With New Jersey still in the deep freeze, thanks to a "polar vortex" bringing in record-breaking cold, it seems a growing number of Garden State residents are getting sick.

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"Officially we're still in the moderate range of flu-like illness activity, but we're definitely seeing levels of influenza-like illness rise throughout our state," said state epidemiologist Dr. Tina Tan. "Particularly in the last week or so, flu is definitely establishing itself here in New Jersey."

Tan said that trend is not really unusual, because this time of year, everyone is spending more time indoors.

"Because you're in closer settings with people who might be sick, you could be potentially more vulnerable to getting ill because of the close contact among people," Tan said.

Even with winter in full swing, Tan stressed that it's not too late to get a flu shot.

"If you haven't gotten your flu shot yet, get the flu shot as soon as possible," Tan said, "because it does take a few days to build immunity."

She said the flu can cause very serious problems for certain groups, including pregnant women, younger children and the elderly. Also, people with weakened immune systems -- particularly those with underlying diseases such as asthma, diabetes and heart disease -- are especially susceptible.

"These folks could have serious complications associated with influenza that could result in hospitalization, and even death," Tan said.