The United States is preparing for what could be another record-breaking influenza season, with health officials raising the alarm over a new flu variant spreading globally that shows an ability to partially evade immune defences.
Experts predict the 2025-2026 respiratory virus season could match or even surpass the devastating figures from the previous year, which saw an estimated 47 to 82 million illnesses and a tragic 27,000 to 130,000 deaths. This made it the most severe flu outbreak in nearly a decade and one of the most intense in at least 15 years, characterised by exceptionally high rates of hospitalisations and paediatric deaths.
The New Threat: Subclade K
The primary cause for concern is a new variant of the existing H3N2 influenza A virus, which has been dubbed 'Subclade K'. This strain is causing international worry due to its capacity to bypass some of the body's immune system responses and the protection offered by the seasonal vaccine.
Subclade K is thought to have emerged towards the end of the Southern Hemisphere's flu season and has since spread rapidly in several countries, including Japan, the UK, and Canada. It is expected to reach the United States in the coming weeks. Early data from the UK and Japan suggests it already constitutes a significant portion of most flu samples analysed there.
Critically, the current recommended flu vaccine in the US is not designed to protect against Subclade K. The seasonal jab is formulated to block the influenza A viruses H1N1 and H3N2, along with the influenza B Victoria virus, but does not specifically target this new subclade.
Plummeting Vaccination Rates Compound the Crisis
This new viral threat arrives as flu vaccination coverage in the US continues to slip steadily since the COVID-19 pandemic. Recent data from the Centers for Disease Control and Prevention (CDC) reveals a worrying decline.
In the 2023–24 season, only 55.4 percent of children (ages six months to 17 years) received a flu shot. This represents a two-percentage-point drop from the prior year and is a stark 8.3 points below pre-pandemic levels seen in 2019–20. For adults, the situation is even worse, with just 44.9 percent vaccinated, also two points lower than the previous year.
This decline in childhood immunisations has been partly driven by online misinformation and the political divisions that emerged around COVID-19 vaccines, a sentiment that Health Secretary Robert F. Kennedy Jr. has been noted to echo.
Early Signs of Growing Flu Activity
Current tracking indicates that flu cases are likely growing or currently increasing in all reporting states. As of the latest data, influenza makes up two percent of positive lab tests for all respiratory specimens.
Visits to doctors for influenza-like illness have also seen a slight uptick, now accounting for 2.1 percent of all medical visits. This early indicator suggests a rise in flu activity, with much of the increase reportedly being driven by children and younger adults.
Following a temporary hiatus due to a record-breaking government shutdown, the CDC resumed its flu surveillance reports in November 2025. For the week of November 3 to 9, the agency reported 1,665 influenza-associated hospitalisations, marking a five percent increase from the week before. The current hospitalisation rate stands at one per 100,000 people, a figure that pales in comparison to the peak of last year's season, which reached 13.5 per 100,000.
Nationwide, levels for flu and respiratory syncytial virus (RSV) are currently classified as low but are increasing. States like Alabama and New Hampshire are already experiencing moderate levels of respiratory illness.
Symptoms and Serious Risks
Symptoms for the Subclade K strain are similar to other flu viruses, commonly including high fever, severe body aches, and fatigue. However, anecdotal reports from Australia, where the variant has already circulated, suggest it may cause more intense body aches, longer-lasting tiredness, and a more sudden onset of symptoms.
The inflammation caused by the flu can impair the lungs' ability to transfer oxygen, raising the risk of deadly complications such as pneumonia, respiratory failure, sepsis, and inflammation of the heart or brain. The virus can also severely worsen pre-existing chronic conditions like asthma and heart disease, often necessitating hospitalisation.
Older adults in nursing homes are at a particularly heightened risk. During the 2021-2022 season, the death rate for people aged 65 and older was approximately 7.4 per 100,000, compared to just 0.1 per 100,000 for those aged 18 to 49.
Despite the new variant's ability to partially evade immunity, the CDC and other health bodies strongly emphasise that immunisation remains the best defence against serious illness from all flu strains. They advise that everyone aged six months and older should receive an annual flu vaccine.
