Seasonal illnesses are spreading across the United States just as the holiday travel rush begins, raising concerns among health officials about new outbreaks during family gatherings.
Influenza and norovirus cases are climbing in several states, while COVID-19 continues to circulate at lower but steady levels. Together, these infections are increasing pressure on hospitals as millions prepare to travel in the coming days.
What is super flu?
The current flu surge is due to a mutated strain of influenza A, called H3N2 subclade K. Health authorities say this strain has now become the dominant flu variant in the US, making up about 89 percent of H3N2 cases analysed since late September, based on genetic sequencing data from the Centers for Disease Control and Prevention (CDC).
This variant appeared after the 2025–26 flu vaccine was developed, which means the vaccine may not be as closely matched as in previous years. The shot still helps protect against severe illness, experts say the mismatch could allow the virus to spread more easily.
What symptoms should people watch for?
The symptoms linked to the current flu wave remain familiar. People may experience fever, chills, severe fatigue, cough, and body aches. However, doctors warn that the increased spread could lead to a higher number of serious cases, especially among vulnerable groups.
CDC estimates show that the US has already recorded around 4.6 million flu cases, with 49,000 hospitalizations and 1,900 deaths so far this season. Flu activity rose sharply in mid-December, with test positivity climbing from 8.1 percent to 14.3 percent in just one week.
Norovirus outbreaks add to concerns
Norovirus, often referred to as the “winter vomiting disease”, is also spreading widely. Wastewater data shows viral levels have risen by 69 percent nationwide since October, according to WastewaterSCAN, which currently rates the national risk as “high”.
The largest increases have been seen in the Northeast and Midwest, with additional outbreaks reported in Illinois and Texas. Hospitals in affected areas have reported more emergency visits linked to stomach-related illness. The CDC noted that norovirus test positivity reached nearly 14 percent by mid-November, twice the level seen earlier in the fall.
Schools report rising absences
Children have been among the hardest hit. In Marin County, California, nearly one in three students at a school were absent with flu-like symptoms. Schools in parts of suburban Chicago temporarily shifted to online learning due to similar outbreaks. In New York City, school attendance dropped as pediatric flu cases increased. Several districts increased cleaning and disinfection efforts ahead of the winter break to limit further spread.
Holiday travel could worsen spread
The spike in infections comes as holiday travel is expected to break records. AAA estimates that 122 million people will travel across the U.S. between December 20 and January 1. Health officials warn that packed airports, public transport, and large family gatherings create ideal conditions for viruses to spread rapidly.
How to reduce the risk
Doctors advise people to stay home if they feel unwell, wash hands frequently, especially to prevent norovirus, and consider getting vaccinated against flu and COVID-19. Even with a weaker strain match, experts say vaccines continue to play a key role in preventing severe illness, hospitalization, and death.