Omicron and delta may be hogging the headlines, but flu is spreading, too, raising the possibility that the “twindemic” of flu and COVID-19 that public health leaders wrongly predicted last year might actually happen this year.

In its latest weekly report on flu, the Pennsylvania Department of Health characterized flu activity during the week ending Dec. 11 as high and increasing. A total of 8,583 laboratory-confirmed influenza cases have been reported so far in all but two of the state’s 67 counties. That includes 2,466 cases in Philadelphia and the four suburban counties. It is surely an underestimate, the state said, because most people with flu do not see a doctor or seek testing.

However, public health leaders say testing for flu is likely unusually high this year, because that is the only sure way to differentiate between flu and COVID-19.

The state estimates that 120 to 2,000 people die of flu complications each year in Pennsylvania. So far this season, there have been three known deaths.

The state data show that cases are rising unusually fast for this early in the season — faster than in any of the last eight years. Last year, there were very few flu cases as people isolated due to COVID and wore masks during rare trips into public spaces.

In its report for the week ending Dec. 11, New Jersey said spread in the state is moderate. So far, the flu season seems to be following a typical pattern. However, flu activity is high in northeast and central east counties. Positive flu tests are rising.

Several other respiratory viruses, including rhinovirus and respiratory syncytial virus, are also circulating.

The CDC said flu activity was low but increasing nationwide during its most recent report for the week ending Dec. 4. New Mexico is a hot spot.