How Does the Flu Virus Work? A Friendly Explanation

The flu virus hijacks your cells to replicate, spreads through droplets, and mutates rapidly, causing yearly outbreaks. Discover how the flu virus works in this informative guide.

The flu, short for influenza (in-floo-en-zuh), is a virus that spreads easily. It can lead to sickness from mild to very severe. Sometimes it can even be deadly for both healthy children and adults.1 You can pick up the flu when someone near you coughs or sneezes. It’s also possible to get it by touching something that has the virus on it and then touching your face.2 Surprisingly, you can pass the flu to others before you even feel sick. And you could keep spreading it for over a week after you start to show symptoms.

Key Takeaways

  • Influenza is a highly contagious viral infection that can cause severe illness and complications.
  • The flu virus spreads primarily through coughing, sneezing, and contact with contaminated surfaces.
  • Individuals can transmit the flu virus to others before and after experiencing symptoms.
  • The flu virus undergoes rapid mutation, making it challenging to predict and prevent.
  • Annual vaccination is the best way to protect against the flu and mitigate its impact.

Introduction to the Flu Virus

The flu, short for influenza, is a contagious infection causing many in the U.S. to get sick each year. It can lead to hospital stays or, unfortunately, even death.34 It’s vital to know about the flu’s nature and harm to fight it effectively.

Understanding Influenza: A Contagious Viral Infection

The flu spreads easily, especially through coughing, sneezing, and close contact. What’s tricky is that it can spread before symptoms show up or even after someone starts feeling better.3 This makes it crucial to prevent the flu from spreading to others.

The Burden of Flu: Illnesses, Hospitalizations, and Deaths

The flu season can hit the U.S. hard, with many people getting sick and needing medical care. Take the 2022-2023 season, for instance, where there were millions of illnesses, hospital stays, and sadly, thousands of deaths.3 This disease also brings a big financial cost, spending over $11 billion a year.4 Therefore, it’s extremely important to have strong plans in place against the flu.

Symptoms of the Flu

The flu isn’t just a common cold. It hits you fast. Those with the flu might have fever, aches, chills, and feel very tired.

They also might have a cough, runny or stuffy nose, or sore throat.5 Children may vomit and have diarrhea more than adults.

Fever, Aches, Chills, and Tiredness

The flu often brings on a high fever and makes your muscles and body hurt. You might get headaches and feel extremely tired too.

These symptoms can last a few days. They are usually more intense than a cold.5

Cough, Runny Nose, and Sore Throat

Flu can give you a lasting cough, a nose that won’t stop running, and a sore throat. These symptoms may stick around for a while.5

How the Flu Virus Spreads

Influenza viruses mostly spread when sick people cough or sneeze.3 You can also catch it by touching something with the virus on it.3 Then, if you touch your mouth, eyes, or nose, you might get infected.3 Before someone even shows symptoms, they could spread the flu. They might continue spreading it for over a week after feeling sick.3

Coughing and Sneezing: The Primary Transmission Route

When someone with the flu coughs, sneezes, or talks, they shoot out tiny droplets.6 These droplets might land in the mouth or nose of someone nearby. Or, they could be breathed in, reaching the lungs.6

Surfaces and Hand-to-Face Contact

If a person touches a contaminated surface and then their face, they might get the flu.3 This way of spreading the virus is not as common. Yet, it’s still a possible means of transmission.6

Flu Transmission ModesKey Statistics
Coughing and Sneezing
  • Flu viruses spread mainly through respiratory droplets when people cough, sneeze, or talk.6
  • Most healthy children and adults with the flu can infect others starting about one day before showing symptoms and up to seven days after symptoms resolve.6
  • People with weakened immune systems can remain contagious for up to several weeks.6
Touching Contaminated Surfaces
  • Influenza viruses may also spread when a person touches a surface or object that has the virus on it and then touches their own mouth, eyes, or nose.3
  • This is a less common way for flu to spread, but it can happen.6

flu transmission

The Structure of the Influenza Virus

The flu virus, or influenza virus, is a pretty complex thing. It’s key in how flu spreads and makes people sick. Knowing its details is vital for stopping the flu.

Influenza virions are its tiny particles. They’re about 80 to 120 nanometers big, with round or egg-like shapes.7 The virus has a covering made from the cells it attacks. This covering has two spikes made from proteins: hemagglutinin (H) and neuraminidase (N).7 These spikes help the virus stick to cells, get in, and then leave them.

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The flu’s genetic material is in eight single strands of RNA. This divided setup makes the flu change quickly by mixing its genes with other flu viruses.7 This is how new flu types appear, ones that we might not be ready to fight off yet, causing outbreaks.

The flu changes slowly and also in sudden big steps. Slow changes are called antigenic drift, where parts of the virus mutate over time. A sudden big change is antigenic shift. This can create a new and more dangerous flu type.7

The way the flu virus is built and changes makes it hard to deal with. Keeping an eye on it and studying it is very important. This helps in making better vaccines and medicines. These can fight the flu better and keep us healthier.

How Does the Flu Virus Work?

