Government health officials and the leader of Sentara Healthcare’s flu taskforce are reporting increased flu activity this year among the young and middle-aged.

As of the week ending Jan. 18, the federal Centers for Disease Control and Prevention reports the largest proportion of flu hospitalizations this season were in the 18 to 49 age group, at 31.7 percent.

People aged 50 to 64 accounted for 29.5 percent, while the rate for people aged 65 and older — a group usually accounting for the most hospitalizations and deaths — stood at just 23 percent.

The CDC thinks this is because older people had existing antibodies against H1N1, which is this year’s predominant strain, coming into the season, “perhaps because they were exposed to similar viruses — predecessors of 2009 H1N1 viruses — earlier in their lifetimes.”

Scott Miller, an infectious disease specialist who leads the Sentara taskforce, said the flu is hitting the 25 to 49 age group significantly more than in previous years.

He said he thinks this might also be because younger people believe they are less susceptible and therefore don’t get vaccinated.

“We’ve got the dual-whammy effect of folks who are probably not old enough to have any natural antibodies … and they are the ones that need to frequent the doctor’s office and get a vaccination,” Miller said.

Along with most other hospitals, Suffolk’s Sentara Obici is seeing flu cases, he said, “but they are keeping up in the emergency department and their critical-care (unit).” The biggest risk is in the birthing unit, he added, as newborns have little immunity.

“When people come into a health care facility, they should really avail themselves of the masks and the hand sanitizer, because we really don’t want to be an area where we spread this virus,” Miller said.

The Virginia Department of Health’s latest weekly flu activity report, for the week ending Jan. 17, shows flu has been widespread — the highest level — since the second-to-last week of 2013. Widespread activity started one week earlier in 2012-2013 and persisted through week 10 of the New Year. The report is based on emergency department and urgent care data.

Bon Secours’ Carl Wentzel, medical director for the health care provider’s emergency departments at North Suffolk’s Harbour View and Maryview in Portsmouth, said this area’s first flu cases arrived about Jan. 1.

“Since that time, it’s picked up,” he said. “We are seeing more of it,” though the season is not yet as severe as in past years.

“I hope that’s because people have taken the advice and gotten flu shots. I guess we are three to four weeks into it, and we are waiting to see if it’s really going to take off. We have still got a couple of more months to go.”

Wentzel said people are getting better and better each year at following the recommendation to wear masks in health care facilities during flu season.

“The first time we did it, a few years ago, there was some reluctance or lack of understanding,” he said. “This year I don’t see any problem with it. You walk around the hospitals, and you see visitors wearing masks.”

He attributed the lack of flu outbreaks at Harbour View or other Bon Secours facilities to the widespread compliance with the mask recommendation.

Meanwhile, Miller said it’s still not too late for those who haven’t been vaccinated this season to get their shots.

To avoid getting the flu or spreading it, wash your hands often, cough into a tissue or the inside of your elbow instead of your bare hand and get a flu shot if you haven’t already, health officials suggest.