Flu (influenza)

Influenza, more popularly known as the flu, is a viral infection that affects the nose, throat, and lungs. It spreads easily from person to person and can cause symptoms ranging from mild to severe, including fever, cough, body aches, and tiredness. Most people recover within a couple of weeks, but the flu can sometimes lead to more serious illness, especially in young children, older adults, and people with certain health conditions.

Penn Medicine is a trusted provider of flu prevention and care, offering convenient access to clinics and practices across Pennsylvania and New Jersey.

Influenza symptoms tend to appear within two or three days after being exposed to the virus. The first sign is often a sudden fever, sometimes accompanied by chills and body aches. Other symptoms of the flu may include headache, sore throat, cough, runny or stuffy nose, and extreme tiredness.

Some people also lose their appetite, and children may have nausea, vomiting, or diarrhea. However, what people typically refer to as the “stomach flu” is usually viral gastroenteritis caused by other viruses, not influenza.

While fever often goes away within a few days, and most people recover within one to two weeks, coughing and fatigue may persist.

Influenza can sometimes cause complications, such as pneumonia, sinus infections, or worsening of chronic health problems like asthma. Anyone can get complications, but people at higher risk include young children, adults over 65, and people who are pregnant, have chronic diseases like diabetes or heart disease, or have weakened immune systems. Severe cases may require hospitalization and can even be life-threatening.

The influenza virus spreads when someone who has it coughs, sneezes, or talks, sending tiny droplets into the air that you breathe in. You can also catch the flu by touching a surface with the virus on it and then touching your mouth, nose, or eyes. People are usually contagious about one day before flu symptoms start, so you may spread it before you even know you’re sick.

Most people with flu symptoms don’t need a medical test or doctor’s visit. But if your symptoms are severe, or you’re at higher risk for complications, your provider may do a simple swab of your nose or throat to check for flu and may test for other infections, such as COVID-19. Rapid tests can give results within minutes and help guide treatment decisions, including whether antiviral medication may be appropriate. Testing can also be helpful in places where illness can spread quickly, like nursing homes, dorms, or shelters.

Most people with the flu can recover at home with rest, fluids, and over-the-counter medicines like acetaminophen or ibuprofen to reduce fever and body aches. Children should not take aspirin because of the increased risk of Reye syndrome, a rare but serious condition that causes swelling in the liver and brain.

In some cases, providers may prescribe antiviral medicines. These drugs don’t cure the flu, but they can shorten the duration and lower the chance of serious complications. They work best when started within two days of the first symptoms. Antibiotics don’t work against influenza because it’s caused by a virus, not bacteria.

The best way to prevent influenza is by getting a yearly flu shot. Everyone six months and older should get vaccinated, ideally before flu season begins. Flu vaccines are available by injection or nasal spray, depending on age and health. Penn Medicine makes prevention simple by offering flu vaccines at primary care practices and clinics throughout the region.

You can also lower your risk by washing your hands often, covering coughs and sneezes, and avoiding close contact with sick people. Help prevent the spread of flu and other infectious diseases by staying home if you’re sick. You can remain contagious for up to a week after getting sick, so take precautions to protect others even after you start feeling better. Cleaning high-touch surfaces and improving airflow in your home also help slow the spread.

At Penn Medicine, our experts provide complete care for influenza, from accurate diagnosis and effective flu treatment to advanced prevention strategies. Penn researchers also helped pioneer the mRNA technology that has shaped modern vaccines, demonstrating leadership in fighting infectious diseases.

Our primary care teams make it easy to get your annual flu shot. With access to the latest science, coordinated care, and patient education, Penn Medicine is a trusted partner in protecting your health during flu season and beyond.