-spray flu vaccine – a vaccine made with live, weakened flu viruses that do not cause the flu (sometimes called LAIV for “Live Attenuated Influenza Vaccine”). LAIV is approved for use in healthy* people 2-49 years of age who are not pregnant.

About two weeks after vaccination, antibodies develop that protect against influenza virus infection. Flu vaccines will not protect against flu-like illnesses caused by non-influenza viruses.

When to Get Vaccinated

Yearly flu vaccination should begin in September or as soon as vaccine is available and continue throughout the influenza season, into December, January, and beyond. This is because the timing and duration of influenza seasons vary. While influenza outbreaks can happen as early as October, most of the time influenza activity peaks in January or later.  

Who Should Get Vaccinated?

In general, anyone who wants to reduce their chances of getting the flu can get vaccinated. However, certain people should get vaccinated each year either because they are at high risk of having serious flu-related complications or because they live with or care for high risk persons. During flu seasons when vaccine supplies are limited or delayed, the Advisory Committee on Immunization Practices (ACIP) makes recommendations regarding priority groups for vaccination.

People who should get vaccinated each year are:

1. Children aged 6 months up to their 19th birthday
2. Pregnant women
3. People 50 years of age and older
4. People of any age with certain chronic medical conditions
5. People who live in nursing homes and other long-term care facilities
6. People who live with or care for those at high risk for complications from flu, including:
   a.   Health care workers
   b.   Household contacts of persons at high risk for complications from the flu
   c.   Household contacts and out of home caregivers of children less than 6 months of age (these children are too young to be vaccinated)
   

Use of the Nasal Spray Flu Vaccine

Vaccination with the nasal-spray flu vaccine is an option for healthy* people 2-49 years of age who are not pregnant, even healthy persons who live with or care for those in a high risk group. The one exception is healthy persons who care for persons with severely weakened immune systems who require a protected environment; these healthy persons should get the inactivated vaccine.

Who Should Not Be Vaccinated

Some people should not be vaccinated without first consulting a physician. They include:

• People who have a severe allergy to chicken eggs.
• People who have had a severe reaction to an influenza vaccination in the past.
• People who developed Guillain-Barré syndrome (GBS) within 6 weeks of getting an influenza vaccine previously.
• Children less than 6 months of age (influenza vaccine is not approved for use in this age group).
• People who have a moderate or severe illness with a fever should wait to get vaccinated until their symptoms lessen.

If you have questions about whether you should get a flu vaccine, consult your health-care provider.

* "Healthy" indicates persons who do not have an underlying medical condition that predisposes them to influenza complications.