Respiratory illness in the United States
The three major respiratory pathogens side by side — influenza, COVID-19, and RSV — based on CDC NHSN weekly hospital admission rates.
Current situation: Influenza
In week 15 of 2026, activity of influenza (seasonal flu) in the United States is low. The trend — derived from weekly hospital admission rates — is falling. Over a four-week comparison, a clear decline is visible.
The classification is based on the CDC's NHSN weekly hospitalization data and the FluView surveillance report. Seasonally, infection waves in the United States typically peak between December and February; activity is usually markedly lower during the summer months. How severe a given season becomes depends on the circulating virus variant and the population's immune status, among other factors.
Current situation: COVID-19
In week 15 of 2026, activity of COVID-19 in the United States is low. The trend — derived from weekly hospital admission rates — is falling. Over a four-week comparison, a clear decline is visible.
The classification is based on CDC NHSN weekly confirmed COVID-19 hospital admissions per 100,000 population. Seasonally, infection waves in the United States typically peak during winter, with frequent summer waves driven by new variants; activity is usually markedly lower in late spring between waves. How severe a given season becomes depends on the circulating virus variant and the population's immune status, among other factors.
Current situation: RSV
In week 15 of 2026, activity of respiratory syncytial virus (RSV) in the United States is low. The trend — derived from weekly hospital admission rates — is falling. Over a four-week comparison, a clear decline is visible.
The classification is based on CDC NHSN weekly RSV hospital admissions and the RSV-NET surveillance system. Seasonally, infection waves in the United States typically peak between November and February; activity is usually markedly lower in spring and summer. How severe a given season becomes depends on the circulating virus variant and the population's immune status, among other factors.
Data sources and methodology
The current picture for the United States is built on the CDC's National Healthcare Safety Network (NHSN) weekly hospital admissions data. NHSN collects laboratory-confirmed admission rates per 100,000 population for influenza, COVID-19 and RSV, submitted by participating hospitals nationwide. We rescale these hospitalization rates into a consultation-equivalent signal so the qualitative “low / moderate / high” categories are consistent with how we report other countries.
CDC NHSN (Hospital Respiratory Data)
NHSN is the CDC's national surveillance system for healthcare-associated infections. Since 2022, hospitals report weekly counts of confirmed influenza, COVID-19 and RSV admissions. We use the jurisdiction-level USA rates (admissions per 100,000 population per week), which give an unbiased picture of severe illness pressure on the healthcare system.
CDC FluView
CDC FluView is the long-running weekly flu surveillance report, drawing on outpatient ILI visits via the ILINet sentinel network, public health laboratory results, and hospitalization data. While our headline level is driven by NHSN, FluView provides the context for how a season compares to the typical seasonal curve.
Why hospitalization rates
Unlike clinic visits or self-reports, hospital admissions remain reliable across changes in testing behaviour and reporting practices. They reflect severe outcomes — the load that matters most for health-system capacity — and are reported with a roughly one-week lag.
Qualitative classification
The “low”, “moderate” and “high” categories follow seasonal reference values and epidemiological thresholds calibrated to match our classifications for other countries. Hospitalization rates are scaled to consultation-equivalent incidence using pathogen-specific conversion factors derived from typical seasonal peaks in both systems. Data refreshes weekly when the CDC publishes the latest NHSN update, typically late in the week.
Frequently asked questions
How many people are currently sick with respiratory illnesses in the US?
The CDC does not publish a single national “how many are sick” figure, but weekly hospital admission rates for flu, COVID-19, and RSV together give a strong proxy. When all three are active at once — as often happens between December and February — the combined respiratory-illness burden can strain hospital capacity. On infectrisk.com we classify the overall picture as low, moderate, or high based on these hospitalization signals. For exact figures and personalized risk, the InfectRisk app provides deeper analysis.
What is the “tripledemic”?
“Tripledemic” is the media shorthand used during the 2022–2023 winter for the simultaneous peak of influenza, COVID-19, and RSV — the first season in which all three were circulating at high levels at the same time post-pandemic. Since then, the three viruses regularly co-circulate during the US winter respiratory season, though the intensity of any given season varies.
Why do respiratory illnesses peak in winter?
Several factors drive the winter peak. Many respiratory viruses survive longer in cold, dry indoor air, and heated buildings create the dry conditions that impair the protective function of airway mucous membranes. People spend more time indoors in close contact, and lower humidity favors aerosol transmission. On top of that, the start of school and holiday gatherings mix populations more intensely during the colder months.
What is “immune debt” and does it explain recent severe seasons?
“Immune debt” refers to the idea that, after periods of low pathogen circulation — for instance during COVID-19 lockdowns — population-level immunity to certain viruses declines. Subsequent waves can then hit harder because regular immune “training” was missing. This concept partly explains the unusually severe RSV and flu seasons seen in 2022–2023. It is not a permanent immune defect, just a temporary catch-up.
How does the CDC decide when an activity level is “high”?
The CDC uses historical baselines and defined thresholds. For influenza-like illness, the CDC compares current outpatient visits against the average for past non-epidemic weeks. For hospitalizations, threshold crossings into the high range reflect weekly admission rates above past severe-season reference points. These data-driven classifications help distinguish unusual surges from normal seasonal activity.
Want the actual numbers?
You'll find them in the app.
Here you only see the trend. In the app: exact incidence rates, “X out of 100 people infectious”, your personal risk based on age and pre-existing conditions, wastewater trends, 36 countries, home-screen widget.
