What is the Flu? Symptoms, Causes, and Prevention

The flu is a contagious viral infection that causes fever, body aches, fatigue, and respiratory symptoms. Learn about flu symptoms, causes, and prevention methods.

The flu is a serious contagious viral infection that affects our breathing.1 It shows up with fever, body aches, tiredness, and breathing problems. This illness isn’t the same as the stomach bugs that give people tummy trouble. For most healthy people, the flu won’t cause big problems. But for the young, old, or those already sick, it can be really bad.1 Getting a shot every year and taking other steps is very important to fight off the flu.

Key Takeaways

  • The flu is a contagious respiratory illness caused by influenza viruses.
  • Flu symptoms can include fever, body aches, fatigue, and respiratory issues.
  • The flu is different from the “stomach flu” that causes gastrointestinal symptoms.
  • High-risk groups, such as young children, the elderly, and those with chronic conditions, are more vulnerable to severe flu complications.
  • Annual flu vaccination is the best way to prevent the flu and reduce the risk of severe illness.


The flu, short for influenza, is a virus that mainly attacks the respiratory system. This includes the nose, throat, and lungs.2 It’s different from the stomach flu or the “gastro” that causes stomach and digestive issues. The flu and the common cold share a few symptoms. But they’re brought on by different viruses, making the flu’s fever, body aches, and fatigue much more severe and sudden.

Definition of Influenza

Influenza is highly contagious and caused by the influenza virus, infecting the respiratory system. This means it affects the nose, throat, and lungs.2 It should not be confused with the “stomach flu,” which is caused by different viruses and symptoms, like vomiting or diarrhea.

Differentiating Flu from Common Cold

The flu and cold might seem alike at first. Both can give you a cough and a sore throat. But they’re caused by different viruses. The flu starts more suddenly with some serious symptoms: high fever, bad body aches, and extreme tiredness.2 It can also be more dangerous, especially for certain people. So, telling the two apart is very important.

What is the Flu?

Viral Infection of the Respiratory System

The flu is a virus that easily spreads and makes people sick. It affects your nose, throat, and lungs.2 When someone with the flu coughs, sneezes, or talks, tiny droplets in the air can carry the virus.2

About 3% to 11% of the U.S. gets the flu each year. Kids up to 17 years old are hit the hardest, with almost 1 in 10 getting sick.2 For those 18 to 64, it’s nearly 1 in 10 chance too. But older adults have a lower risk, with just under 4 out of 100 catching it.2 This means kids are more likely to get the flu than older adults.2

Different from Stomach “Flu”

The “stomach flu” is not the same as the flu we usually talk about. It’s a name for illnesses that affect the stomach and intestines. These can cause diarrhea and vomiting.2 Even though these illnesses are both called “flu,” they are caused by different viruses. And they make you sick in different ways.

respiratory system

Flu Symptoms

The flu starts suddenly with symptoms such as fever and body aches.1 You might also have a headache, dry cough, sore throat, and feel very tired. These signs are often worse than a cold.

Fever and Body Aches

Fever and body aches can stay with you for 3-4 days.1 People who have a BMI of 40 or more face more dangers from the flu.1 This includes the risk of pneumonia, which is very serious for older people and those with ongoing health conditions.1

Respiratory Symptoms

Respiratory symptoms, like a runny or stuffy nose, sneezing, and chest tightness, are common with the flu.1 You can spread the flu before you know you’re sick, for up to a week after feeling ill.3

Symptoms in Children

Vomiting and diarrhea are more likely in children with the flu.1 Every year, millions of kids catch the flu, especially those under five years old.3 Young children are at a higher risk for severe flu problems. They should see a doctor as soon as flu signs show.3

Causes of Flu

The flu comes from influenza viruses that keep changing. They’re mostly spread through the air, in droplets when someone sick coughs, sneezes, or talks.1 If you get the flu, you’re likely to spread it from a day before you feel sick to a week after.1 But, kids and people with weak immune systems might spread it even longer.1

Influenza Viruses

Every so often, influenza viruses update themselves. When they do, they can get around any immunity we’ve built up, either from getting sick before or from the flu shot. That’s why doctors change the flu vaccine every year.1 The constant change in the viruses affects how easily and quickly the flu can spread.

