Influenza (also known as the flu) is a contagious respiratory illness caused by flu viruses. It can cause mild to severe illness, and at times can lead to death. The flu is different from a cold. The flu usually comes on suddenly. People who have the flu often feel some or all of these symptoms:

• Fever* or feeling feverish/chills
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle or body aches
• Headaches
• Fatigue (tiredness)
• Some people may have vomiting and diarrhea, though this is more common in children than adults.

* It's important to note that not everyone with flu will have a fever

Everyone who is at least 6 months of age should get a flu vaccine this season. It’s especially important for some people to get vaccinated. Those people include the following:

• People who are at high risk of developing serious complications like pneumonia if they get sick with the flu
• This includes
• People who have certain medical conditions including asthma, diabetes, and chronic lung disease.
• Pregnant women.
• People 65 years and older.
• People who live with or care for others who are at high risk of developing serious complications
• This includes household contacts and caregivers of people with certain medical conditions including asthma, diabetes, and chronic lung disease.

CDC recommends that people get vaccinated against influenza as soon as the flu season vaccine becomes available in their community. Influenza seasons are unpredictable and can begin as early as October.

It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against the flu.

Flu vaccine is produced by private manufacturers, so availability depends on when production is completed. If everything goes as indicated by manufacturers, shipments are likely to begin in August and continue throughout September and October until all vaccine is distributed.

Doctors and nurses are encouraged to begin vaccinating their patients as soon as flu vaccine is available in their areas, even as early as August.

Flu vaccines are offered in many locations, including doctor’s offices, clinics, health departments, pharmacies and college health centers, as well as by many employers, and even in some schools.

Even if you don’t have a regular doctor or nurse, you can get a flu vaccine somewhere else, like a health department, pharmacy, urgent care clinic, and often your school, college health center, or work.

A flu vaccine is needed every year because flu viruses are constantly changing. It’s not unusual for new flu viruses to appear each year. The flu vaccine is formulated each year to keep up with the flu viruses as they change.

Also, multiple studies conducted over different seasons and across vaccine types and influenza virus subtypes have shown that the body’s immunity to influenza viruses (acquired either through natural infection or vaccination) declines over time.

Getting vaccinated each year provides the best protection against influenza throughout the flu season.

Yes. If you get sick, there are drugs that can treat flu illness. They are called antiviral drugs and they can make your illness milder and help you feel better faster. They also can prevent serious flu-related complications, like pneumonia. For more information about antiviral drugs.

Flu seasons are unpredictable in a number of ways. Although epidemics of flu happen every year, the timing, severity, and length of the epidemic depends on many factors.  These factors include what influenza viruses are spreading, whether they match the viruses in the vaccine, and how many people get the vaccine.

The timing of flu is very unpredictable and can vary from season to season. Flu activity most commonly peaks in the United States between December and February.  However, seasonal flu activity can begin as early as October and continue to occur as late as May.  It is not possible to predict how mild or severe a flu season will be.

Flu viruses are constantly changing so it's not unusual for new flu viruses to appear each year. For more information about how flu viruses change, click on the link: Key Facts About Seasonal Flu Vaccine and the 'Flu Season' tab. 

A number of different manufacturers produce both trivalent (three component) and quadrivalent (four component) influenza vaccines for the U.S. market.  These vaccines can be delivered in multiple ways, including intramuscular (IM), intradermal, and nasal spray. See Key Facts About Seasonal Flu Vaccine for more information about the different types of vaccines available in the United States. 

Manufacturers have projected that they will produce between 171 million and 179 million doses of flu vaccine for the U.S. market.  

The influenza vaccine for the United States is produced by a number of different vaccine manufacturers who are licensed by the Food and Drug Administration. The CDC does not produce flu vaccine.

Flu vaccines are designed to protect against the main flu viruses that research suggests will be the most common during the upcoming season. Three kinds of flu viruses commonly circulate among people today: influenza A (H1N1) viruses, influenza A (H3N2) viruses, and influenza B viruses.

All of the 2015-2016 influenza vaccine is made to protect against the following three viruses:

• an A/California/7/2009 (H1N1)pdm09-like virus
• an A/Switzerland/9715293/2013 (H3N2)-like virus
• a B/Phuket/3073/2013-like virus. (This is a B/Yamagata lineage virus)  

Some of the 2015-2016 flu vaccine is a quadrivalent vaccine and also protects against an additional B virus (B/Brisbane/60/2008-like virus). This is a B/Victoria lineage virus.  Vaccines that give protection against three viruses are called trivalent vaccines. Vaccines that give protection against four viruses are called quadrivalent vaccines.  More information about influenza vaccines is available at Preventing Seasonal Flu With Vaccination.

Flu is a serious contagious disease that can lead to hospitalization and even death.

CDC urges you to take the following actions to protect yourself and others from influenza (the flu):  

• While there are many different flu viruses, the flu vaccine protects against the three viruses that research suggests will be most common.  
• The 2015-2016 vaccine will protect against an influenza A H3N2 virus, an influenza B virus and the H1N1 virus that emerged in 2009 to cause a pandemic.
• Everyone 6 months of age and older should get a flu vaccine as soon as the 2015-2016 vaccines are available.
• Vaccination of high risk persons is especially important to decrease their risk of severe flu illness.
• People at high risk of serious flu complications include young children, pregnant women, people with chronic health conditions like asthma, diabetes or heart and lung disease and people 65 years and older.
• Vaccination also is important for health care workers, and other people who live with or care for high risk people to keep from spreading flu to high risk people.
• Children younger than 6 months are at high risk of serious flu illness but are too young to be vaccinated. People who care for them should be vaccinated instead.

Take everyday preventive actions to stop the spread of germs.

• Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it.
• Wash your hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub.  
• Avoid touching your eyes, nose and mouth. Germs spread this way.  
• Try to avoid close contact with sick people.  
• If you are sick with flu–like illness, CDC recommends that you stay home for at least 24 hours after your fever is gone except to get medical care or for other necessities. (Your fever should be gone without the use of a fever-reducing medicine.)  
• While sick, limit contact with others as much as possible to keep from infecting them. 

Take flu antiviral drugs if your doctor prescribes them. 

• If you get the flu, antiviral drugs can treat your illness.  
• Antiviral drugs are different from antibiotics. They are prescription medicines (pills, liquid or an inhaled powder) and are not available over-the-counter.  
• Antiviral drugs can make illness milder and shorten the time you are sick. They may also prevent serious flu complications.  
• It’s very important that antiviral drugs be used early (within the first 2 days of symptoms) to treat people who are very sick (such as those who are hospitalized) or people who are sick with flu symptoms and who are at increased risk of severe flu illness, such as pregnant women, young children, people 65 and older and people with certain chronic health conditions.  
• Flu-like symptoms include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills and fatigue. Some people also may have vomiting and diarrhea. People may be infected with the flu, and have respiratory symptoms without a fever. 

Visit CDC’s website to find out what to do if you get sick with the flu and how to care for someone at home who is sick with the flu.