(CNN) -- An early and severe start to the flu season has many health experts concerned. On Friday, the Centers for Disease Control and Prevention reported 47 states are experiencing widespread activity, although it appears to be decreasing in some areas.

According to the CDC, this is the most flu cases they've seen at this time of year in more than a decade. Twenty pediatric flu-related deaths have occurred since the start of the season. The CDC does not track adult flu-related deaths.

The peak of the season, which usually happens in February, may be yet to come for most states -- officials said Friday it may be a week or two before it becomes clear whether cases have peaked.

The type of flu that is going around is called Influenza A (H3N2), which is often linked to more serious diseases than other flu varieties, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, told CNN. People could get more complications from this particular strain, which would make them sick for a longer period of time.

The 2011-2012 flu season began late and was relatively mild compared with previous seasons, according to the CDC. In fact, the season's peak set a record for the lowest and shortest since surveillance began.

The number of pediatric flu-related deaths was also low last year. The CDC reported 26 children under the age of 18 had died by May 25, 2012. As a comparison, 122 pediatric flu-related deaths were reported during the 2010-2011 season.

The flu kills about 36,000 people a year in the United States, according to the CDC, though the range varies greatly each year. Most deaths are caused by complications from the flu.

Children under 2 years old, adults over 65, pregnant women and American Indians are at a greater risk of suffering from flu complications, according to the CDC. People with medical conditions like asthma, lung disease, heart disease and people with weakened immune systems are also at risk.

Most of the people who die have underlying illnesses or a weakened immune system, says Dr. Sanjay Gupta, CNN's chief medical correspondent. The flu can weaken the immune system even more, which can lead to a complication like a bacterial infection.

"It is that bacterial infection that most often causes death, especially in the younger population," Gupta says.

Most people with the flu don't have to -- they'll recover on their own in five to seven days with plenty of rest and fluids, says Dr. David Zich, internal medicine and emergency medicine physician at Northwestern Memorial Hospital in Chicago.





Could Be Worst Flu Season In Years