During the Christmas week, flu cases in the United States saw a marked upswing, prompting health authorities to classify this flu season as severe and likely to escalate further. Newly released federal data depict heightened influenza activity surpassing levels observed during the previous winter, which was one of the most severe in recent memory.
Alongside influenza, COVID-19 case numbers have also shown an upward trend according to other federal indicators; however, influenza infections remain more prevalent at this time.
By the week of Christmas, 45 states reported high to very high flu activity, a substantial increase from 30 states the prior week. Public health experts attribute this surge to the predominant flu virus strain circulating this season.
The A H3N2 subtype has been the most commonly detected virus, known historically for causing elevated rates of hospitalization and fatalities, especially amongst elderly populations. Adding to the concern, over 90% of the analyzed H3N2 infections are of a novel subclade, labeled K variant, which deviates from the virus strains targeted by this year’s flu vaccine formulations.
Typically, the peak of flu seasons occurs in January or February. As a result, it remains uncertain how significantly the vaccine mismatch will influence the season's severity.
Last season was notably severe, characterized by the highest flu hospitalization rate since the H1N1 pandemic 15 years ago. Pediatric deaths due to influenza reached 288, marking the deadliest recorded outcome for a standard flu season in the US.
To date, nine child fatalities linked to the flu have been reported this season. The proportion of emergency room visits prompted by flu-related symptoms among children has already exceeded the peak levels seen in the 2024-2025 season. Additionally, influenza-like illness-related visits to doctors’ offices and clinics were higher late last month than any recorded point in the previous flu season.
The Centers for Disease Control and Prevention (CDC) estimates that this season has already resulted in at least 11 million cases of flu illness, 120,000 hospitalizations, and 5,000 deaths nationwide.
In response, the CDC urges all individuals aged 6 months and older who have not yet received their flu vaccine this season to do so promptly to mitigate risks associated with continued virus transmission and severe illness.