This winter’s flu season has left many people asking the same question: Why does everyone seem to be sick at the same time? Emergency rooms are busier than usual, schools and workplaces are seeing widespread absences, and even people who don’t typically become seriously ill are finding themselves knocked out for days.
It’s not just a feeling. This flu season has already resulted in the highest case counts seen in more than three decades. The Centers for Disease Control and Prevention reports approximately 11 million infections nationwide, leading to an estimated 120,000 hospitalizations and 5,000 deaths. Devastatingly, there were eight pediatric deaths reported in the last week of data (December 28 –- January 3), bringing the total to 15.1
The current, ferocious flu season is being driven by a highly contagious influenza A strain known as Subclade K. It is not a so‑called “superflu” — despite the fact that some people are calling it that — because it does not appear to cause dramatically more severe illness on an individual level.2 Instead, it is Subclade K’s ability to spread quickly — combined with gaps in immunity and changing social behaviors — that has made this one of the most disruptive flu seasons in decades and it is only getting started.
What Makes Subclade K Unusual
Subclade K is a mutated form of influenza A (H3N2), a subtype long associated with more challenging flu seasons. What sets this strain apart is how efficiently it transmits — very easily.
This year’s flu has resulted in a noticeable increase in hospitalizations, including among populations that do not typically require inpatient care. Traditionally, influenza-related hospitalizations are concentrated among older adults, young children, pregnant people, and individuals with chronic underlying conditions such as heart disease, lung disease, diabetes, or compromised immune systems. In a typical flu season, otherwise healthy, working-age adults and adolescents are far less likely to require inpatient care.
This season, however, hospitals are reporting a broader mix of patients. Younger adults, middle-aged individuals, and people without significant preexisting health conditions are being hospitalized at higher rates than expected for complications such as dehydration, high fever, severe respiratory symptoms, and secondary infections. While these patients are not necessarily experiencing more severe disease on an individual level, the sheer volume of infections has increased the number of people who progress to complications requiring medical intervention.
In other words, when a highly contagious strain infects millions more people, even a relatively small percentage developing complications can translate into a substantial rise in hospital admissions — including among groups that are not typically considered high risk for severe flu outcomes, despite the fact that the virus itself is not exceptionally severe.
One source of frustration for both clinicians and patients is that Subclade K was not included in the group of strains targeted by this year’s flu vaccine. As always, flu vaccines must be formulated months in advance, based on predictions about which strains are most likely to circulate. Subclade K emerged and spread after those decisions were made, resulting in a less‑than‑ideal match.3
That mismatch does not mean vaccination is useless for those who are inclined to do so. The flu shot still provides meaningful protection against severe illness, hospitalization, and death by boosting broad immune protection.4 This year, the mismatch is believed to be contributing to the Subclade K’s ability to move rapidly through communities.
Why This Flu Is Spreading So Quickly
The biology of Subclade K is only part of the story. Human behavior and indoor environments play a major role in how respiratory viruses spread.
What Shared Air Reveals About Transmission
A recent large-scale study examining respiratory virus transmission in schools offers important insight into how infections actually spread in real-world indoor settings.5 Rather than relying on self-reported symptoms alone, the researchers combined additional factors like classroom scheduling data and real-time environmental measurements to assess how students were exposed to one another over time.
The findings suggest that spending extended time in the same enclosed space — especially one with limited ventilation — poses a greater transmission risk than momentary closeness or surface contact. Students who shared classrooms for long periods were significantly more likely to become infected than those who only interacted briefly or at close range.
As you read this, you may be wondering: Wasn’t this already established during the height of COVID? In many ways, yes. But what makes this study important is not only the conclusion — it’s how the researchers were able to reach it. Rather than relying on self-reported symptoms or theoretical models, the study reconstructed likely transmission networks and matched them to where, how long, and under what air conditions students were sharing space.
To accomplish this feat, the study was conducted in a large, real-world school setting, with researchers examining respiratory virus transmission using a rare combination of tools: molecular testing, genomic analysis, wearable proximity sensors, classroom scheduling data, and direct measurements of indoor air quality. Or in other words: the research methods allowed for findings beyond modeling and assumptions.
The authors emphasize that these results are consistent with growing evidence that respiratory viruses — including influenza, COVID-19, and RSV — spread efficiently through virus-laden aerosols that accumulate in indoor air. When ventilation and filtration are insufficient, those aerosols can remain suspended and be inhaled by others long after they are released.
With every new research study, indoor air quality continues to reign as a critical factor in virus transmission/prevention. Importantly, these findings are not limited to schools. The same dynamics apply to offices, conference rooms, waiting areas, and other shared indoor environments. This study adds to a growing body of evidence showing that ventilation and air filtration are not secondary considerations, but foundational public health measures — essential not just during pandemics, but during every respiratory virus season.
The Return of “Presenteeism”
Compounding the spread of the flu this season is a behavioral shift back toward a phenomenon known as presenteeism. At first glance, presenteeism might seem like the opposite of absenteeism — and therefore a good thing. In reality, it is anything but positive.
Presenteeism refers to showing up for work despite being ill and symptomatic, often out of a sense of obligation, staffing pressure, financial concerns, or workplace culture. In the United States, presenteeism has historically been treated as a sign of dedication or a strong work ethic. It wasn’t until the COVID-19 pandemic that staying home while ill became a widely accepted social expectation.
As pandemic-era precautions faded, so did that norm. While showing up to work under any circumstances may feel responsible on an individual level, it significantly increases the risk of spreading infection to others.
A study recently published in JAMA Network Open — a peer-reviewed journal of the Journal of the American Medical Association (JAMA) — examined this issue among health care personnel with symptomatic COVID-19. The findings were striking.6 The findings were striking.
