The 2022-23 flu season lingered through the second half of January and most of February at the edge of its defined existence, but it now appears to be over.
For the CDC, the annual epidemic known as flu season “occurs when flu activity is higher than a CDC-defined ‘baseline’ value.” That value, expressed as the proportion of all outpatient visits involving influenza-like illness to health care providers in the U.S. Outpatient ILI Surveillance Network, is currently 2.5%.
Over the last 6 weeks, the national figure has been between 2.6% (Feb. 19-25), and 2.7% (Jan. 15-21). In other words, it has lingered like no flu season has lingered before, at least not since the CDC began setting a national baseline in 2007-08.
But for the week of Feb. 26 to March 4, outpatient flu-like illness visits represented just 2.4% of all visits, the CDC’s Influenza Division reported, dropping under the baseline for the first time since the first week of October 2022.
Back then, the early start to the flu season raised concern about a “tripledemic” involving respiratory syncytial virus (RSV) and COVID-19. But by the time the flu season peaked, RSV activity had already started declining and the expected COVID surge never occurred, CDC data shows.
Since the start of the 2022-23 season, the United States has had at least 26 million flu illnesses, 290,000 hospitalizations, and 18,000 deaths, 125 of which were child deaths, the CDC estimates.
CDC: “Weekly U.S. Influenza Surveillance Report,” “National Emergency Department Visits for COVID-19, Influenza, and Respiratory Syncytial Virus,” “National, Regional, and State Level Outpatient Illness and Viral Surveillance.”