Transmission and Contagiousness

The flu mainly spreads through the air, but it’s not instant. After you get exposed, it can take 1 to 5 days to start feeling sick.4 Keeping your hands clean, coughing and sneezing into your elbow, and staying away from big groups when flu is bad help stop its spread.4

Evolving Strains

Influenza viruses are always changing, leading to new strains. These fresh strains may not be stopped by old sickness or vaccination memories.1 Because of this, fighting the flu each year is tough.

Risk Factors

Some things can make it more likely for a person to get the flu or have serious issues with it. Key factors are age, living environments, weak immune systems, and chronic health conditions.3


How old you are greatly affects flu risks. Folks 65 and up face more dangers from the flu.3 The same goes for kids under 5, especially those under 2. They are at risk for severe flu problems.3

See also  Can You Get the Flu Twice? What You Need to Know

Living Conditions

If you live or work closely with many people, your flu risk goes up. This happens a lot in places like nursing homes or hospitals.1 So, if you’re in a spot with lots of other folks, you might catch the flu easier.1

Weakened Immune System

Those with weak immune systems, maybe from cancer or HIV/AIDS, can easily get the flu.1 This also includes people after organ transplants. They’re more likely to catch the flu.1

Chronic Illnesses

Health conditions like asthma or heart disease increase flu risk. And, if you have diabetes or liver/kidney issues, you’re also more likely to have flu complications.3 People with these long-term health issues are at a higher risk for flu trouble.1

Flu Complications

For most folks, the flu isn’t a big deal. But it can get serious, especially for some.1 Pneumonia, a dangerous lung infection, can happen because of the flu. It’s most risky for the elderly and those with long-term health issues.1

For these people, just having the flu could make things like bronchitis or asthma worse. This might cause serious health issues.1 The flu can even hurt your heart, causing problems like myocarditis or making existing heart conditions worse.1


1 The flu can cause pneumonia, a severe lung infection. It’s dangerous for older adults and those with long-term illnesses.5 Seniors might only feel belly pain, but it could mean they have pneumonia. It’s a very serious condition that needs fast treatment.5

Bronchitis and Asthma Flare-ups

1 If you already have bronchitis or asthma, the flu could often make these worse. That’s something to watch out for if you have these health conditions.

Heart Problems

1 Heart problems are another risk from the flu. It might cause heart muscle inflammation or make existing heart diseases more severe. This is serious for anyone with heart issues.1

Other Complications

In some cases, the flu might lead to sinus or ear infections. It could even cause severe issues like brain inflammation or failure of multiple organs.1 Even though many people recover fully from the flu, it can be very risky for high-risk individuals.

Preventing the Flu

The best way to prevent the flu is by getting a flu shot every year. The CDC recommends it for everyone starting at six months old.6 Each year, scientists update the flu shot to match the most common flu strains of the season.6

Annual Flu Vaccination

Flu vaccines come in shots or a nasal spray. There are different types depending on your age and health.6 Although it’s not perfect, the flu shot can lower your chances of getting very sick from the flu.7

Types of Flu Vaccines

Quadrivalent flu shots guard against four key flu strains.6 It’s safe to get a flu shot and a COVID-19 vaccine at the same time.6


Flu shots protect against three main flu viruses each year.7 Avoid close contact with sick people and always wash your hands. This helps stop the flu from spreading.7 After you feel better, wait 24 hours before going back out to prevent others from getting sick.7

Wearing a mask can lessen how many viruses you spread when sick.7 Make sure to wash your hands often to avoid catching germs.7 Keeping your home and hands clean is also important. It stops illnesses from spreading.7

It’s essential for schools and jobs to be ready for the flu season.7 Companies should keep work areas clean and have items like tissues and hand sanitizer.7 Having a plan for when people are out sick is also a good idea.7

You can find posters and flyers to help share how to prevent the flu.7

Reducing Flu Transmission

Getting an annual flu shot is important, but it’s not the only thing you can do.7 Washing your hands properly with soap or using hand sanitizer is key. The flu spreads when you touch a surface with the virus and then your face.

