Flu season is here. Here’s what you can do about it.

Holidays are upon us — and so is the flu.

More Americans are getting infected with seasonal influenza and seeking care, according to Centers for Disease Control and Prevention data.

“It is clearly the season,” Dr. Eduardo Azziz-Baumgartner, a medical epidemiologist in the Centers for Disease Control and Prevention’s Influenza Division, told USA TODAY.

One important step, if people haven’t done so, is to get vaccinated, he said. Full protection takes a couple weeks to kick in, but it has benefits in preventing serious illness.

“The flu season still has weeks to go, so they will still get protection from the flu shot if they get it soon,” he said.

Last year, the flu led to 470,000 hospitalizations and 28,000 deaths.

Along with COVID-19 and other respiratory viruses, the flu thrives in colder winter months as people spend more time indoors.

Here is what to know about where the flu is currently spreading and how to protect yourself.

Where is flu circulating?

Seasonal flu viruses are dominated by influenza A and B.

Most seasonal flu viruses are influenza type A, which usually start earlier in the season, with type B viruses circulating later in the winter. Currently, A viruses, of H1N1 and H3N2, are circulating with activity in many southern and western states, CDC data shows.

Wastewater surveillance, a tool used to detect diseases from municipal treatment plants, similarly shows high levels of influenza A circulating across the U.S., in addition to SARS-CoV-2, which causes COVID-19, and respiratory syncytial virus. Influenza B transmission is low for now.

Annual flu vaccines are based on recommendations from a federal advisory committee that looks at viruses causing disease last year, how viruses have changed, and disease trends, according to the Food and Drug Administration.

Vaccines appear to be largely effective against currently circulating viruses, despite earlier concerns that they might not be, according to Richard Webby, a virologist at St. Jude’s Children’s Research Hospital, in Memphis, Tennessee.

Vaccination remains much lower than in prior years, said Azziz-Baumgartner, of CDC. Last year, only about half of Americans received their annual flu shot.

Who is at risk for severe infection

With the flu, someone can have a relatively mild sickness that lasts only a few days, or end up with severe illness that lands them in the hospital. Former President Bill Clinton, age 78, just spent Monday night in the hospital to get treated for the flu, for example.

The flu virus spreads mainly by droplets released when people cough, sneeze or talk. But, unlike the virus that causes COVID-19, people can also spread it by touching surfaces where droplets have landed, and then touch their nose, mouth or eyes.

Some people are at greater risk for serious complications from the flu, such as older adults, people who are pregnant, young children and anyone with chronic health conditions like asthma, diabetes or heart disease.

Is it the flu, cold or something else?

Flu symptoms vary, but they typically include:

• fever or feeling feverish or chills,

• cough,

• sore throat,

• runny or stuffy nose,

• muscle or body aches, or fatigue or tiredness,

• headaches,

• vomiting or diarrhea, though this is more common in children.

With respiratory viruses, including the common cold, it can be hard to tell what’s behind a cough and sneeze, and maybe fever. But there are some signs.

Symptoms for COVID-19 can show up later than a cold or the flu, according to the Mayo Clinic. A fever is rare and muscle aches and tiredness don’t happen with a cold.

A headache is also common with flu and COVID-19, but it’s not typical with a cold. A dry cough is more common with COVID-19 than flu.

What can I do to protect myself?

A flu vaccine for everyone ages 6 months and older is crucial, Azziz-Baumgartner, of CDC, said. In addition, people should prevent the spread of germs.

This includes frequent hand washing with soap and water, covering coughs and sneezes, and avoid touching your eyes, nose and mouth, CDC said.

Like other respiratory viruses, people should avoid contact with others who are sick. If you're sick, you should stay home until both your symptoms are improving and you haven't had a fever for 24 hours.

Antiviral drugs prescribed by a doctor can treat the flu, but not colds and different ones are needed for COVID-19. They're best when used within a few days of developing symptoms.

A face mask can also reduce risk of you or someone else spreading the flu.

How long am I contagious?

Most healthy people with the flu can infect others for about a day before symptoms show, and up to a week after no longer having symptoms, according to Dr. Pranita Tamma, a pediatric infectious disease specialist at Johns Hopkins Children’s Center, in an article.

People with weakened immune systems can be contagious for several weeks.

(This story was updated to correct an error.)

This article originally appeared on USA TODAY: Cough, sneeze, fever: Flu season arrives for holidays