How Contagious is the Flu? Find Out the Facts Here

The flu is highly contagious, spreading easily from person to person. Learn how contagious it is and how to protect yourself from this common virus.

The flu is a serious illness caused by influenza viruses. It’s known for spreading quickly.1 Symptoms can start suddenly and affect your whole body.

Common signs are fever, cough, and feeling tired.1 When someone with the flu coughs or sneezes, they spread tiny droplets. These droplets can enter the air and then go into people’s mouths or noses. This is how the flu viruses move from person to person.1 Flu can also spread by touching something with the virus and then touching your face.

Anyone can get the flu. But, it’s most dangerous for young kids, the elderly, and those with weak immune systems. It can even be deadly for them.1 To protect yourself, getting a flu shot each year is your best bet against the flu.

Key Takeaways

  • The flu is a highly contagious respiratory illness caused by influenza viruses.
  • Flu viruses spread primarily through respiratory droplets from coughing, sneezing, or talking.
  • The flu can also spread through contact with contaminated surfaces or objects.
  • Annual flu vaccination is the best way to prevent the flu and reduce the risk of serious complications.
  • The flu can be a serious illness, especially for young children, older adults, and those with weakened immune systems.

Understanding the Influenza Virus

Influenza, or the flu, is a very contagious illness. It’s caused by the influenza virus. This virus affects the nose, throat, and sometimes the lungs. It causes a variety of symptoms of different severity levels.2

What is Influenza (Flu)?

The flu attacks the respiratory system. It mainly hits the nose, throat, and lungs. Its symptoms show up fast. You might get a fever, cough, or have a sore throat. You can also feel tired, have body aches, or a headache.3 Not everyone gets a fever with the flu. But it can still make you quite sick. Sometimes, it can even lead to death.2

Flu Symptoms

Common flu signs are fever, headache, and sore throat. You might feel very tired and achy, or have a cough. Other symptoms include sneezing, a runny nose, and upset stomach.3 The flu can range from mild to severe. It might lead to serious problems like pneumonia. It can also cause ear infections or dehydration.2

Learning about the flu virus and its symptoms is key. This helps us know and act when we or our loved ones get sick. We can take steps to keep safe from the flu’s bad effects.

How the Flu Spreads

The flu virus is mainly spread through the air by people who are already infected. When these people cough, sneeze, or talk, tiny droplets can fly into the air.4 If you’re close enough, these droplets might land in your mouth or nose. This could make you sick.4

Person to Person Transmission

Being near someone who has the flu is the most common way to catch it. This happens when an infected person’s droplets touch your face.4 You can also get the flu by touching something with the virus on it. Then, if you touch your face, the virus might enter your body.4

Airborne and Surface Spread

The flu can also spread another way. It goes through tiny particles in the air.4 These particles can stay in the air or on surfaces for a while. If someone breathes them in, they could get sick too.4 Staying away from sick people and keeping your hands off of things many people use can protect you. This helps avoid both airborne and surface spread.4

how flu spreads

When Are People with Flu Contagious?

The flu virus can be detected in most infected individuals starting one day before symptoms develop and up to five to seven days after becoming sickis flu contagious>.3 People with the flu are most contagious during the first 3 days of being ill.3 Certain groups, like young children and those with weak immune systems, might spread the flu for longer.3

The flu contagious periodcontagious period> usually starts about a day before symptoms show. It can last up to a week or more after getting sickis flu contagious>.3 In this period, the virus can easily spread to others through coughing, sneezing, or close contact.4

Knowing the flu infectious periodinfectious period> is key to stop the flu from spreading.3 Good hygiene, staying away from sick people, and getting medical help with flu symptoms are all important.4

How Contagious is the Flu?

Seasonal Incidence Estimates

About 8 percent of the U.S. gets flu every season. The number can vary, hitting between 3 percent and 11 percent. This depends on how bad the season is.4 To find this, we divide the number of flu cases by the total population.4

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Age and Susceptibility Factors

Kids from 0 to 17 years old usually show a flu rate of 9.3%. Adults 18 to 64 come in just a bit lower, at 8.8%. But, those 65 and older have the lowest rate, only 3.9%.4 The number of people getting sick changes with the flu season. It can range from 3 percent in mild seasons to 11 percent in tougher ones.4

Flu Severity and Contagiousness

The number of people catching the flu changes with how bad the flu season is. In 2011-2012, when the flu season was mild, about 3% of Americans got sick.4 But in the more serious seasons like 2012-2013 and 2014-2015, up to 11% got infected.4 When the flu is worse, it spreads more easily.

Mild vs. Severe Flu Seasons

How many people get the flu can change a lot. For example, in 2011-2012, only 3% of people got sick. This was seen as low severity. But in tougher times like 2012-2013 and 2014-2015, about 11% got the flu. These moments were considered moderate to high severity.4 The flu’s impact changes with how bad the season is.

