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(CNN) —  

At least 1,300 people have died from the flu so far this season, according to a preliminary estimate released Friday by the US Centers for Disease Control and Prevention.

There have been at least 2.6 million flu illnesses and 23,000 flu-related hospitalizations, according to the analysis.

So far this season, the CDC has received reports of 10 children who have died from the flu, four more than the week before.

Experts have warned that flu is hitting the United States early this year, and there are concerns that this early season could mean a particularly severe season overall.

Flu spread significantly in all states except Alaska as of the week ending December 7. Both the eastern and western United States are being hit hard, with widespread flu activity in 23 states: Alabama, Arizona, California, Connecticut, Georgia, Idaho, Indiana, Kentucky, Louisiana, Maryland, Massachusetts, Nebraska, Nevada, New Mexico, New York, North Carolina, Oregon, Pennsylvania, South Carolina, Tennessee, Texas, Virginia and Washington.

For the week ending December 7, health care providers in Alabama, Georgia, Mississippi, Nebraska, South Carolina, Tennessee, Texas, Washington and Puerto Rico saw the highest level of flu activity.

Flu activity is being caused mostly by influenza B/Victoria viruses, which is unusual for this time of year, according to the CDC, and B strains tend to hit children particularly hard. Influenza A/H1N1 viruses are increasing in proportion relative to other flu viruses in some regions, the CDC said.

Flu symptoms, treatment and prevention

People with the flu often experience fever, chills, coughing, sore throat, runny or stuffy nose, muscle or body aches, headaches and fatigue, according to the CDC. Some, more commonly children, may have vomiting and diarrhea. Many people become ill suddenly and recover within a few weeks.

Those who are at higher risk for developing flu-related complications should be treated with antiviral medications as soon as possible. When treatment is started within days of becoming sick, antiviral drugs can lessen symptoms, speed recovery and reduce complications and hospitalizations.

Flu complications, such as pneumonia, can result in hospitalization or even death. Some people are at higher risk for complications from the flu, including children younger than 5 years old, particularly those under 2. Other groups at high risk are adults 65 and older, pregnant women, residents of long-term care facilities and people with weakened immune systems, asthma, heart disease and diabetes.

Hand-washing, avoiding sick people and avoiding touching your eyes, nose and mouth can help prevent the flu. But the most important step to stop seasonal flu is for everyone 6 months or older to get vaccinated, according to the CDC. If the flu is circulating in the area where you live, it is not too late to get vaccinated.

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Although the vaccine won’t prevent all cases of the flu, it lessens the severity and duration of symptoms, and those who get flu after receiving a vaccine are less likely to require hospitalization and less likely to die.