Hijacking Host Cells for Replication

Influenza viruses easily pass from one person to another when someone coughs or sneezes.4 They can also spread if you touch a surface with the virus and then your face.4 People can spread the flu before they feel sick and up to a week after they get sick.4 The virus spreads mainly through droplets from coughing, sneezing, or talking.

Rapid Mutation and Yearly Outbreaks

The flu virus changes often, which is why you need a new vaccine each year.8 In the U.S., the Centers for Disease Control and Prevention say that millions get the flu yearly.8 With a virus potency marker of 1.5, an infected person usually spreads it to fewer than two people.8

Prevention: The Importance of Flu Vaccination

Getting a flu shot every year is the top way to avoid the flu.9 The CDC says all people 6 months or older should do this.9 Aim to get it in the fall. This is before the flu starts spreading around. Yet, it helps to get your shot anytime during flu season.9

CDC Recommendations for Annual Flu Shots

9 Each year, new flu shots come out. They help fight the flu types most likely to be around. Though not a 100% shield, they cut down on how bad the flu hits you.10

Benefits of Flu Vaccination

10 Flu shots lower your chances of catching the flu by 40% to 60% when the vaccine matches well.10 They are better at fighting some strains like B and H1N1 than others.10 The vaccine kept many from getting the flu, visiting the doctor, or going to the hospital in the 2019-2020 season.10 It also cut flu deaths and serious injuries, like ICU trips, for those who did get sick.10

10 Over time, flu vaccinations have saved many people, especially kids and those with health issues.10 They’ve even lessened the number of children who ended up in the ICU or passed away from the flu.10 Pregnant women had a much lower rate of flu hospitalizations when they got their flu shot.10

10 A study in 2022 showed a big drop in severe flu cases among kids who were vaccinated.10 The 2018-2019 season saw many fewer hospital visits and less severe cases for children from the vaccine.10 It’s a huge help in keeping kids from the worst outcomes of the flu.

10 Sometimes, the flu shot is not as effective, especially against certain types of the flu.10 Yet, it remains the best defense we have.10 Its power to protect lessens as people get older, but it’s still very important for everyone to get it.10

Influenza Mutations and Avian Flu Threats

The influenza virus keeps changing, making it hard to stop its spread. A recent case in a worker from Michigan showed a new mutation. This change helps the virus infect mammals better.11 The ECDC warns that bird flu could soon spread to humans more easily.11

H5N1 Bird Flu: A Global Concern

Since 2022, the H5N1 bird flu has killed millions of birds. It recently spread to minks in Spain, leading to 50,000 of them being culled.11 Bird flu cases in people are appearing in the US, Australia, and South-East Asia. This is worrying health experts, especially as the virus moves into new animals.11 For now, it can’t pass from person to person, but there are concerns. If farm animals get the virus, they might pass it to us because of how often we interact with them.11

Monitoring and Preparedness Efforts

Right now, the WHO says the danger of bird flu to us is small.11 But it’s preparing for the next big flu pandemic. This could be caused by the bird flu or something else.11 There’s a plan to make vaccines for bird flu just in case it starts spreading between people. The first vaccines could be ready within four months of a pandemic being declared.11

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Treatment: Antiviral Medications and Their Role

Getting a flu shot every year is the top way to avoid the flu. Antiviral drugs are not a replacement for this. But, they are another important tool in fighting the flu. CDC says if you’re hospitalized, very sick, or at high risk, you should get antiviral meds right away if you might have the flu.

Reducing Symptoms and Preventing Complications

Antiviral drugs help make flu symptoms lighter and cut the sick time by one to two days. They also stop serious problems like pneumonia.12

Timing and Effectiveness of Antivirals

The best time to start antivirals is within 48 hours of feeling sick. But they can still help a bit if you start later.1213 Doctors can give oral oseltamivir phosphate to people 14 and up, two days from when their symptoms started. And kids as young as 1 can even use it to help not get the flu.13

Intravenous peramivir is for ages 6 months and up, also within 2 days of becoming sick.13 For those 5 and older, there’s oral baloxavir, with a stronger option for high-risk 12-year-olds.13 It helps people with flu B get better a whole day sooner than with oseltamivir.13 Baloxavir was just okayed for kids 5 to under 11 in August 2022, within 2 days of symptom start.13 Yet, mixing oseltamivir and baloxavir doesn’t work better than just oseltamivir for kids age 12 and up in the hospital.13 If you get baloxavir within 48 hours after being around someone with the flu, it cuts your chance of getting it by 86%, if you’re 12 or older.13

Still, the best way to guard against the flu is a yearly flu shot.12 Antivirals are a big help, though, especially for those most at risk.12Using the right antiviral quickly can add an extra layer of defense.