In 2020, when awareness of transmission risk was highest, very few clinicians reported working while sick. By 2024, however, more than 15% of symptomatic health care workers reported that they never stopped working during active illness.
Obviously, working while contagious — particularly in health care settings — carries risk. Clinicians care for patients who are often elderly, immunocompromised, or otherwise medically vulnerable. Even when direct patient contact is limited, coming to work while symptomatic increases the likelihood of exposing both patients and colleagues to infection. The study underscores how difficult it is to stay home and isolate while ill, even for medical professionals who absolutely know better.
Surprisingly, the study found higher rates of presenteeism among health care workers with higher incomes (those earning more than $100,000 annually) and higher levels of education. These individuals were also more likely to work in roles with less direct patient contact, which likely reduced their perceived risk of causing harm — but did not eliminate the risk of transmission within shared indoor spaces (especially to colleagues who regularly interact with patients). This demonstrates that workers across the spectrum of pay and education are tempted to partake in presenteeism.
Ultimately, presenteeism is not simply an individual choice. It reflects workplace norms, professional expectations, and systems that still make it difficult — or culturally uncomfortable — to step away from work while ill.
Although the study focused on COVID-19, the implications extend far beyond a single virus. When people attend work, school, or public settings while symptomatic — whether with flu, RSV, or another respiratory infection — they significantly increase the likelihood of transmission. In a season dominated by a highly contagious flu strain like Subclade K, presenteeism amplifies spread and adds avoidable strain to already burdened health care systems.
Why Indoor Air Quality Matters More Than Ever
Clean indoor air is a critical tool for reducing the spread of respiratory illness — and it matters for more than one reason.
First, it has long been understood that breathing cleaner air supports respiratory health and the body’s ability to respond to illness. Poor indoor air quality can irritate airways and place additional stress on the respiratory system, potentially making people more susceptible to infection and slower to recover once they are sick.
Second, as explained in the study outlined above, respiratory viruses spread most efficiently through aerosols that accumulate in indoor air. When ventilation and filtration are inadequate, virus-laden aerosols can accumulate and circulate — increasing the likelihood that others will inhale them over time.
Third, the return of presenteeism adds another layer of risk. As the research shows, people are increasingly coming to work while knowingly symptomatic. This means exposure is not limited to individuals who are about to develop symptoms, but often involves prolonged shared air with people who are already contagious. In that context, indoor air quality becomes an essential line of defense.
For these reasons, experts and public health leaders consistently recommend improving indoor air quality as part of a layered approach to preventing respiratory illness. The Brown University Pandemic Center’s guidance for health leaders repeatedly emphasizes the use of air filtration as a practical, evidence-based strategy to reduce airborne transmission in indoor spaces.7
The Role of High-Performance Air Purification
Not all air purifiers are created equal. Austin Air purifiers are designed with more combined filtration media — including medical-grade HEPA and large volumes of activated carbon — than other air purifiers commonly designed for residential use. This high-capacity approach allows Austin Air systems to continuously capture fine particulate matter, aerosols, and a broad range of gases and odors, supporting cleaner indoor air over extended periods of use.
The Austin Air Immunity Machine, in particular, was engineered with health protection in mind. Its powerful HEPA filtration targets airborne particles associated with respiratory illness, while its extensive activated carbon and zeolite blends address gases and chemical contaminants that can negatively affect indoor air quality and overall respiratory health. Together, this combination helps reduce overall airborne burden in shared indoor spaces — an important consideration during flu season and other periods of heightened respiratory risk.
As the Washington State Department of Health appropriately notes, portable air cleaners are not a standalone solution. They work best when combined with other measures, including source control (keeping sick people home whenever possible) and ventilation with outdoor air when conditions allow. Used as part of a layered strategy, however, high-quality air purification can play a meaningful role in reducing exposure and supporting healthier indoor environments.
Looking Ahead
Subclade K has shown how quickly a highly contagious flu strain can disrupt daily life, even without causing unusually severe disease. The good news is that we already know what works. Staying home when symptomatic and investing in cleaner indoor air can significantly reduce transmission — not just for flu, but for COVID‑19, RSV, and future respiratory threats.
As this season continues, these lessons are worth carrying forward, long after this particular strain fades from circulation.
REFERENCES
1 Weekly US Influenza Surveillance Report: Key Updates for Week 53, ending January 3, 2026. (2026 January 9). Centers for Disease Control FluView. https://www.cdc.gov/fluview/surveillance/2025-week-53.html.
2 Conley M. (2026 January 13). Not a ‘super flu’ but plenty bad: Stanford Medicine expert’s tips for staying safe. Stanford Medicine News Center. https://med.stanford.edu/news/insights/2026/01/not-super-flu-but-plenty-bad-expert-tips.html.
3 Howard B. (2026 January 13). 10 things to know about this year’s surprisingly fierce flu season. Association of American Medical Colleges. https://www.aamc.org/news/10-things-know-about-year-s-surprisingly-fierce-flu-season.
4 Abels G. (2026, January 7). Should you still get the flu shot despite the new strain? Here’s why doctors recommend it. PBS News. https://www.pbs.org/newshour/health/should-you-still-get-the-flu-shot-despite-the-new-strain-heres-why-doctors-recommend-it.
5 Banholzer N, Munday JD, Jent P, et al. (2025 November 27). The relative contribution of close-proximity contacts, shared classroom exposure and indoor air quality to respiratory virus transmission in schools. Nature Communications. doi: 10.1038/s41467-025-66719-3.
6 Crosby JC, Santos Leon E, Chinnock B, et al. (December 2025). Presenteeism Among Health Care Personnel With COVID-19. JAMA Network Open. 2025; 8(12):e2546405. doi:10.1001/jamanetworkopen.2025.46405.
