(WASHINGTON) — Flu activity is starting to decline nationwide, according to newly released data from the Centers for Disease Control and Prevention.

The CDC estimated on Friday that there have been at least 19 million illnesses, 250,000 hospitalizations and 10,000 deaths from flu so far this season.

Currently, seven states are seeing “very high” levels of flu-like illnesses while 23 states are seeing “high” levels, CDC data shows.

At least 12 flu-associated deaths were reported among children this week, for a total of 44 pediatric deaths this season. Last season saw a record-breaking 289 children die from flu, the highest since the CDC began tracking in 2004.

Despite flu activity on the decline, flu-related emergency department visits for school-aged children between ages 5 and 17 increased since last week while hospitalizations remained stable.

“I think what distinguished this year’s flu season to previous seasons is that, first of all, it began a little bit earlier,” Dr. Daniel Kurtzikes, former chief of infectious diseases at Brigham and Women’s Hospital, told ABC News.

Kuritzkes added that although data does not show that cases increased more dramatically than last year, “we may have perceived it as being worse than it really was, and it now seems like it peaked rather abruptly and is on a rapid decline.”

However, Kuritzkes noted that last year, flu season had a second bump in late winter. He warned that the same thing could happen this year.

Data shows that the majority of this season’s cases are linked to a new flu strain called subclade K — a variant of the H3N2 virus, which is itself a subtype of influenza A.

Subclade K has been circulating since the summer in other countries and was a main driver of a spike in flu cases in Canada, Japan and the U.K.

Dr. Geeta Sood, an assistant professor of medicine at Johns Hopkins Bayview Medical Center, explained that the annual flu vaccine formulation was decided before subclade K emerged, meaning the vaccine is a “mismatch” for the strain, to an extent, while still providing protection against serious disease, hospitalization and death.

“So, this year, we have a couple of problems,” she told ABC News. “One is that the circulating strain that’s predominantly out there is pretty different from the strains that we’ve seen in previous years. … Again, it changes every year, but the amount that it changes can be a lot some years and not so much other years.”

However, she said that early data from the U.K. shows that the vaccine has been protective against serious complications, particularly among children.

“It certainly protects against severe disease, but it’s not one of our best matching vaccines,” Sood said.

Another problem, according to Sood, is that vaccination rates are lower than she would like to see.

As of Jan. 10, 45.6% of adults aged 18 and older and 44.2% of children have received an annual flu vaccine, according to CDC data.

Sood said it’s not too late to get vaccinated, especially because influenza season can last through early spring.

“Even though it takes two weeks to get full immunity, you still get immunity sooner rather than later,” she said. “There’s still plenty of influenza out there, and there’s reactivity to protect you against other strains”

Doctors told ABC News they recommend other hygiene methods, including thoroughly washing hands with soap and water, avoiding crowded places, getting good circulation by opening windows and considering masking.

Richard Zhang, MD, MA, is a child and adolescent psychiatry fellow at Yale School of Medicine and a member of the ABC News Medical Unit.

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