Flu Season: A Timeline for the Start, Peak and End

When late summer days start to give way to cool autumn nights, flu season is just around the corner. Influenza, aka the flu, is a common viral infection that can cause serious complications.

So, what exactly is flu season, and when does it start?

Primary care physician Charles Garven, MD, explains.

What is flu season?

Spring, summer, winter, fall and … flu season? OK, OK, it’s not one of the official seasons of the year, but it’s certainly one worth knowing. This term refers to the time of year when cases of influenza rise dramatically.

“You can come down with the flu any time of year,” Dr. Garven clarifies. “But it’s much more common during the cold-weather months.”

Flu season is also sometimes known as “respiratory season” because influenza isn’t the only condition that tends to peak during this time. It’s also a key time for other respiratory illnesses, ranging from sinus infections and the common cold to more severe conditions, like RSV and pneumonia.

And while there’s no tried-and-true way to know how bad flu season will be during any given year, there are some clues. To get an idea of how heavy or light flu season will be in North America, infectious disease experts look at what’s happening elsewhere.

“Australia is basically a season ahead of us when it comes to the flu,” Dr. Garven explains. “So, when we see what their flu season looks like, that’s often a predictor of what we may be able to expect here.”

How long does flu season last?

Flu season is usually thought to last from September to May, with cases peaking in deep winter. But that’s not necessarily always the case.

Dr. Garven provides a timeline for flu season, including when cases usually rise and fall.

Fall and early winter: Flu season begins

October is considered the start of flu season, but cases are usually low during this time of year.

“The flu kind of creeps slowly onto the scene,” Dr. Garven says. “We start to see it in early fall, and then cases begin ramping up as we get deeper into the season.”

December to February: Flu season peaks

The coldest months of the year are considered peak flu season, with the U.S. Centers for Disease Control and Prevention (CDC) reporting that February is historically the worst month for the flu. But, again, that’s not always the case.

“Data that looked at 40 years’ worth of flu seasons showed February was the peak month most often,” Dr. Garven notes. “But there have been years when the high point of flu activity has occurred as early as December and as late as March.”

Early spring: Flu season ends (but doesn’t disappear)

So, when does flu season actually end? Cases often start to wind down by March, with very low numbers being reported by May.

“The virus doesn’t always follow a predictable schedule, which means there’s no definitive finale,” Dr. Garven says. “But most years, it tends to wind down as the weather warms up, with cases slowing in early spring.”

Want more of-the-moment information? During flu season, the CDC’s FluView tool provides ongoing data about cases of the flu. You can dig deep into statistics, if that’s your thing — or keep it simple and look for the note at the top of the page that says whether seasonal influenza activity is currently high or low.

Preventing flu during flu season

There are many ways to reduce your risk of coming down with the flu, from maintaining good handwashing hygiene and disinfecting surfaces to focusing on ways to boost your immune health.

But the No. 1 best way to prevent the flu is to get your flu shot — and to do it every year. That’s because there are many different strains of the flu, and the virus can change, or mutate, quickly.

“The flu we experienced last year may not be the one we see this year, and this year’s flu may not be the one we face next year,” explains Dr. Garven. “So, getting an annual shot is key to protecting yourself and your family.”

Studies continue to show that getting the flu vaccine significantly lowers your chances of getting the virus. And if you do get it, you’re less likely to become seriously ill as a result.

When should you get your vaccines?

It’s best to get the flu shot in September or October so you’re protected once flu season kicks into high gear. But if you’re reading this in November or later, there’s still time.

“It’s really never too late into flu season to get the flu shot,” Dr. Garven encourages. “If you didn’t get it in early fall, it’s absolutely still worth doing it now. It can help keep you protected during flu season, no matter when this year’s peak may be.”