Public health authorities are seeing signs of a second wave of increased flu activity, particularly in the Midwest and parts of the South, after a post-holiday lull of respiratory illness.

Why it matters: More than half of Americans haven't had a flu shot, per the Centers for Disease Control, increasing the odds for sustained high levels of disease spread through February and posing challenges for some stressed medical systems.

• While outpatient visits for flu-like symptoms have been consistently above the national baseline since November, CDC data for the week ending Jan. 27 found an increase for one age group, those between 5 and 24.

By the numbers: 16.2% of clinical lab samples tested positive for influenza for the week ending Jan. 27, compared with 14.4% the previous week.

• There were eight pediatric deaths associated with influenza during the week, bringing the 2023-2024 season total to 65 pediatric deaths.
• CDC estimates that there have been at least 20 million illnesses, 230,000 hospitalizations and 14,000 deaths from flu so far this season.

Surveillance data showed Georgia, New Mexico, New York City and South Carolina had "very high" flu activity, followed by nine other states mostly in the South, plus the District of Columbia.

• A second flu wave is commonly seen during wintertime and is sometimes associated with the aftereffects of holiday travel and people putting off needed care.

Yes, but: While flu is rebounding, most COVID-19 metrics are declining, except for deaths, which held steady, per the University of Minnesota Center for Infectious Disease Research and Policy, or CIDRAP.

• Hospitalizations for COVID, one of the most closely watched indicators, fell 10.9% last week compared with the previous week.
• RSV activity has also declined across many parts of the nation, and hospitalizations are falling among young children, CIDRAP noted, citing CDC data.

The bottom line: Flu remains the key driver of this year's tripledemic, though the amount of respiratory illness — defined as fever plus cough or sore throat — causing people to seek out care is elevated but declining in some areas of the country, the CDC said.