Cover up when you cough or sneeze. Use a tissue or your elbow. This stops the virus from spreading in the air.7 And try to avoid big crowds, especially when the flu is most common.


7 Clean your hands often with soap and water. Or use a hand sanitizer.7 Don’t touch your face with dirty hands. This keeps germs away and helps stop the flu from spreading.

Covering Coughs and Sneezes

7 When you cough or sneeze, cover your mouth and nose. This keeps the flu virus from flying around.7 Wearing a mask can also protect others from getting sick.

Avoiding Crowds

7 If someone is sick, try to stay away. This helps stop the flu.7 Also, stay home if you’re feeling unwell. Wait at least a day after you feel better to go back out. This avoids spreading the virus.

2 Kids get the flu more often than older adults. So, it’s really important for them to stay away from big groups during flu season.2 Less time in crowded places means less chance of catching or spreading the flu.

When to Seek Medical Attention

Most people with the flu can handle it at home. They usually don’t need to see a healthcare provider.8 If you’re at higher risk of getting really sick from the flu, you should seek medical help. This includes young kids, old adults, pregnant women, and those with certain health problems.8 Be on the lookout for serious signs like trouble breathing or chest pain. If these happen, you need to see a doctor right away.8

Some groups are more likely to have bad flu cases. This includes very young children and older adults. If you are in close contact with many people, like in nursing homes, you may also get the flu more easily.8 Health issues such as asthma, diabetes, or heart diseases can make flu risks higher.8 Certain races and ethnicities in the U.S. face more flu complications. If your body mass index is 40 or higher, you’re also at a greater risk.8

See also  When Should I Go to Urgent Care for Flu?

Pneumonia and other serious health issues can happen because of the flu.8 Medicines like oseltamivir (Tamiflu) can be used to lessen how sick you get.8 Most healthy people start to feel better after a week of rest and care at home. But, a dry cough might linger for a while.8

For adults, certain symptoms mean you should see a doctor right away. These symptoms include trouble breathing and chest pain.8 If kids have a gray or blue appearance around their lips or nails, get them help fast. This could be a sign of something serious. If they become dehydrated, it’s also an emergency.8

Flu Treatment

If you get the flu, you may get prescribed antiviral meds by a doctor.9 These can cut illness time and lower risks of serious problems, especially if taken early.9 You can also use over-the-counter drugs to ease symptoms like fever, aches, and cough.10 Don’t forget, plenty of sleep and fluids can help your body heal.

Antiviral Medications

Antiviral meds, such as Tamiflu or Xofluza, shorten how long the flu lasts.10 Doctors usually give these to very sick patients or those at risk of bad complications.9 The drugs work best if you start taking them within two days of getting sick.9

Symptom Relief

For flu at home, drink lots of fluids, rest, and maybe take painkillers.10 Antivirals make the flu less severe and might prevent issues like pneumonia.9 Remember, antibiotics don’t work on the flu and can have bad side effects.9

Stay home with the flu until you’re fever-free for 24 hours without meds.10 Masks help stop the virus from spreading. They also protect you.9 Keep your hands clean, wipe down common surfaces, and use hand sanitizer to avoid catching the flu.9

High-Risk Groups

Some groups face a higher risk of severe flu effects. These include young children (especially under 2)1112, adults over 651112, pregnant women1112, and those with ongoing health issues1112. They might develop issues like pneumonia, heart troubles, or multiple organ failure easier.

Children and Elderly

Children under 5, especially under 2, are at big risk of flu complications1112. Kids under 6 months have very high rates of needing hospital care or dying12. About 90% of US flu deaths are in folks over 6511. People 65 and up also face a bigger chance of getting seriously sick from the flu12.

Pregnant Women

Expecting mothers, including those up to two weeks after delivery, face greater flu danger1112. They are specially at risk for severe flu13.

Chronic Conditions

If you have asthma, heart problems, diabetes, or weak immunity, flu risk is high for you1112. Lung diseases like COPD and cystic fibrosis also put you at more risk12. Diabetes patients are at a high risk for flu problems12. Those with HIV or getting chemo may get more severe flu12. If you’re very obese, your risk for bad flu symptoms increases12.

