Influenza (the flu) is a contagious respiratory illness caused by influenza viruses. There are two main types or strains of influenza virus; types A and B. Influenza A and B viruses are responsible for seasonal flu epidemics each year.
Seasonal influenza refers to the flu viruses that circulate during the winter months each year and for which vaccines are created to protect people each season.
Every year in the United States, 5-20% of the population gets the flu, more than 300,000 people are hospitalized from flu complications, and an average of 30,000 die from flu-related causes. Some people, including those over 65 or under five years of age, and people with certain conditions, such as pregnancy, asthma, arthritis, lupus, diabetes, cancer, HIV/AIDS, heart or kidney disease, or morbid obesity, are at high risk for serious flu complications.
The main way that influenza viruses are spread is person to person by "droplet spread." This happens when droplets from a cough or sneeze of an infected person are propelled through the air and deposited on the mouth, nose, or eyes of people nearby. Influenza viruses may also be spread when a person touches respiratory droplets on an object and then touches their mouth, nose, or eyes before washing their hands.
The flu usually comes on suddenly and may include these symptoms:
Influenza causes mild to severe illness and can be fatal.
It can take one to four days (average two days) from when a person is exposed to flu virus for symptoms to develop.
Most healthy adults may be able to infect others beginning one day before symptoms develop and up to five days after becoming sick. Children and immune-compromised people may pass the virus for longer than ten days. That means that a person may be able to pass on the flu to someone else before they feel ill, as well as during their illness. Some people can be infected with flu virus but have no symptoms. During this time, they can still spread influenza to others when they sneeze or cough.
Generally, a person infected with a certain strain of influenza virus will have some immunity to closely related viruses – this immunity may persist for one or more years. The degree of protection depends on the health of the person. Young and healthy people with strong immune systems will likely have good immunity against the same or closely related viruses from one year to the next. However, people with weakened immune systems are less likely to have immunity that carries over to other years. It's important to remember that influenza viruses are constantly changing, so, over time, immunity against one strain is less effective against strains.
Complications of flu can include bacterial pneumonia, ear infections, sinus infections, dehydration, and worsening of chronic medical conditions, such as congestive heart failure, asthma, and diabetes.
Yes. The single best way to prevent the flu is to get a flu vaccine each year. Within two weeks of vaccination, antibodies develop that protect against influenza virus infection. There are several flu vaccine options for the 2020-2021 flu season.
Trivalent flu vaccines protect against two strains of influenza A and one strain of influenza B. Quadrivalent vaccines protect against an additional strain of influenza B. The nasal spray flu vaccine (live attenuated influenza vaccine or LAIV) is also available for use for the 2019-2020 flu season.
Trivalent flu vaccine available this season include:
Quadrivalent flu vaccines available this season include:
For detailed information regarding this season's flu vaccines, click here.
Persons with a history of egg allergy who have experienced only hives after exposure to egg can receive any licensed flu vaccine that is otherwise appropriate for the recipient’s age and health status. Persons who report having had reactions to egg involving symptoms other than hives, such as angioedema, respiratory distress, light headedness, or recurrent vomiting, may similarly receive any licensed flu vaccine that is otherwise appropriate for the recipient’s age and health status. Studies indicate severe allergic reactions in people with egg allergies are unlikely. People who have severe egg allergies should be vaccinated in a medical setting and be supervised by a health care provider who is able to recognize and manage severe allergic conditions.
It is recommended that all people six months of age or older get a flu vaccine. Everyone, every year!
Because they are at high risk of serious flu-related complications or because they live with or care for high risk persons, it is especially important for the following people to get an annual flu vaccine:
Cover your mouth and nose with a tissue when coughing or sneezing.
Wash your hands after disposing of used tissues. If you don’t have a tissue, sneeze or cough into your sleeve, not your hands
Clean your hands.
Washing your hands often will help protect you from germs. When soap and water are not available, alcohol-based disposable hand wipes/sanitizers may be used.
Avoid touching your eyes, nose or mouth.
Germs are frequently spread when a person touches something that is contaminated with germs and then touches his or her eyes, nose, or mouth.
Practice other good health habits
Get enough sleep, be physically active, manage your stress, drink plenty of fluids, and eat nutritious food.
Use antiviral drugs as prescribed by your healthcare provider to treat and prevent the flu.