How Does Influenza Spread?
Influenza spreads from person to person, mainly via droplets generated when people with the flu sneeze, cough, or talk. These droplets can infect others up to about 6 feet away if they enter their mouths or noses. Though less common, the flu can also be transmitted by touching an object or surface that has the flu virus on it and then touching the mouth, nose, or eyes.8 People who carry the flu virus are most highly contagious within the first three to four days after they get sick. Still, most healthy adults can infect others a day before symptoms develop and up to seven days after they become ill. People with weakened immune systems and children may be contagious for even longer. Most often, symptoms begin around two days after the virus finds its way into the body.8
How To Prevent the Flu
According to the Centers for Disease Control and Prevention (CDC), the best way to prevent seasonal influenza is to get the annual flu vaccine. Robust evidence suggests that the flu vaccine prevents many people from getting sick. If people do get sick after getting vaccinated, their illness is less severe. Vaccination also reduces the risk of flu-associated hospitalization, can be lifesaving for children, and can protect people with chronic health problems from developing serious symptoms of the flu.9
Because the influenza virus is constantly evolving, the World Health Organization convenes twice a year to identify viruses for inclusion in seasonal influenza vaccines.10
The CDC recommends an annual influenza vaccine for everyone aged 6 months or older. CDC guidelines state that pregnant people and people with certain chronic conditions can get the flu shot but should avoid certain types of vaccines and some defined groups should not get the vaccine:11
- People with severe, life-threatening allergies to ingredients in the flu vaccine
- People who have had a severe allergic reaction to a dose of influenza vaccine before
The CDC states that influenza vaccines help the body develop antibodies within about two weeks and are available in both shot and nasal spray form.12 The nasal spray vaccine is made from a live but weakened virus and is designed to protect against four flu viruses: two strains of influenza A and two strains of influenza B. The CDC only recommends the spray for healthy people between the ages of 2 and 49 who are not pregnant, and it warns that people with certain medical conditions should not use the nasal spray vaccine.13
Prevention Beyond Vaccines
Generally, good health habits are also helpful precautions against influenza. These include:14
- Washing your hands often with warm water for 30 seconds (the time it takes to sing “Happy Birthday” two times)
- Using hand sanitizer
- Keeping distance from those who are sick
- Staying home from work, school, and other public places when sick
- Covering your mouth and nose with a tissue or elbow—not your hands—when sneezing or coughing.
Who Is at Risk From the Flu?
Some people are at higher risk of developing serious complications from the flu. They include:15
- Adults 65 and older
- Pregnant people
- People with asthma, cancer, or HIV/AIDS
- People with certain disabilities
- People with heart disease, diabetes, or chronic kidney disease
- People who have had a stroke
Some racial and ethnic groups experience higher rates of severe influenza. This includes people who are non-Hispanic Black, American Indian or Alaska Native, Hispanic, or of Latin descent.16