Flu epidemic hits US, hospitalizations climb during peak season

The Centers for Disease Control and Prevention (CDC) believes the nation is at peak flu season, as the disease is now considered to be an epidemic, based on its medical impact, the federal agency said today.

The rate of hospitalizations for pneumonia and the flu is continuing to climb amid a CDC warning of several more weeks of significant flu activity.

"It's a busy flu season this year," Dr. Jesse Jacob, associate professor of medicine at Emory University School of Medicine, told ABC News today.

"We're seeing a lot of patients with the flu compared to last year," Jacob said. "We've tested nearly twice as many patients as we have the year before and we're seeing about four times as much flu."

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

"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."

There were seven pediatric flu deaths last week, bringing the total to 20 for the flu season that started Oct. 1, the CDC said.

Trips to the doctor for flu-like illnesses might be starting to stabilize; 26 states were reporting high-levels of outpatient visits, the same as the prior week.

High flu activity has been reported in New York City as well as Alabama, Arizona, Arkansas, California, Colorado, Georgia, Illinois, Indiana, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Nebraska, Nevada, New Jersey, New Mexico, Ohio, Oklahoma, Oregon, South Carolina, Texas, Virginia, Washington, West Virginia and Wyoming, the CDC said.

Outbreaks of the flu have closed some schools in states including Alabama, Idaho, North Carolina, Tennessee and Texas.

Antiviral drugs are also approved and recommended for treatment if taken within 48 hours of the beginning of symptoms. They can prevent serious complications from the flu, the CDC said, particularly for people in the highest risk groups: children younger than 5 and adults older than 65.

Influenza H3N2 has been the most common strain in this cycle, which is usually more severe, the CDC said.

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

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

"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 Australian study raised the idea that the vaccine might be only 10 percent effective against this year's flu, he said that estimate does not necessarily apply to the United States, or to other strains of the flu that are circulating.

"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."

The flu vaccine is still recommended, the CDC said, explaining it's not too late to get the shot because many weeks of flu season remain.

"It's never too late" to get the vaccine, Jacob said, "because the flu season can go on for months. It takes the vaccine about a week to really kick in. But if you're at risk, which pretty much anyone out there is right now, you haven't gotten the flu shot, you should get vaccinated. ... That's the recommendations from the CDC.

"I think one of the other major things is to stay out of work or school if it's possible if you're sick, to try to keep everyone else around you healthy," Jacob said. "And wash your hands."

ABC News' Steve Osunsami, Allie Busalacchi and Kelly McCarthy contributed to this report.