The 2018-2019 flu season is in full swing and, according to the Centers for Disease Control and Prevention, the number of cases is rising in 19 U.S. states.

That is more than twice the number of states affected from the week before. As of Dec. 29, the public health agency reported that influenza activity across the country has increased as Influenza A(H1N1)pdm09, influenza A(H3N2), and influenza B viruses continue to spread.

With a few more months left this season, officials are encouraging the public to get their flu shots as soon as possible.

The 2018-2019 Influenza Season Report

In the last week of December alone, 4.1 percent of all doctor visits in the United States was because of symptoms associated with the flu. According to the CDC, this is well above the national baseline, which is 2.2 percent.

The Southern United States, from South Carolina to New Mexico and Utah, is the hardest hit thus far. High levels of flu activity were also reported in New York City and New Jersey.

"It's too soon to say what direction it will go," said Lynette Brammer, head of the CDC, in a phone interview with Bloomberg. "We know right now we are going up, we just don't know when it will start coming back down."

The flu season typically peaks around December to February.

Number Of Children Death Linked To Flu Soars

The CDC also revealed that the highest hospitalization rate is among children under the age of 5. Two pediatric deaths associated with the flu was also reported in the last week of December, bringing the death toll among children to 13.

Children are particularly vulnerable to H1N1, the flu strain that is most dominant this season. Although the H1N1 strain, which is also known as swine flu, tends to cause milder illness, people under the age of 50 are more likely affected. A similar strain circulated about 40 to 50 years ago, giving older age groups residual protection.

There is some good news, however. The death toll this season is nowhere near close to last year's, which reached 185 children dead from the flu. About 80 percent of the children who died last year did not receive a flu shot.