Influenza (flu) is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness. Serious outcomes of flu infection can result in hospitalization or death. Some people, such as older people, young children, and people with certain health conditions, are at high risk of serious flu complications.
In the United States, flu season occurs in the fall and winter. While influenza viruses circulate year-round, most of the time flu activity peaks between December and February, but activity can last as late as May. The overall health impact (e.g., infections, hospitalizations, and deaths) of a flu season varies from season to season.
People with flu can spread it to others up to about 6 feet away. Most experts think that flu viruses spread mainly by droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Less often, a person might get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes.
People with flu are most contagious in the first three to four days after their illness begins. Most healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. Children and some people with weakened immune systems may pass the virus for longer than 7 days.
Symptoms can begin about 2 days (but can range from 1 to 4 days) after the virus enters the body. 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. Some people can be infected with the flu virus but have no symptoms. During this time, those people may still spread the virus to others.
Most people who get sick with flu will have mild illness, will not need medical care or antiviral drugs and will recover in less than two weeks. Some people, however, are more likely to get flu complications that can result in hospitalization and sometimes death. Pneumonia, bronchitis, sinus infections and ear infections are examples of flu-related complications. Flu also can make chronic health problems worse. For example, people with asthma may experience asthma attacks while they have flu and people with chronic congestive heart failure may experience a worsening of this condition triggered by flu. Below are the groups of people who are more likely to get serious flu-related complications if they get sick with flu.
If you’re pregnant, a flu shot:
Pregnant women also need a whooping cough (Tdap) shot. Talk to your doctor.
A yearly flu vaccine is the first and most important step in protecting against flu viruses. Everyone 6 months or older should get an annual flu vaccine by the end of October, if possible, or as soon as possible after October.
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.
Avoid close contact with sick people, avoid touching your eyes, nose, and mouth, cover your coughs and sneezes, wash your hands often (with soap and water), and clean and disinfect surfaces and objects that may be contaminated with flu viruses. If soap and water are not available, use an alcohol based hand sanitizer.
If you become sick, limit contact with others as much as possible. Remember to cover your nose and mouth with a tissue when you cough or sneeze, and throw tissues in the trash after you use them. 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 for 24 hours without the use of a fever-reducing medicine before resuming normal activities.)
If you get the flu, antiviral drugs can be used to treat flu illness. Antiviral drugs can make illness milder and shorten the time you are sick. They also can prevent serious flu complications, like pneumonia.
CDC recommends that antiviral drugs be used early to treat people who are very sick with the flu (for example, people who are in the hospital) and people who are sick with the flu and are at high risk of serious flu complications, either because of their age or because they have a high risk medical condition.