Flu activity could continue to increase in the U.S. over the next few weeks, according to a top flu epidemiologist at the Centers for Disease Control and Prevention.

"There's a lot of influenza out there right now," Dr. Carrie Reed, chief of the epidemiology and prevention branch of the CDC's influenza division, told ABC News.

"We often see activity continue into the spring ... I think the reality is that it's going to continue to be elevated for a little bit longer," she continued.

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The CDC's latest estimates indicate that there have been at least 11 million illnesses, 120,000 hospitalizations and 5,000 deaths from flu so far this season.

"That's likely a low estimate based on the data that we're seeing so far," Reed said, adding that the federal health agency typically publishes the lower range of the estimates.

A new variant that first emerged in the summer, known as subclade K, has become the dominant strain, CDC data shows. Subclade K is a variant of the H3N2 virus, which is itself a subtype of influenza A.

Of the 994 flu samples tested since Sept. 30, nearly all were influenza A. Of those samples that underwent further testing roughly ​90% were H3N2, CDC data shows.

"Subclade K has acquired some mutations in the virus that make it a little bit different than what's in the vaccine and what was circulating over the last couple years," Reed said.

Public health experts currently recommend that everyone ages 6 months and older, with rare exceptions, get an annual flu vaccine.

Although the current flu vaccine is not a perfect match to subclade K, it is still expected to offer some protection against the new variant and lower the risk of serious disease, hospitalization and death.

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Reed added that the new variant does not appear to be driving more severe illness yet.

"There are still benefits to vaccine, even if the virus [has] somewhat drifted from what's in the vaccine," she said. "We haven't seen increases in hospitalization and mortality yet in the ways that we have with [doctors' visits], although that's something that we continue to watch for as well."

For those who have gotten sick, there are medicines available, known as antivirals, that may help reduce the severity and length of illness.

Reed said for those who contract the flu and have a higher risk of severe disease, they should seek care early and speak with their doctor about receiving a prescription for flu antivirals.

She explained that flu antivirals have been found to reduce the duration of illness as well as lower the risk for severe disease, hospitalization and death.

Health officials have stressed that it is not too late for people get a flu shot if they haven't received one yet.

"There's still time to get a flu vaccine," Reed said. "It does take a couple weeks for your immune response to pick up after vaccination, but that does mean there's many more weeks of flu activity to benefit from the protection of an influenza vaccine."