Public health experts are warning of a ''twindemic,'' fearing rapidly rising COVID-19 cases could be joined by a flu outbreak through the holidays, potentially further overwhelming hospitals.

Department of Health and Human Services data shows hospital admissions for flu-like symptoms are up almost 34%, CNBC reported Thursday.

''The most significant problem we are facing is a complete overwhelm of our healthcare capacity,'' University of California, Los Angeles, epidemiology professor Shira Shafir told CNBC.

''When we have COVID transmitting, plus flu, plus all the other things for which someone might need to go to the hospital,'' Shafir added, ''we potentially no longer have the ability to provide care to all of those individuals.''

HHS data is showing flu hospital admissions are rising at a rate much higher than even COVID-19 admissions amid the omicron variant spread, but the seven-day average for the flu is just 250 per day, according to the report.

The last flu season was a light one, never topping a seven-day average of 125 admissions per day, HHS reported. The Centers for Disease Control and Prevention reported a rare year of no flu season in the past cycle, according to the report.

The COVID-19 hospitalization seven-day average is 8,400 the past week, according to the data, up 5% over the previous week. That still pales in comparison with the peak of the delta variant wave over the summer, which data showed seven-day averages of 12,000 daily admissions.

''We do expect that people will have less protection against the flu than they would have in a normal flu situation because we did not have a flu season last year,'' Shafir told CNBC. ''That does leave people particularly vulnerable to influenza this year.''

A CDC survey showed about 48% of U.S. adults have received this season's flu vaccine between Dec. 2 and 13, and  just 9.5% say they plan to get it.

The projection is 57.2% will get the flu vaccine this season, which is 3.4 percentage points higher than last season, according to the report.

''The concerning part is the immunization rates against flu for this time of year are significantly down from where they usually are this time of year, as we move into this holiday gathering period,'' the University of Wisconsin's Dr. Jim Conway told CNBC.

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