Impact on Transmission Rates

When the flu season is bad, it can spread more easily. Each year, around 8% of Americans catch the flu. This number can go as low as 3% in milder seasons, or as high as 11% in severe cases.4 Kids up to 17 mostly get affected, with 9.3% getting sick. For adults, the numbers are a bit lower. Those 18-64 have an 8.8% chance of getting the flu. The 65 and older group has the lowest risk at 3.9%.4

High-Risk Groups for Flu Infection

Young kids, the elderly, and those with weak immune systems face serious risks from the flu. It’s important to know this to keep them safe. We need to plan out ways to help them fight off the flu.

Young Children

Kids under 18 are at a bigger risk of catching the flu than adults over 65. Research shows they have a 9.3% chance of getting the flu. This is much higher than the 3.9% chance seen in the elderly.4

Older Adults

Adults 65 and older, as well as those with weak immune systems, face serious complications from the flu. The CDC says most flu deaths and many hospital stays happen in this group.5

Individuals with Weakened Immunity

If you have asthma, diabetes, or heart disease, the flu can hit you hard. It can make your health problems worse and cause serious illnesses like pneumonia.5

It’s vital to know who is at high risk and protect them. This means making sure they get their flu shots and medicines. By doing so, we can lower the flu’s impact and keep our communities healthier.

Flu Complications and Risks

Flu can lead to serious problems, especially for those at higher risk.6 Common issues include pneumonia, ear infections, and dehydration.


Pneumonia is a dangerous comp- lication of the flu.6 It can come from the flu virus directly or by making the body weaker to bacteria. For those with health issues, the risk is higher.

Ear Infections

Flu can also cause ear infections, mainly in kids.6 This happens when the flu virus causes the ears to fill with fluid. It leads to pain, fever, and can harm the ears if not treated.


Dehydration often follows the flu from high fever and not drinking enough.6 It’s especially risky for the very young and the elderly. Severe cases might need hospital care.

Hospitalization and Mortality

Severe flu can mean a hospital visit or even death.6 This risk is highest for young kids, the elderly, and those with health problems. Timely medical attention is critical.

Knowing the dangers of the flu is essential, particularly for vulnerable groups.6 Vaccination and quick treatment can reduce the chance of severe complications and lower flu risks.

Preventing Flu Transmission

The best way to stop the flu is by getting the flu shot each year.4 It’s advised for everyone aged 6 months and up.3 You can also stop the flu by cleaning your hands often and not getting too close to sick people.7 Doing these things keeps you and others safe from this respiratory sickness.

Importance of Annual Flu Vaccination

Kids over six months should get the flu shot, especially if they’re at high risk.3 About 2 to 3 percent of American kids are allergic to eggs, which affects flu shot safety.3 But, most of these kids can still get vaccinated safely with some care, and severe cases should see a pediatric allergist.3

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Good Hygiene Practices

The flu spreads fast, often before symptoms show.7 After someone gets sick, they can still spread the flu for about a week. This makes the risk of spreading it high.7 Coughing and sneezing can send the virus up to six feet away, so it’s important to take steps to prevent it.7 One crucial step is washing your hands a lot, especially after being around someone ill.7 Using hot water to wash things like towels and clothes can kill the flu virus, which is key during its peak time.7

Flu Treatment Options

If you catch the flu early, antiviral drugs can make a big difference.8 They reduce how bad the flu gets and shorten how long you’re sick.8 It’s also okay to use over-the-counter drugs like acetaminophen or ibuprofen for comfort.8 But, with any treatment, the flu requires rest and lots of fluids to fully recover.

Antiviral Medications

Flu antiviral drugs are most effective when started within two days of feeling sick.8 They lessen the illness’s impact and make you sick for a shorter time.8 Early use might even prevent serious complications like pneumonia.8 These drugs are especially crucial for those that are at high risk.8 However, healthy people often don’t need these antiviral medications.8

Over-the-Counter Symptom Relief

Over-the-counter meds such as acetaminophen or ibuprofen can make flu symptoms more bearable.8 Remember, antibiotics don’t fight the flu and can have negative side effects.8 Masks on sick people can reduce the flu’s spread, and clean hands are key in stopping it.8 It’s wise to stay home until you’re better to avoid getting others sick.8 Also, fresh air and clean indoor air are helpful in lowering virus risks.8

Flu and Travel Considerations

Flu can happen any time, with the most cases seen depending on the time of year in each part of the world.9 In the North, the flu is common from October to May.9 The South sees it more from April to September.9 If you’re traveling, especially with lots of different people, you might face a higher chance of catching the flu.2

Seasonal Patterns Worldwide

The flu hits hard in the North from October to April or May, and in the South from April to September.9 In tropical areas, the flu is around all year.9 Knowing when flu is more likely can help travelers be ready for outbreaks at their destination.

