We're well into the new year, but flu season isn't over.

"I don't think we've reached the peak yet," says Emily Shuman, M.D., an assistant professor of internal medicine and an infectious disease specialist at Michigan Medicine.

MORE FROM MICHIGAN: Sign up for our weekly newsletter

She's probably right: The U.S. Centers for Disease Control and Prevention reported just at the end of January that the flu had become widespread in most of the United States. Flu-related hospitalizations are continuing to rise, CDC data show.

Although the flu's arrival and exit vary slightly each year — the 2016 outbreak lasted well into the spring, Shuman says — flu season generally peaks during January and February.

That's because we're cooped up indoors during the dark and chilly months, allowing an easier exchange of germs. The onset of colder, drier air is also thought to play a role; studies have shown flu germs survive longer when humidity drops.

Thanks to these factors and others, the virus' origins and life cycles repeat predictably: Most flu strains originate in Asia and the Southern Hemisphere, where flu season occurs in their winter, Shuman says. And each year the transmission mechanics remain the same.

Shuman explains when you're most at risk:

What to do if you catch the flu

Although most people never plan to get sick, it's crucial to stay home from work or school to avoid spreading the virus. And, Shuman says, "you can be spreading the virus for a day or two before you start to get symptoms." The key signs include fever, cough, chills, aching muscles and fatigue.

SEE ALSO: Don't Worry About the Antibacterial Soap Ban; Just Wash Properly

Rest and fluids are the best remedy for most people. High-risk populations such as senior citizens should seek immediate medical attention and antiviral treatments — which need to be administered within the first 48 hours of illness to be effective, Shuman says.

Why you should get vaccinated

Although many doctors advise patients to get their flu shots in the fall (or whenever the vaccines are first available), it isn't too late to get the shot now. "I don't think there's really any point where it's too late," Shuman says.

The CDC recommends anyone older than 6 months get a flu shot annually. Because the flu virus mutates each year, protection from a prior shot isn't necessarily effective. A vaccine must be reformulated annually to match the strains expected to be prevalent.