The strain showed its presence in much of the state the week before Christmas.
High levels of the flu are now showing up in three of the five New Jersey regions monitored by the U.S. Centers for Disease Control and Prevention.
Flu rates are high in the northeast section of the state, as well as in a broad swath across the state's midsection.
During the closing week of 2016, Monmouth County had the most number of positive flu tests, followed by Essex, Bergen, and Ocean counties.
Five counties - Cumberland, Salem, Somerset, Union, and Warren - had not yet had any cases that tested positive for flu. However, health officials say most people who have the flu are never formally tested for the virus.
Illness reports are at a moderate level in the northwest counties, as well as in the southern half of the state, according to figures collected by the N.J. Department of Health
This year's major flu strain is hitting its victims hard, unlike the milder versions that circulated in previous years, said Gary Munk, director of Clinical Virology at Hackensack University Medical Center.
"It's the classic textbook influenza, with high fever, chills, sore throat, headaches, fatigue," he said. "You don't want to get out of bed."
The most prevalent strain among those cases that were tested is the H3N2 strain of the influenza A type.
Munk looked at last year's numbers for comparison and found that while the hospital saw just five cases of flu during the final six weeks of 2015, it saw 72 cases during a comparable period at the close of 2016.
The H3N2 strain is included in the four types targeted by this year's flu vaccine. That means a flu shot is likely to be more effective against prevailing illnesses than during the winter of 2014-15, when the H3N2 variation it included was ot a good match for the type that was circulating that season.
The "swine flu" epidemic of 2009 was a strain that actually produced relatively light symptoms, Munk said, leading some people to conclude the flu isn't really all that bad, and therefore getting vaccinated isn't really necessary.
That attitude is now changing, he said.
"People were reluctant to get vaccinated because they weren't really seeing classic influenza," he said. "Now they're running to get vaccinated, because it's really not something you want to get."
The swine flu strain was also unusual because it had been around three decades earlier than the 2009 outbreak. That meant many Baby Boomers and older people had some residual immunity to it, so weren't hit hard by the pandemic.
This current H3N2, however, is hitting the vulnerable age groups that "bookend" the population - the elderly, and the very young. Infants are vulnerable because many aren't vaccinated, while the elderly are vulnerable simply because of their age.
In addition, even seniors who have been vaccinated could still get the flu if their immune system is sluggish enough to prevent a robust response to the vaccine. "So we want to be careful and watch them" he said.
The recent change in the weather away from unusually warm winter days is only going to accelerate the spread of the flu, Munk predicted.
"It's just going to escalate, because it's getting colder, and we'll be indoors more," he said.
Kathleen O'Brien may be reached at kobrien@njadvancemedia.com. Follow her on Twitter @OBrienLedger. Find NJ.com on Facebook.