As winter tightens its grip, the United States is grappling with a concerning dual surge in respiratory illnesses, driven by a potent new influenza strain and the latest dominant Covid variant. Fresh data from the US Centers for Disease Control and Prevention (CDC) paints a stark picture of rising infections and hospitalisations across the country.
A Perfect Storm of Winter Viruses
The latest CDC figures, current up to 6 December, reveal a sharp 13% week-on-week increase in positive influenza tests. More alarmingly, hospital admissions for flu have leapt by nearly 50% compared to the previous week. When measured against the same period last year, the situation is even more severe: positive tests are up by almost 50%, and hospitalisations have more than doubled.
Experts attribute this dramatic spike largely to the rapid spread of a dangerous new flu strain known as H3N2 subclade K. This variant is now circulating in over three dozen states and is considered brand new to most people's immune systems, leaving populations highly vulnerable to severe, hospitalising illness. The CDC reports that 89% of influenza A samples tested since September belong to this H3N2 subclade K.
Transmission levels are already classified as 'very high' in several regions including New York City, New Jersey, Colorado, and Louisiana. The impact is being felt on the ground: several schools nationwide have temporarily closed after hundreds of students fell ill with flu-like symptoms, and a growing number of hospitals have reinstated mask mandates for staff, patients, and visitors.
Symptoms and Spread of the 'Super Flu'
So far this season, approximately 3 million Americans have contracted influenza A, which accounts for three out of every four flu cases. The CDC has reported around 30,000 hospitalisations and 1,200 deaths. Tragically, the agency has also confirmed the first paediatric flu death of the 2025-2026 season, with Colorado health officials verifying a child's death this week.
Symptoms of the so-called 'super flu' are consistent with typical influenza A but may be more severe. They include:
- Fever and chills
- Cough and sore throat
- Runny or stuffy nose
- Muscle aches, headaches, and fatigue
- Vomiting and diarrhoea (more common in children)
Individuals are contagious from about a day before symptoms appear until five to seven days after falling ill. While most recover within a week, a cough and fatigue can persist for over two weeks. Health officials emphasise that the annual flu vaccine remains the best preventative measure, alongside rigorous hand hygiene and avoiding contact with symptomatic individuals.
Covid's New Dominant Variant: XFG (Stratus)
Simultaneously, the Covid landscape is being shaped by a new dominant variant. CDC data shows that strain XFG, also referred to as Stratus, now accounts for the majority of cases. While many symptoms mirror those of flu, patients infected with this variant have reported a distinct and painful 'razor blade sensation in the throat'.
A key symptom that differentiates Covid from influenza is the potential loss of taste or smell. According to wastewater surveillance data, which tracks community spread, national Covid viral activity was rated 'low' as of 6 December, with the Northeast showing the highest levels. However, the trend is worrying: the spread is worsening in nine states and declining in only four. Indiana is the sole state currently reporting 'very high' Covid wastewater activity.
Test positivity for Covid has risen to 3.6%, up from 3.1% the prior week, though hospitalisation rates have held steady. The CDC's trends data indicates that the spread of both influenza and Covid is likely to intensify in the coming weeks, signalling a challenging winter period for public health.