Heightened Risks for Travelers

Traveling, especially with many people or on ships, can mean more chances to get or spread flu.2 It’s key to be current on your flu shot,9 making sure to get it at least two weeks before leaving home so it has time to work.9 Plus, keeping your hands clean, obeying local health advice, and watching for signs of flu for a week after you get back can lower the risk of spreading flu.9

Flu SeasonNorthern HemisphereSouthern HemisphereTropical Regions
Peak SeasonOctober – MayApril – SeptemberYear-round
Vaccination TimingFall (ideally 2 weeks before travel)Fall (ideally 2 weeks before travel)Year-round (ideally 2 weeks before travel)
Increased Exposure RiskTravel with international groups, cruise shipsTravel with international groups, cruise shipsTravel with international groups, cruise ships

Tracking Flu Outbreaks and Trends

The CDC and state health departments watch the flu closely. They check where it’s spreading and how bad it is. Then, they tell us about any big flu problems happening near us or all over the country.10

Local and National Surveillance

About 100 public health labs and 300 clinical labs all over the U.S. help watch out for the flu.10 They collect info to see how much flu is out there, what kind of flu it is, and how it’s affecting people.10 Symptoms of the flu can happen to anyone, so they look at samples from different age groups.10 They also send certain samples for further tests, especially of different kinds of flu viruses.10 This helps them keep an eye on how the flu is changing and if our vaccines still work.10 They also test the flu viruses to see if they can resist certain medicines.10 And they’re always on the lookout for new types of flu that might start spreading among people.10

Online Resources and Updates

Looking at websites like and health department pages can tell us a lot about the flu. We can find the newest info on how much flu is around, the types of flu, and how to not get sick.11 Since October 1, 2023, the CDC has checked over 4,600 flu viruses to see what they are and how they might affect us.11 They give tips on how to stop the flu from spreading more and what to do if a new dangerous flu pops up.11

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Watching flu outbreaks and reading up on flu surveillance can prepare us. We can know what’s going on with the flu and what steps to take to protect ourselves. Staying informed is key to preventing big flu problems.


The flu is an illness that spreads quickly because it is easy to pass from one person to another. It mostly spreads through the air when someone sick coughs or sneezes.12 You can spread the flu even before you feel sick, and for a few days after. The worst time for spreading it is in the first three days of feeling sick.12 Younger people are more likely to get sick than older adults are.12 It’s good to get the flu shot every year and wash your hands often to help stop the flu from spreading. The flu affects a lot of Americans every year, ranging from 5 to 20 percent.13

In the past, there were big flu outbreaks known as pandemics.13 Examples include the “Spanish” flu (1918-1919), “Asian” flu (1957-1958), and “Hong Kong” flu (1968-1969). These happen when a new type of flu affects people who have little or no immunity to it.13 These outbreaks can cause a lot of sickness and death. The Spanish flu, for instance, killed over 500,000 people in the U.S. and around 50 million worldwide. A big part of those who died were young and otherwise healthy.13

Knowing how easily the flu can spread and what makes it spread more, we can do things to protect ourselves and others.1213 It’s important to do what we can to keep the flu from spreading. Each of us can make a difference in staying healthy and keeping our communities safe from this serious illness.1213


What is the flu and what are its symptoms?

The flu is a very contagious sickness caused by influenza viruses. Its symptoms come on fast. They include fever, cough, sore throat, and more.

How do flu viruses spread?

Flu viruses mainly spread through droplets when infected people cough, sneeze, or talk. These droplets can land in others’ mouths. Flu can also spread by touching surfaces with the virus on them.

When are people with the flu most contagious?

People are most contagious with the flu in the first 3 days of being sick. Some, like young children and those with weak immune systems, might spread it for longer.

How contagious is the flu compared to other seasons?

Each season, about 8% of the U.S. gets the flu. How severe the season is changes this number. Worse years mean more people get the flu.

Who is most at risk for severe flu illness?

Young kids, older adults, and those with weak immune systems face the most risk. They might need hospital care. For them, the flu is more likely to lead to serious problems or even death.

What are some common flu complications?

Complications from the flu can be serious, like pneumonia or dehydration. They might need hospital treatment. Some at-risk groups, like the very young or old, have a higher chance of severe complications.

How can the flu be prevented?

To stop the flu, get a flu shot every year. Also, practice good hygiene. Cover your mouth when you cough, wash your hands often, and avoid sick people.

How is the flu treated?

To treat the flu, start with antiviral medications early. You can also take over-the-counter drugs for symptom relief. Rest and drink plenty of fluids are crucial for getting better.

How does travel impact flu risk?

Traveling, especially in big groups, can up your flu risk. Be cautious of flu seasons where you’re going. Make sure you’re vaccinated before heading out.

Where can I find the latest information on flu activity?

The CDC and state health groups watch flu activity closely. Check their websites for the newest updates on flu, including tips to stay healthy.

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