Let’s Talk About the Flu

We've got the doctor-approved scoop on flu causes, symptoms, treatments, and a ton of other facts and tips that can make life with influenza easier.

Whether you’re currently fighting off the flu or you’re hoping to dodge it this season, you’re in the right place. Some people experience only mild flu symptoms, but it can pack a real punch for others. There are things you can do at home to feel better, including taking medications, that can help you recover faster and with fewer issues. The flu might seem like old news but remember: Flu strains change every year. If you’ve got questions, we’ve got the answers to all the flu facts you need to know.

Flu (Influenza)

Our Pro Panel

We went to some of the nation’s top influenza experts to bring you the most scientific and up-to-date information possible.

Amesh A. Adalja, M.D.

Amesh A. Adalja, M.D.

Internist specializing in infectious diseases and critical care

University of Pittsburgh Medical Center

Pittsburgh, PA

Frank Esper, M.D. headshot.

Frank Esper, M.D.

Infectious disease specialist

Cleveland Clinic

Cleveland, OH

Michael L. Jackson, Ph.D. headshot.

Michael L. Jackson, Ph.D.

Senior investigator

Kaiser Permanente Washington Health Research Institute

Seattle, WA

Flu (Influenza)
Frequently Asked Questions
How do I know if it’s the flu?

Flu symptoms are extremely similar to other respiratory viruses. Mild flu can sometimes feel like just a cold, and severe flu can closely match COVID-19 symptoms. The only way to know for sure is to get tested at your doctor’s office or a clinic.

Can I treat the flu at home?

Treating flu means treating the symptoms: If you have a fever, take over-the-counter fever reducers like acetaminophen or ibuprofen. Aches and pains can also be treated with pain relievers. And there really is something to the old adage about chicken soup—it provides needed fluids and soothes a sore throat, plus inhaling the broth can open up your nasal passages to ease your breathing.

When should I seek medical attention for flu symptoms?

Seek urgent medical care if you have flu with any shortness of breath, any new or worsening heart issues, a fever that won’t come down, or if you can’t perform your activities of daily living, like eating or getting dressed, due to overwhelming fatigue.

How contagious is the flu?

It’s not as contagious as COVID-19, but it’s on par with other respiratory viruses, including the common cold. As long as you have a fever, runny nose, or cough, you should consider yourself contagious. If you have to be out of the house while you have symptoms, wear a mask to reduce the chance you’ll spread the virus to others.

What Is the Flu, Anyway?

Imagine someone tucked under a pile of blankets on the couch, red nose, box of tissues at hand, and a thermometer sticking out of their mouth. What’s your first thought? Though our world has been focused on COVID-19 most recently, the flu, another type of respiratory infection caused by viruses, is just as likely to be the culprit, affecting between 9.3 million to 45 million Americans yearly, depending on the flu season, according to estimate from the Centers for Disease Control and Prevention (CDC). Moreover, since 2010, there have been between 12,000-61,000 flu deaths and 140,000-810,000 hospitalizations from flu each year.

Both men and women can get the flu, as can people of any age. The flu season keeps researchers on their toes each year—different strains vie for the highest infection rates, and where the flu hits geographically shifts unpredictably.

Flu season can vary, but it typically runs from November to March. In some years, it can extend from October all the way to May. The calendar can help you determine when to get vaccinated, when to ramp up flu prevention strategies, and how to figure out if, despite your best efforts, you caught the flu or could possibly have something else.

Types of the Flu

Several influenza viruses circulate around the world each year—influenza A, B, C, and D. Not all of them can infect people—some target other mammals or birds. The vast majority of human cases are caused by influenza A.

  • Influenza A: Influenza A viruses are characterized by their combinations of proteins: “H” hemagglutinin proteins have 18 subtypes and “N” neuraminidase proteins have 11, so you can have an H1N1 influenza A virus, an H3N2 influenza A virus, or several other combinations. Influenza A is the leading cause of the annual flu season.

  • Influenza B: There are two main lineages—influenza B Victoria and influenza B Yamagata—and differentiating strains within each. Though not as prevalent as A, influence B may also contribute to the flu season.

  • Influenza C: This usually causes only a mild illness.

  • Influenza D: This virus mostly infects cattle and isn’t known at this time to cause illness in humans.

What sets influenza viruses apart is the rate at which they mutate. Influenza A viruses change more rapidly than influenza B ones. These changes are slight, but enough so that our immune system doesn’t recognize the new versions enough to fight them off effectively from year to year. This explains why we need an annual flu shot, uniquely formulated to fight each year’s anticipated strains.

What Are the Symptoms of the Flu?