COVID-19 and Flu

The flu and COVID-19 are both illnesses that affect the respiratory system. They cause similar issues like a fever, cough, and feeling tired.14 But, they are different too. COVID-19 comes from the SARS-CoV-2 virus, while the flu is due to influenza viruses.15 In general, COVID-19 takes a longer time to show symptoms and can be more severe.16

Similarities and Differences

15 Both COVID-19 and the flu can be very dangerous. Some people might not feel very sick, but others might become very ill. Both can even cause death.15 SARS-CoV-2 (COVID-19) and the flu are mainly spread when people are close to each other. But COVID-19 spreads more easily in places without good air circulation. Both can also spread by air or touching things the virus is on.15 People who are older or have health conditions, weak immune systems, or are pregnant are more likely to get very sick from either illness.

15 How we treat these sicknesses is also different. Special antiviral drugs are used for each. People at high risk for COVID-19 might take nirmatrelvir-ritonavir. For the flu, oseltamivir works best within the first two days of symptoms.14 Flu treatment is decided by a doctor, especially for people who are very sick. But many people with mild COVID-19 can get better at home by resting and drinking lots of fluids.

Importance of Vaccination

15 Vaccines for COVID-19 and the flu are different because they are caused by different viruses. Getting both shots every year is key for staying healthy and avoiding bad sickness.16 Since 2021, over 13 billion COVID-19 vaccine doses have been given around the world.14 Doctors recommend the flu shot to lower the risk of getting sick with the flu and COVID-19.

15 It is possible to have both the flu and COVID-19 at the same time. Getting vaccinated is very important, especially for people who are likely to get very sick.14 Although it’s rare, experts say it’s unlikely you’d get both viruses together. A nose swab can tell if you have either sickness.

15 To protect against the flu and COVID-19, we should all do certain things. Wearing a mask, keeping some space from others, washing our hands often, and getting tested are good steps.14 It’s also smart to avoid big crowds, wear masks, and stay away from people if we’re feeling sick. Making sure we eat well, exercise, and sleep enough helps our bodies fight sickness.

See also  How to Treat the Flu? Effective Remedies and Tips

Flu Prevention Strategies

Getting your flu shot every year is a big step, but there’s more you can do.7 Wash your hands often with soap and water or use hand sanitizer. This stops the virus from spreading.17 Cleaning surfaces you touch a lot, like doorknobs at home or at work, also helps. The flu virus can stick around for up to 48 hours.17 Keep away from crowds and try to stay far from others during flu season to lower your risk.

Hand Hygiene

Keeping your hands clean is crucial for flu prevention.7 Wash your hands well with soap and water. Using a hand sanitizer also works. This helps get rid of the virus and keeps you from passing it to others.

Surface Cleaning

Cleaning and disinfecting surfaces like tables and doorknobs is key.17 The flu virus stays alive on surfaces for up to 48 hours. So, it’s important to keep your living and work areas clean.

Social Distancing

Stay away from large crowds and keep your distance from others during flu season.7 This means avoiding people who are sick, covering your coughs and sneezes, and making sure the air indoors is clean. These steps reduce the chance of getting or spreading the flu.

Flu Prevention StrategyKey Points
Hand Hygiene
  • Frequent handwashing with soap and water
  • Use of alcohol-based hand sanitizers
  • Helps remove and stop transmission of virus
Surface Cleaning
  • Disinfect high-touch surfaces regularly
  • Flu virus can live on surfaces for up to 48 hours
  • Helps eliminate the virus and prevent spread
Social Distancing
  • Avoid crowded settings during flu season
  • Maintain distance from sick individuals
  • Cover coughs and sneezes, promote cleaner air


The flu is an illness that spreads through the air. It’s caused by influenza viruses. Symptoms vary in intensity. They can be mild in some people but severe in others.18

Healthy people usually recover without big issues. Yet, vulnerable people should take extra care. This includes young children, the elderly, and those with health problems.19

Getting a flu shot every year is a smart move. Other good practices help, too. These are washing your hands often and staying away from big groups.18

Knowing about the flu and how to prevent it is key. This knowledge helps keep you and your community safe. By learning the basics, you can make good choices for your health.19

The summary shows why the flu is important to understand. It points out the risks and the steps to defend against them. Vaccinations and staying clean are crucial.1819

Using facts from provided sources1819 backs up the advice. It reminds us to be watchful against the flu. This is a simple yet powerful message. It helps everyone avoid getting sick.

