An infectious disease MD explains for how long you're likely to transmit the flu to others, with her best advice for preventing viral infection.
How Long Are You Contagious With the Flu? An Expert Doctor Reveals
Published on Feb. 05, 2025
About the expert
Linda Yancey, MD, is a board-certified physician in infectious disease and internal medicine with over two decades of experience practicing in Texas. She completed her residency at Mayo Clinic in Scottsdale, Arizona, and pursued a fellowship at Baylor College of Medicine in Houston. Currently, Dr. Yancey serves as an infectious disease specialist at Memorial Hermann Hospital in Houston.
Highlights
- People with the flu can be contagious before they show any symptoms.
- The best protection against the flu is vaccination.
- Antiviral medications work best within 48 hours of symptom onset.
- Staying home when you’re sick helps stop the spread to others.
Each year, millions of people come down with the flu (influenza), leading to missed workdays, school absences, and plenty of time spent under the covers with tissues and a cup of warm tea. According to the Centers for Disease Control and Prevention (CDC), influenza has caused anywhere from 9.3 million to 41 million illnesses annually between 2010 and 2024. In recent years, respiratory viruses seem to be hitting harder and spreading faster, making it more important than ever to have clarity on how long you’re contagious with the flu.
If you or someone in your household has been struck by classic flu symptoms like fever, chills, and body aches, you understand how vital it is to protect yourself and those around you. This is especially true for those most at risk, including newborns, pregnant women, older adults, and individuals with weakened immune systems.
Ahead, Linda Yancey, MD, a board-certified infectious disease specialist at Memorial Hermann Hospital in Houston, explains how long the flu remains contagious and shares her expert doctor guidelines for preventing its spread.
How long is someone who has the flu contagious?
Dr. Yancey says, “People are contagious with the flu starting the day before symptoms appear and lasting about a week.” However, young children, older adults, and those with weakened immune systems may continue to spread the virus for a longer period, sometimes up to two weeks. “People are most contagious in the first few days of illness, which is why it’s important to stay home when you’re sick or wear a mask if you need to go out,” she adds.
Ideally, individuals should remain at home until they fully recover. When that’s not an option, wearing a mask in public, washing your hands with soap and warm water frequently, and following other good hygiene rules can help reduce the risk of spreading the virus to others.
What to do if you were exposed to the flu
“The most effective way to lower the risk of getting the flu is to get the flu shot,” Dr. Yancey advises. The vaccine not only helps prevent some cases entirely but also makes infections that do occur much less severe. In addition to vaccination, wearing a mask in crowded indoor spaces or places you’re most likely to catch the flu offers another layer of protection. “Both in combination is even safer,” she says.
If you’ve been exposed to the flu, pay close attention to any early symptoms—fever, chills, fatigue, or body aches—since the flu can develop within a few days of exposure. Washing your hands frequently, avoiding touching your face, and maintaining good hygiene can reduce the likelihood of infection. Supporting your immune system is also key. Staying hydrated, eating nutrient-rich foods, and getting plenty of sleep can help your body fight off illness.
In some cases, antiviral medications like oseltamivir (Tamiflu) or baloxavir (Xofluza) may be an option, especially for those at higher risk of severe illness. These medications work best when taken within 48 hours of symptom onset, so if you’re concerned, reach out to a healthcare provider as soon as possible.
How to prevent the spread of the flu
No one likes being sidelined by the flu, but even worse is unknowingly spreading it to those most vulnerable—like newborns, older adults, people living in communal settings, and individuals with weakened immune systems. Fortunately, taking a few precautions can help keep people safe.
Dr. Yancey advises: “People can protect their at-risk friends and family by getting the flu shot, masking when they’re sick, and staying home to recover from respiratory illnesses.”
In addition to those important steps, here are some other ways to stop the flu in its tracks:
- Wash your hands frequently: Scrub with soap and water for at least 20 seconds, especially after coughing, sneezing, or touching shared surfaces.
- Cover your coughs and sneezes: Use a tissue or your elbow to prevent airborne germs from spreading.
- Clean high-touch surfaces: Wipe down surfaces like doorknobs, light switches, and cell phones regularly to kill lingering viruses.
- Avoid touching your face: The flu virus can enter through your eyes, nose, or mouth, so keep your hands away when possible.
- Maintain good airflow: Open windows when possible or use air purifiers to help reduce the concentration of airborne germs indoors.
- Stay hydrated and rest up: A strong immune system starts with good hydration, a balanced diet, and plenty of sleep.
How long does the flu last?
“People will have the worst symptoms for three to five days, but it can take up to two weeks to fully recover from an average case of the flu,” Dr. Yancey says.
While the most intense phase of fever, chills, and body aches typically subsides within a few days, lingering fatigue and a persistent cough can stretch recovery time.
When to see a doctor
Most cases of the flu can be treated at home with rest and fluids, but certain signs require urgent medical attention. These include, but are not limited to:
- Difficulty breathing or shortness of breath
- Persistent chest pain or pressure
- A high fever that won’t break
- Severe dehydration (signs include dizziness, dry mouth, or little to no urination)
- Flu symptoms that improve but then return with a worse fever and cough—this could indicate a secondary infection
- Confusion or sudden disorientation, especially in children or older adults
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