It can be tough to tell if your symptoms are from the flu, a cold, or another type of infection (hello, COVID). Though there’s definitely overlap in terms of virus symptoms, the flu does have some telltale signs that distinguish it from a cold, especially when it’s severe, like fever, cough, muscle aches, and pain. If you have a respiratory illness that came on slowly and isn’t accompanied by a fever or headaches, it might just be a cold and not the flu.

When it comes to telling COVID-19 and the flu apart, it’s a tougher call. The symptoms of the flu and COVID-19 are remarkably similar. Because of this, it’s becoming more common for providers to test patients for flu at the same time they get tested for COVID-19 if they’re showing symptoms. There’s even a test that can check for both, called Flu SC2, but it’s solely for use in state public health laboratories for now.

Common Flu Symptoms

Flu symptoms can feel like they came out of nowhere. You may have all these, or just a few. The most common symptoms are:

  • Fever. A temperature of 100.4℉ is technically a fever, but the flu tends to send those numbers higher, to around 102 or 103℉.

  • Chills

  • Headache

  • Sore muscles or body aches

  • Feeling extra tired or fatigued

  • A dry cough

An important note: Even though fever is very common, not everyone will experience it.

Less Common Flu Symptoms

Other symptoms are less common:

  • Sore throat

  • Stuffy nose

  • Sneezing

Sometimes you can add gastrointestinal (GI) symptoms like vomiting or diarrhea to this list of maladies, though they’re much more common with kids who have the flu.

And what about the “stomach flu”? That’s actually a misnomer and not connected to influenza at all—it’s just a shorthand way of saying gastroenteritis, which is caused by a virus, bacteria, or parasites. The way to know the difference is that its main symptoms aren’t respiratory, but rather GI-focused with diarrhea, abdominal pain, and vomiting prevailing.

What Causes the Flu?

The various flu viruses infect us through tiny droplets that are sprayed when people cough, sneeze, or talk. When these droplets land in another person’s mouth or nose, they’ve found themselves a new home. They may also land on a surface and stay long enough (a few hours max) to get picked up by someone who touches the surface and then touches their mouth, nose, or eyes, but that’s less common. Given the short lifespan of a virus, high-touch places like a cell phone, doorknob, or keyboard are the most likely contact points.

The flu virus itself, whether A or B, has specific proteins with distinct tasks—some bond to the cells that line the inside of your nose, throat, or lungs in search of a hospitable place to replicate, while others keep the virus strong and intact. Once the virus attaches to cells lining your respiratory tract, they cause the inflammation and irritation that lead to the host of flu symptoms.

Flu Risk Factors

There’s not much that makes an otherwise healthy person more likely to contract the flu than their best bud or co-worker, except perhaps if you’re in constant contact with a lot of people during flu season, as are healthcare workers and teachers, for instance. The more people you come into contact with, the greater the odds of coming into contact with their respiratory droplets.

No group is exempt from possibly contracting the flu at some point in their lives, but that doesn’t mean the virus affects everyone equally. While one person might have such mild symptoms that they mistake the flu for a cold, others can end up hospitalized. That risk of experiencing more severe complications from the flu is higher if you belong to one of these higher-risk groups:

People Over Age 65

Our immune systems weaken as we get older, and that’s one reason why people age 65 and up tend to be hit hardest by seasonal flu. The vast majority of flu-related deaths—about 70% to 85%—occur in those over age 65. They account for most flu-related hospitalizations, too (between 50% and 70%). Hospitalizations and deaths aren’t necessarily from the flu alone, but can be from related issues, from sinus or ear infections to pneumonia and even inflammation in the heart or brain.

Adults With Chronic Conditions

If you already have a chronic health condition, the flu could make it worse—either due to the way your immune response affects other systems in your body or because your condition makes a certain organ or system especially vulnerable to issues. Since flu is a respiratory virus, if you have asthma, for example, it could make asthma symptoms worse or lead to asthma attacks.

Heart disease or a history of stroke puts you at higher risk for flu complications due to the stress an infection can put on your circulatory system, such as inflammation, lowering the oxygen level in your blood, or lowering your blood pressure. In fact, a 2018 study found that the risk of having a heart attack was up to six times higher within a week of diagnosed flu infection than under everyday circumstances, particularly among people with underlying health factors like high blood pressure or diabetes.

If you have diabetes, even if it’s well-controlled, the flu can present some serious issues. That’s because diabetes can affect how well your immune system works, making it harder to fight off the flu. Getting the flu can make it harder to control blood sugar. The hormones that your immune system sends out to fight the infection also may raise your blood sugar, or your blood sugar level may drop due to a lack of appetite. Having diabetes also puts you at higher risk for developing other infections that can stem from the flu, like pneumonia, bronchitis, sinus infections, and ear infections. Similarly, since chronic kidney disease (CKD) can weaken your immune system, people with CKD are more likely to have severe flu or flu complications.