Flu Prevention at School and Work

To fend off the flu at school and work, it’s key to learn about safety steps.14 Schools and workplaces use non-drug actions to keep flu at bay. They clean often, keep sick people apart, and encourage good hygiene.14 At the office, this includes regular cleaning, having enough hygiene stuff, and making sure others can step in if needed.14

School and Childcare Preparedness Plans

Ask if your child’s place has a flu plan and if they offer vaccines there.14 They should clean and have hygiene stuff ready, like tissues and soap. Also, check if they care about air quality.14 Find out how they handle sick people and who looks after them until they can leave. Know their policy for absentees too.14

Workplace Hygiene and Absentee Policies

Know if your job is ready for flu season and offers flu shots.14 Clean places you touch a lot to stop germs.14 Ensure there’s enough stuff for hygiene. Teach others your job in case you’re out sick.14 Leave work ASAP if you start feeling unwell.

Nonpharmaceutical Interventions (NPIs)

Annual flu shots and antiviral drugs are vital for flu prevention. Nonpharmaceutical interventions (NPIs) are also key.15 They include measures that aim to stop disease spread without using drugs or vaccines. These efforts change how people act and their surroundings.15

Avoiding Close Contact and Staying Home When Sick

Stay away from sick people and stay home if you’re the one feeling ill. Keeping a distance prevents the virus from spreading.16 Plus, staying home when sick keeps others safe. Wait until you feel better and are fever-free for 24 hours before mingling again.16

Cough Etiquette and Hand Hygiene

Always cover your mouth and nose when you cough or sneeze. It’s a simple way to protect those around you. Consider wearing a mask to guard yourself and others. Masks worn by the sick help stop virus spread. They also block the sick from breathing in harmful particles.15

Keep your hands clean to avoid picking up germs. Frequent handwashing is best. Use a hand sanitizer if soap and water aren’t around.15

Cleaner Air and Surface Disinfection

Improving indoor air by letting fresh air in helps reduce the chance of viruses.15 Also, cleaning things like handrails and doorknobs often stops illness spread.15

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Flu Awareness and Educational Resources

The CDC offers lots of flu education, flu awareness, and flu resources.14 There are “Cover Your Cough” flyers and posters in many languages. You can also find online videos and tools. These help people and groups learn how to fight the flu.

CDC Materials and Printable Posters

There are many printable resources from the CDC. These include “Cover Your Cough” materials in different languages.14 They aim to teach the public about preventing flu spread through coughing right and keeping hands clean.

Online Videos and Interactive Tools

Besides printouts, the CDC has a variety of online videos and tools. They cover flu education and flu awareness in more detail.14 These online aids inform people about the flu, its spreading, and ways to stay safe.

Flu and Respiratory Illness Preparedness

Preparing for flu and other illnesses protects everyone. Being proactive can lessen the virus’s impact.14

Individual and Community Readiness

Getting a flu shot every year is vital. Also, stay away from sick people, and stay home if you’re sick.14

It’s important to cover your cough and wash your hands often. These simple steps help keep everyone safe. They stop the flu and other diseases from spreading.14

Vaccination and Healthy Habits

Fighting the flu starts with a yearly vaccine. This keeps you and your family safe.14

Good habits, like clean hands and coughing into your elbow, also help. These lower the chance of getting or spreading diseases.14

By doing these things, you help your community. You make it stronger against the flu and other sicknesses.14

Staying ready and informed is key. Tips and info can help us stay well.14

Together, we can beat the flu. Let’s protect our families and society from its harm.1417


The flu virus spreads easily and can make people very sick. It not only affects our health but also our money and the way we live.18 Knowing about the influenza virus helps us fight it better. This includes learning how it looks, how it grows, and how it changes quickly.19 To fight the flu, we should get our flu shot every year. We can also use antiviral drugs. Besides, we should keep clean and keep our distance from sick people. And, it’s important for everyone to watch for signs of the flu and be ready to act.20 Being aware and taking steps to prevent the flu can lessen its impact on us and those around us.


What is the flu virus?

Flu, short for influenza, is a contagious virus that spreads easily. It causes mild to severe symptoms and can be dangerous. This includes the risk of death, especially for children and the elderly.

How does the flu virus spread?

Flu viruses spread when an infected person coughs or sneezes near others. It can also spread by touching a surface with the virus and then touching your face. This means the flu can be caught before symptoms appear and up to a week after they start.

What are the symptoms of the flu?

Flu hits fast, leaving people suddenly sick. Symptoms include fever, body aches, chills, fatigue, cough, and a sore throat. Children might also have vomiting and diarrhea more than adults.

How can the flu be prevented?

Getting a flu shot every year is the best way to avoid the flu. The CDC recommends this for everyone aged 6 months and older. The vaccine changes each year to fight the viruses expected to spread the most.

How is the flu treated?

Remember, a flu vaccine can help more than treatment. But for those at risk of serious complications, like the elderly or hospitalized patients, antiviral medications can help. These should be used as soon as the flu is suspected.

What is the impact of the flu?

The flu affects millions in the US. It leads to hundreds of thousands of hospitalizations and tens of thousands of deaths. This is not just a health issue but also affects the economy, costing billions each year.

What is the current threat of avian influenza (H5N1 bird flu)?

H5N1 bird flu is spreading among wild birds globally, affecting poultry and some US dairy cows. Though the risk to humans is low now, the CDC is watching closely and updating as needed.

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