Muscle aches, fevers, chills: the flu can be an unpleasant experience during chilly weather.
The respiratory illness can also be deadly -- 43,000 people in the United States die from it each year, Dr. Neil Fishman, an infectious disease specialist and associate professor of medicine at the Hospital for the University of Pennsylvania, told Fox News.
Understanding what the flu is -- and how to avoid getting it -- may be helpful to your health.
Here's what you need to know.
What is the flu?
The flu “is a very specific disease caused by the influenza virus,” Dr. Lisa Maragakis, the senior director of infection prevention for the Johns Hopkins Health System, said, adding that there can be mild or serious cases.
For one type of the virus, called Influenza A, the “classic” presentation is a sudden onset, Fishman said. People may first have a headache “more in the front of your head or behind your eyes,” with other symptoms being a fever of at least 103 degrees, chills, sweats and body aches.
Influenza B often is less severe and resembles the common cold, but there can be more serious cases, he noted.
What should I know about flu prevention?
The flu vaccine “may not be perfect but it’s the best prevention that we have,” Dr. Daniel Jernigan, the director of the influenza unit at the Centers for Disease Control and Prevention (CDC), said.
Anyone at least 6 months old should get vaccinated yearly, the agency advises.
It’s not recommended for people with “severe, life-threatening” egg allergies or those who have previously had a severe reaction to the flu vaccine, Jernigan said.
As for timing? If you can, get vaccinated by the end of October, the CDC says.
“It takes about two weeks after you get your vaccine to get protected,” Jernigan explained, noting that most flu seasons typically start in November.
"Generally people should start getting vaccinated now," Fishman said, and that they should do so by Halloween to Thanksgiving.
There are other “more general prevention strategies” people can follow, according to Maragakis. These include frequently washing your hands, coughing and sneezing into the crook of your elbow and avoiding people who appear to be sick.
I have the flu -- now what?
“If it’s a mild illness, it’s generally self-limited,” Maragakis said. If you’re sick, stay home and avoid others, especially babies, pregnant women and the elderly, she advised.
Jernigan encouraged people with the flu to get lots of fluids and nutrients. Antiviral drugs are used when people are hospitalized or have certain underlying medical conditions, he said.
These types of drugs can also be used in less serious cases, according to Fishman. Other flu remedies include getting lots of rest, following a healthy diet and taking Tylenol or Advil, he said.
“None of the homeopathic drugs have really been shown to help influenza,” he said, noting that you should check with a doctor or a pharmacist to see if “natural” products interfere with other medications.
How effective is the vaccine?
“While vaccine effectiveness may vary, recent studies show that flu vaccination reduces the risk of flu illness by between 40 percent and 60 percent among the overall population during seasons when most circulating flu viruses are well-matched to the flu vaccine,” the CDC says online.
The agency collects viruses in the world “and determines how close they are to a virus that goes into the vaccine,” Jernigan explained.