Children and Pregnant Women

Pregnant women, women in the two weeks following childbirth, and children under two years of age are other groups at high-risk for flu complications due to immune system changes in pregnancy and immune system fragility in young children, especially those who haven’t gotten vaccinated against the flu yet. A 2020 study found that women who contracted the flu during pregnancy had a higher risk of pregnancy loss and a higher risk of having a baby with a low birthweight.

Though adults can typically recover from flu at home, it’s common for children to need medical care. Young children with the flu can develop pneumonia, become dehydrated, get sinus or ear problems, or even experience brain dysfunction. To prevent severe flu and complications, children can start getting the flu shot after they’re six months old. The majority of flu-related deaths in children occur in those who haven’t been vaccinated.

How Is the Flu Diagnosed?

Your doctor may ask you a lot of questions when you come in feeling under the weather, but without a diagnostic test, it’s impossible to confirm whether the reason for your fever, cough, or aches is the flu—and that’s important because it will determine your course of treatment. The earlier flu is treated, the more quickly symptoms may improve.

Most flu tests use a swab to take cells from inside your nose or the back of your throat. Sometimes, saline might be sprayed into your nose and suctioned out to capture cells. The cells are then checked for the virus.

Commonly used “rapid tests” can show results as fast as 10 minutes, while you’re still at the doctor’s office. However, those tests tend to be more accurate in children than in adults and can sometimes give an inaccurate result. Other types of tests, which are typically more accurate, need to be sent out to a lab. Those results can take a few hours.

Since flu and COVID-19 have such similar symptoms, your doctor may opt to use a test that checks for both viruses at the same time.

Flu Treatment Options

Most people who have mild flu symptoms recover at home, and treatment tends to be focused on relieving the fever that typically accompanies the infection. If you’re managing flu recovery at home, you should:

  • Rest.

  • Drink plenty of water and other fluids to prevent dehydration.

  • Treat your fever or aches and pains with over-the-counter medications, such as acetaminophen or ibuprofen, whatever has worked best for you in the past. Take only as directed—some formulas are meant to last for 4 hours, others up to 8.

  • Avoid alcohol, which can lead to dehydration.

  • Avoid smoking, which can irritate your lungs further.

Though you might feel ill for a week or even two, once your fever breaks, you’ll be on the road to recovery.

If you had a flu test that came back positive, your doctor may prescribe an antiviral medication such as Tamiflu that can lessen your symptoms, decrease the time you’re sick, and potentially prevent serious complications. However, these drugs tend to work best when given within two days of symptom onset, so if you delay seeing your doctor, you may no longer be a candidate.

If you’re at high risk for flu complications due to your age, a chronic health condition, or a weakened immune system and are treating your flu symptoms at home, know the warning signs for when to call your doctor or seek urgent medical care. These include difficulty breathing, new or worsening heart problems, and a fever that won’t go down.

Though the world is focused on COVID-19, research to better understand the flu continues. The most pressing challenge is to develop a universal flu vaccine that wouldn’t need updating every year. Until then, have a plan in place should the flu come to your house.

Can You Prevent the Flu?

The best way to try to prevent the flu from getting a foothold is with a flu vaccine. Get your yearly flu shot, ideally in October, though the start of the flu season changes a bit from year to year. Even if your only chance to get it is in February or March, at the tail end of the season, it’s still better than not getting one at all.

How effective a flu vaccine is at reducing illness in a population changes from year to year as researchers in one hemisphere look to the mutations in the opposite hemisphere to predict how to formulate a vaccine for maximum protection. A rough benchmark for the annual flu shot is that it’s 40-60% effective, meaning the goal is for a 40-60% reduction in the amount of people who become ill, as compared to a population without the vaccine. But even if you get the flu shot and still get sick, you’re less likely to have to go to your doctor’s office or a hospital for care. Unfortunately, the flu will likely always be with us. The goal of the flu shot is not only to reduce infections, but also to keep infections that do evade the vaccine mild enough that you can recover at home.

In addition to the vaccine, wearing a mask makes a difference—a silver lining to masking up for COVID-19 protection was a sharp drop in flu cases reported to the CDC...by close to an astounding 99%.

Danielle Oaks
Meet Our Writer
Danielle Oaks

Danielle Oaks is a health writer and editor with a background in health communications, public health, and medical interpreting. She has worked for HealthDay, among other health organizations.