CDC official on why the flu is near-epidemic, peaking early this year

A dangerous flu has been spreading rapidly across the U.S., escalating flu season earlier than usual, and to near-epidemic levels, according to the CDC.

Earlier today, Dr. Daniel B. Jernigan from the CDC, joined "GMA" to address the concerns and misconceptions about this year's flu cycle.

Here are three things to know:

1. The dramatic spike in flu cases

"What we're seeing this year the influenza season started earlier and seems to be peaking right about now," Jernigan, director of the Influenza Division in the National Center for Immunization and Respiratory Diseases (NCIRD) at CDC, told "GMA."

"That's about a month earlier than it normally would be peaking," he said, "so lots of cases [are] happening, in lots of states, all at the same time."

Weather conditions, as well as holiday travel, could have increased the spread of this year's flu, which is showing higher numbers at an earlier time.

"The virus was able to start circulating in time so that, when folks went home for Thanksgiving or they went home for Christmas, they were able to transmit it to the folks that they're with," Jernigan said. "Because of that, it's able to circulate quickly. But we know this particular virus does cause more cases and it can be more severe."

2. This year's flu is different

Jernigan said this year's flu cycle has included more cases of the H3N2 strain of the virus, influenza A, which is usually more severe and difficult to contain.

"Whenever [H3N2] shows up, it causes lots of disease, lots of hospitalizations, lots of cases and lots of deaths," he said.

Over the past couple of years, H3N2 had not been as prevalent.

3. The effectiveness of the flu vaccine

"We know that the influenza vaccine is the best way to prevent, but in this season it is not as effective as it is for the other viruses that circulate," Jernigan said.

Though a recent study raised the idea that the vaccine could be only 10 percent effective against this year's flu, he said that number does not necessarily apply to the U.S. or to other strains of the flu that are circulating, besides H3N2.

"The 10 percent is a very low estimate that came out of Australia over their season last summer," Jernigan said. "The same kind of virus that we had last year was around 30 percent to 33 percent effective for the H3 component. It's actually more effective for the other parts of the vaccine that are trying to prevent the other flus circulating."