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Facts About Influenza for Adults

multi-ethnic group of adultsWhat is Influenza?

Influenza (flu) is a contagious viral infection primarily of the nose, throat, and lungs. Flu is caused only by the influenza virus, but many people confuse illnesses caused by other viruses or bacteria, including severe colds (rhinovirus) or “the stomach flu” (norovirus and other viruses and bacteria) with influenza.

Flu occurs mainly in the fall and winter months in the US and infects anywhere from 5-20 percent of the population each year. Flu seasons are unpredictable and can be severe. For example, between 1976 and 2006, estimates of flu-associated deaths in the US ranged from a low of about 3,000 to a high of about 49,000 people. Unfortunately, there is no way to know beforehand whether any one flu season will be mild or severe.

Flu Symptoms

Flu symptoms can include fever, aches, chills, tiredness, and sudden onset. Other symptoms may include cough, runny/stuffy nose, and /or sore throat. Unlike other common respiratory infections that are often called “the flu,” influenza can cause more severe illness that can result in complications leading to hospitalization and death. However, whether symptoms are mild or severe, people can still spread influenza virus to others. In fact, they can spread influenza even before the show any symptoms.

Flu Prevention

An annual flu vaccine is the best way to prevent influenza. The time to vaccinate is as soon as vaccine becomes available, which can even be by late summer, and any time throughout the influenza season. Vaccination is needed annually for the best protection, as the vaccine is usually updated from one season to the next to protect against the influenza viruses that are most likely to circulate and immunity to influenza declines over time.

Who Should Get Flu Vaccine? 

Annual influenza vaccination is recommended for everyone age 6 months and older. For adults, that means a vaccine each year. Pregnant women are specifically encouraged to get vaccinated and may receive the vaccine any time during their pregnancy. The vaccine is available in several forms:

  • The traditional injected vaccine includes inactivated (or killed) virus and is approved for everyone six months and older.
  • Nasal spray vaccine includes live, but weakened virus and is approved for healthy people age two through 49 years.
  • Intradermal vaccine that is injected into the skin rather than the muscle because it uses a smaller needle; includes inactivated (or killed) virus, and is approved for adults age 18 through 64 years, and may appeal to those who do not like needles.
  • High-dose vaccine containing four times the amount of antigen to induce a greater immune response in people 65 and older.

Vaccine Safety 

All types of influenza vaccines are safe and well tolerated. The injected vaccines may result in some mild soreness, redness, or swelling at the injection site lasting one to two days. Other possible mild side effects include a headache and low-grade fever for a day after vaccination. The nasal spray vaccine may result in a runny nose, headache, low-grade fever, sore throat, fatigue or cough after vaccination. The potential risks associated with influenza are much greater than the potential risks associated with vaccination.

Flu and Vaccine Facts

  • FACT: Influenza vaccines are safe and are the best way to help prevent influenza.
  • FACT: Every adult in the US should get the influenza vaccine every year.
  • FACT: Circulating influenza viruses change often, which affects how severe and how common the illness is from year to year.
  • FACT: Flu seasons are unpredictable and can be severe. Between 1976 and 2006, estimates of flu-associated deaths in the US ranged from a low of about 3,000 to a high of about 49,000 people.
  • FACT: In the US, more than 200,000 individuals are hospitalized by influenza every year, including 20,000 children.
  • FACT: Infants younger than six months cannot get influenza vaccine, but they are high risk of serious complications and hospitalization if they get the flu. The best way to protect them is by vaccinating everyone around them.
  • FACT: The flu is caused only by influenza virus. People often mistake other, less severe illnesses with influenza, like the common cold or the “stomach flu,” which is not influenza at all. Stomach illnesses are caused by other viruses, like norovirus, and many types of bacteria.
  • FACT: Total direct hospitalization costs of a severe influenza epidemic are estimated to be over $6 billion.
  • FACT: Influenza vaccine is needed every year because the immunity wears off over time and also because in most years the vaccine is updated to match circulating strains.
  • FACT: Influenza can make chronic conditions worse. It can be associated with heart attacks, make it harder for diabetics to control their sugar levels, make asthma worse, and lead to pneumonia.


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