When Does Flu Season Start? What to Know About Flu Seasons

Flu season sticks around for several months and it's a lot less fun than other seasons. Here's why there is a flu season, when it starts and ends, and how to avoid getting the flu during this time of peak illness.

Flu season and Covid-19

While the world’s attention is focused on Covid-19, it’s easy to forget the other deadly virus circulating right now: the flu virus or influenza. Flu season has just begun and while it’s impossible to know what toll it will take this fall and winter, the virus typically hospitalizes between 140,000 and 810,000 people each year and kills 12,000 to 61,000, according to the Centers for Disease Control and Prevention (CDC). A 2017 study in Clinical Infectious Diseases suggests that on average, 8 percent of the U.S. population fall ill with influenza annually.

“It’s not insignificant,” says Sandra Kemmerly, MD, system medical director of hospital quality at Ochsner Health in New Orleans. “The flu still remains a very serious disease and it’s still present.”

Here’s what you need to know about flu season, including when does flu season start, symptoms, diagnosis and treatment, flu symptoms vs Covid-19 symptoms, and where to get the flu shot.

What is the flu?

Influenza, or the flu, is a respiratory virus that can be passed between people or by touching contaminated surfaces. It can cause both mild and severe respiratory illness. The disease can be especially severe in high-risk groups like children younger than 5, adults over 65, and people with certain chronic medical conditions like asthma or diabetes.

Covid-19 is also a virus that can cause respiratory disease, but it is caused by a coronavirus, which makes it different from influenza. You can transmit both Covid-19 and the flu even before you have symptoms. (Know these 10 deadly flu signs.)

Symptoms of the flu

Flu symptoms usually come on suddenly and can include a fever, cough, sore throat, body aches, headache, and feeling tired, says Alexa Mieses Malchuk, MD, professor of family medicine at the University of North Carolina School of Medicine. You may also have a runny or stuffy nose.

Occasionally, people have vomiting and diarrhea as well, but that’s more frequent in children. If your main symptoms are gastrointestinal, it’s probably not influenza and more likely a stomach bug, such as norovirus, or something else. Many of these can also be Covid-19 symptoms.

The flu usually only progresses to severe disease in a small minority of cases, says Dr. Kemmerly. Many more people with Covid-19 get so sick that they need to be hospitalized and sometimes intubated. (Learn more about Covid-19 symptoms vs. flu symptoms.)

Woman on couch checking temperaturePixelsEffect/Getty Images

Diagnosis and treatment

Because common colds, Covid-19, and other illnesses can seem so much alike, it’s virtually impossible to diagnose the flu without an actual lab test. And because the treatments for Covid-19 and influenza are different, it’s important to be able to distinguish between them.

“We would like to identify which one of the viruses is causing somebody to be sick because treatments are not interchangeable,” says Dr. Kemmerly.

Several antiviral drugs are approved to treat the flu. These haven’t proved effective against Covid-19, but there are other promising Covid-19 drugs, including the steroid dexamethasone and the antiviral drug remdesivir, which seem to work for some patients.

The flu and Covid-19

Although these are caused by two completely different viruses, experts are concerned that people could get sick with both at the same time.

“It is possible to be infected with both the flu and Covid-19. It is also possible to become sick with one disease while recovering from the other,” says Dr. Mieses Malchuk. “The result could be life-threatening.”

It could also overwhelm a health care system that is already straining at the seams. The best thing you can do is get a flu vaccine—more on this later.

When does flu season start?

The timing is a little different each year, but typically flu season in North America starts in early October and peaks between December and February, although cases are sometimes seen as far out as May, according to the CDC.

In the Southern Hemisphere, the flu also strikes in the fall and winter which, there, is April through September. (Here’s what not to do during flu season.)

Why is the flu seasonal? “Temperature is a factor with influenza and the number of people congregating together inside makes influenza more transmissible,” says Dr. Kemmerly. Covid-19 has turned out to be less tied to seasons.

Get your flu vaccine now

Each flu season brings different strains of the flu and also different types of vaccines, including the flu shot (the most common) and a vaccine nasal spray (FluMist). It’s important to talk with your doctor to decide which one is best for you.

“The flu vaccine changes every year in an attempt to protect us from the strain with which we are most likely to become infected,” says Dr. Mieses Malchuk. “Some years are better than others in terms of vaccine effectiveness but all flu vaccines help us have less severe symptoms.”

The flu vaccine isn’t as effective as the new Covid-19 vaccine, which is estimated to have a 95 percent efficacy rate after the second dose, according to a BMJ study released this month. Flu vaccine effectiveness ranges from 40 percent to 60 percent, but it’s still the best way to prevent flu and to fend off severe illness. There’s also an additive effect.

“Repeated vaccination offers protection,” says Dr. Kemmerly. And while the best time to get vaccinated is in early October, it’s absolutely never too late, she adds.

Here’s how to find a flu shot near you and nationwide pharmacy and store chains where you can get your flu shot:


Amanda Gardner
Amanda Gardner is a freelance health reporter whose stories have appeared in cnn.com, health.com, cnn.com, WebMD, HealthDay, Self Magazine, the New York Daily News, Teachers & Writers Magazine, the Foreign Service Journal, AmeriQuests (Vanderbilt University) and others. In 2009, she served as writer-in-residence at the University of Wisconsin School of Medicine and Public Health. She is also a community artist and recipient or partner in five National Endowment for the Arts grants.