An uptick in flu cases involving H3N2, a variant associated with severe illness in previous years, may portend a busy flu season, a Yale New Haven Health official said Wednesday.

On top of COVID-19, “it’s a little worrisome” and could prove challenging for health care providers, Dr. Thomas Balcezak, the health system’s chief clinical officer, said during a virtual news briefing.

“It will certainly be worse than last year since there was none last year,” he said of the flu. “There’s not a lot of immunity, so it can easily spread. The message is to get a flu shot this year, even if you don’t usually.”

Balcezak and Marna Borgstrom, Yale New Haven Health’s chief executive officer, reported the system’s hospitals, including Lawrence + Memorial Hospital in New London and Westerly Hospital, are exceptionally busy due to people seeking care deferred during the height of the coronavirus pandemic. Cases of COVID-19 continue to climb, too, though they are nowhere near peak level, Borgstrom said.

She reported the system’s five hospitals were treating 210 COVID-19 patients, down from 437 a year ago but up since September, October and November. Fifty-one of the current patients are being treated in intensive care units, 24 of them on ventilators.

On Wednesday, L+M had 20 of the 210 patients and Westerly had 13.

Statewide numbers released by Gov. Ned Lamont’s office show 1,723 new coronavirus cases had been detected among results of 24,082 new tests, a one-day positivity rate of 7.15%. Thirty-five additional hospitalizations had pushed the total to 716.

During a meeting of the Southeastern Connecticut Council of Governments, Stephen Mansfield, director of health for the Ledge Light Health District, said the rate of cases in both Ledge Light and Uncas health districts is the highest it’s been since January.

In January, he pointed out, schools were in hybrid mode or fully remote, sports were limited and restrictions on businesses still were in effect.

Balcezak said more than 75% of the COVID-19 patients Yale New Haven Health hospitals are treating have not been vaccinated against the disease. That percentage holds up statewide, according to the governor’s office.

On average, about 75% of the population has had at least one dose of a COVID-19 vaccine in the area that comprises East Lyme, Groton, Ledyard, Lyme, Montville, New London, Norwich, North Stonington, Old Lyme, Preston, Salem, Stonington and Waterford as of Dec. 8, according to state data. Lyme had the highest vaccination rate, at 92.06%, while North Stonington and Groton had the lowest rates, at 64.8% and 65.85%, respectively.

Asked about the coronavirus omicron variant, Balcezak said it still is too soon to say how effective existing vaccines will be in fighting it. So far, the available data suggests omicron may spread more readily, but is slightly less dangerous, than other variants.

“If its severity is less, that’s good,” he said.

Given the increase in cases, a trend expected to continue beyond the upcoming holidays, omicron likely will become the dominant variant in the U.S. early next year, Balcezak said.

Yale New Haven Health is treating COVID-19 patients with monoclonal antibodies and other medications, and hopes to provide, on an outpatient basis, two antiviral drugs the U.S. Food and Drug Administration is expected to approve in coming weeks. In the meantime, the system is keeping testing sites open to meet demand among those preparing to travel or gather in groups.

Mansfield said some New London County testing sites have been somewhat overwhelmed by demand, in part because so many unvaccinated people are required to get tested on a regular basis. He said 100 cars lined up in the first hour at a clinic Tuesday night in the City of Groton.

Yale New Haven Health, which, like all hospitals in the state, mandated its employees be vaccinated, is considering requiring they receive booster shots as well, according to Balcezak.

Day Staff Writer Kimberly Drelich contributed to this report.

b.hallenbeck@theday.com