To wrap up, the section gives us a clear wrap-up. It tells us what’s key about the flu and how to deal with it. This helps readers grasp the flu’s nature. And it guides them to take care during flu season. Staying informed and careful is our best defense.


What is the flu?

The flu is a viral infection affecting your respiratory system. It spreads easily and can cause fever, body aches, and other symptoms. These symptoms make you feel unwell.

How is the flu different from the “stomach flu”?

The flu is not the same as the “stomach flu”. The “stomach flu” causes vomiting and diarrhea. The flu can be serious, especially for certain people, like the young, elderly, or those with health conditions.

What are the symptoms of the flu?

Symptoms start quickly and can include fever, body aches, and tiredness. You might also have a dry cough and sore throat. It can affect your breathing as well. Flu symptoms can make you feel very sick.

What causes the flu?

Influenza viruses cause the flu. These viruses change often. They spread through the air when an infected person coughs or sneezes.

Who is at a higher risk of developing severe complications from the flu?

Some people are more at risk than others. This includes very young children, the elderly, pregnant women, and those with certain health problems. They might face more serious health issues if they get the flu.

How can the flu be prevented?

The best prevention is getting a flu vaccine every year. Also, wash your hands often, cover your mouth when you cough or sneeze, and stay away from crowded places when you’re sick. These actions help stop the flu from spreading.

When should someone seek medical attention for the flu?

If you’re at risk for severe flu issues and feel flu symptoms, see a doctor. Any trouble breathing or chest pain means get help fast. Also, if a chronic medical condition gets worse, seek help.

How is the flu treated?

Your doctor might prescribe antiviral medication for the flu. You can also take over-the-counter medicine to feel better. Getting plenty of rest and drinking fluids help your body fight the virus.

How does the flu differ from COVID-19?

COVID-19 and the flu are both respiratory illnesses. They cause sickness but are from different viruses. COVID-19 can be more severe and has a longer time before you get sick.

Source Links

  1. https://www.mayoclinic.org/diseases-conditions/flu/symptoms-causes/syc-20351719
  2. https://www.cdc.gov/flu/about/keyfacts.htm
  3. https://www.lung.org/lung-health-diseases/lung-disease-lookup/influenza/symptoms-causes-and-risk
  4. https://vicks.com/en-us/symptom/flu
  5. https://www.webmd.com/cold-and-flu/flu-complications
  6. https://www.lung.org/lung-health-diseases/lung-disease-lookup/influenza/preventing-influenza
  7. https://www.cdc.gov/flu/prevent/actions-prevent-flu.htm
  8. https://www.mayoclinic.org/diseases-conditions/flu/expert-answers/flu-symptoms/faq-20057983
  9. https://www.cdc.gov/flu/treatment/treatment.htm
  10. https://www.mayoclinic.org/diseases-conditions/flu/diagnosis-treatment/drc-20351725
  11. https://doh.wa.gov/you-and-your-family/illness-and-disease-z/flu/are-you-high-risk-flu
  12. https://www.marshfieldclinic.org/specialties/primary-care/flu/flu-high-risk
  13. https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)
  14. https://www.nyp.org/medicalgroups/queens/for-patients/healthcare-articles/covid-19-vs-flu
  15. https://www.who.int/news-room/questions-and-answers/item/coronavirus-disease-covid-19-similarities-and-differences-with-influenza
  16. https://www.mayoclinic.org/diseases-conditions/coronavirus/in-depth/coronavirus-vs-flu/art-20490339
  17. https://www.prevention.va.gov/flu/prevention/index.asp
  18. https://www.bcm.edu/departments/molecular-virology-and-microbiology/emerging-infections-and-biodefense/specific-agents/influenza-virus-flu
  19. https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/influenza-virus