Winter Viral Illness Season: Breathe Easier with Athlytic
As we enter the 2025–26 respiratory virus season, many clinicians are bracing for a particularly challenging winter. We all know that upper respiratory infections become more commonplace in winter, bringing on the coughs and sniffles. There are a number of likely factors that contribute to the rise of viral illnesses in the winter months (1). For one, spread becomes more likely with the movement of children in and out of schools, holiday gatherings, and the cold weather leading people to spend more time indoors and in closer contact. In addition, viruses may be able to live longer/spread more effectively with the temperature, UV, and humidity changes associated with the winter season. Lastly, there is a likely dip in our own immune system function, associated with changes to circadian rhythm, light/dark cycles, and even vitamin D levels.
With this in mind, it’s also important to note that the 2025-2026 season has shown signs of starting earlier than previous years, shaping up to be a more severe year overall (2). One of the dominant flu strains this year has shown several mutations leading to this change.
What can we do to protect ourselves?
Like most goals in medicine, prevention is key. The high mutagenicity (the ability of the virus to change itself) of influenza can make it tricky for our immune system defend itself. Yearly vaccines attempt to keep up with the changes to give your immune system a head start. Even if the dominant strain ends up being different from the strains included in the vaccines, it still offers protection by reducing the severity and duration of subsequent illness. Indeed, just getting the vaccine has been shown to decrease the risk of having a heart attack or dying of cardiovascular disease overall (as severe infections can be quite taxing on our bodies!) (3).
Beyond this, regular healthy habits can also significantly reduce spread. Wash your hands often, and avoid touching your eyes, nose, and mouth. If you have symptoms of an illness, avoid close contact, cover your mouth/nose with coughing and sneezing, and stay home if possible.
Luckily for us, Athlytic offers several ways to track our health metrics, which may provide early insight into oncoming illness and its severity. While no wearable can diagnose a virus on its own, devices that monitor resting heart rate (RHR), heart rate variability (HRV), and respiratory rate (RR) are increasingly shown to pick up signs of infection before symptoms become obvious, offering a head start.
In fact, researchers analyzed smartwatch data from individuals who eventually tested positive for COVID-19 and found that in 81% of cases, significant shifts in resting heart rate and activity occurred before—or right at—symptom onset, with some anomalies detected days earlier (4). Why do these wearable metrics change with infection? The answer lies in your autonomic nervous system (see Episode 4 for more). As your innate immune system ramps up in response to a viral threat, there is a shift in autonomic balance: sympathetic activation increases, and parasympathetic activity decreases. This physiological rebalancing results in a measurable increase in heart rate and a drop in HRV, because your body is reallocating resources toward defense rather than rest. Decreases in HRV have also been shown to predict an inflammatory response in the body even before blood markers of inflammation started to rise (5)!
This is exactly where Athlytic can bring tangible benefits during high-risk seasons. By building your personal baseline over weeks of healthy data, the app learns your normal ranges for RHR, HRV, sleep, and respiratory rate. When your data begins to drift (ie. your overnight RHR is elevated, HRV is suppressed, or your breathing is subtly faster than usual) these can be flagged as potential early signs of viral stress. This offers an individually tailored approach: what’s unusual for you might be totally normal for someone else.
Now, not every HRV dip is infection (training stress, alcohol, jet lag, dehydration, or poor sleep can cause similar signals). However, when Athlytic detects such multi-parameter changes consistently over 1–3 days, it can prompt you to take precautionary actions.
Of course, wearable data is not a substitute for medical testing or professional care. These signals are early warnings, not definitive diagnoses. Their strength lies in being non-invasive, continuous, and individualized. But when used wisely, they give you (and your doctor) an evidence-based head start.
So, stay warm, be vigilant, and use your data to get the jump on winter bugs.
Sources and Further Readings:
Fisman D. Seasonality of viral infections: mechanisms and unknowns. Clin Microbiol Infect. 2012 Oct 1;18(10):946–54.
Iacobucci G. Flu in numbers: NHS faces one of worst winters ever, officials warn, amid concern over mutated strain. BMJ. 2025 Nov 12;391:r2391.
Omidi F, Zangiabadian M, Shahidi Bonjar AH, Nasiri MJ, Sarmastzadeh T. Influenza vaccination and major cardiovascular risk: a systematic review and meta-analysis of
clinical trials studies. Sci Rep. 2023 Nov 19;13(1):20235.
Pre-symptomatic detection of COVID-19 from smartwatch data - PubMed [Internet]. Available from: https://pubmed.ncbi.nlm.nih.gov/33208926/
Hasty F, García G, Dávila H, Wittels SH, Hendricks S, Chong S. Heart Rate Variability as a Possible Predictive Marker for Acute Inflammatory Response in COVID-19 Patients.
Mil Med. 2021 Jan 1;186(1–2):e34–8.
