As the calendar flips later in the year, it seems like coughing and sneezing begin like clockwork — but it’s not the date that dictates flu season, it’s actually the humidity.

Scientists have long known that climate plays a role in the spread of the flu, but the details of exactly how factors like humidity could predict outbreaks has remained unclear, until now.

The intertwined relationship

As I’m sure you’re all too familiar with, flu season in the U.S. usually peaks in the late fall and winter months. 

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Meanwhile, in the tropics, flu outbreaks can happen year-round, often coming with multiple spikes.

So, how can some places see surges in the flu during their coldest months while others see it throughout their ever-present warmth?

A study led by researchers at Brown University found that the flu can spread more easily in both very dry climates and very humid ones.

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This explains why we see surges in flu cases in locations with cold, dry winters, like parts of the U.S. for example, as well as increased transmission throughout the year in more tropical, humid environments. 

And while other factors like vaccination rates, population density and human behavior also impact the spread of the flu, it's fascinating that forecasting the weather can help with forecasting flu outbreaks. 

This brings us to another important thing to consider: As our climate changes, this means our flu season will change too.

Changing climate, changing flu season

With these findings in mind, combined with the models for our warming planet, there are predicted shifts coming to the sniffling, sneezing season.

Places that experience colder winters could see milder flu seasons as the world warms.

However, tropical regions could see stronger flu outbreaks and the timing of the peaks could shift as well.

While there is still more research to be done here, it is obvious that as our climate continues to change, there will be a ripple effect into other areas of our lives, including when we could get sick.

How can you protect yourself no matter the weather?

September and October are the prime months to get your flu shot to help protect yourself throughout the season.

Seem a little early? That’s because the antibodies take around two weeks to develop and help fight off the flu.

This year’s vaccine includes three different strains, two for Flu-A and one for Flu-B. 

And while the vaccine acts as a proactive measure, you can still catch the virus, so remember to avoid touching your eyes and mouth, wash your hands frequently and stay home if you’re feeling sick.

Caitlin Kaiser graduated from the Georgia Institute of Technology with both an undergraduate and graduate degree in Earth and Atmospheric Sciences before starting her career as a digital meteorologist with weather.com.