Last winter's norovirus season was ugly enough that it produced a year of headlines about a stomach bug tearing through cruise ships, nursing homes and school cafeterias. This season, the same surveillance system counted fewer than half as many outbreaks.
Between August 1, 2025 and May 7, 2026, state health departments participating in CDC's NoroSTAT network reported 1,194 norovirus outbreaks. In the same window a year earlier, those states reported 2,534.
The more useful sentence is CDC's own framing of what that means. The agency says the 2025-2026 total sits "within the middle 50% of outbreaks (interquartile range)" reported in the same period across the 2012 through 2025 seasonal years.
In other words, this is not a good season. It is an ordinary one. The season that felt catastrophic was the abnormal data point, and reading this year's decline as improvement gets the baseline backwards.
What NoroSTAT Actually Counts
The number is easy to misread in two directions, so the method matters.
NoroSTAT is a sentinel network, not a national census. Fourteen state health departments report through it: Colorado, Massachusetts, Michigan, Minnesota, Nebraska, New Hampshire, New Mexico, North Carolina, Ohio, Oregon, South Carolina, Tennessee, Virginia and Wisconsin. Those states are not the country, and the composition changes. New Hampshire appears in the current season's list where Alabama appeared previously, which means year-over-year comparisons carry a small caveat built in.
It counts outbreaks, not cases. CDC defines a norovirus outbreak as two or more similar illnesses from a common exposure, suspected or laboratory-confirmed. One outbreak in a nursing home can involve dozens of people. One outbreak at a wedding can involve two.
It counts reported outbreaks, which is a function of whether someone investigated. An outbreak in a facility with an infection preventionist gets reported. The same cluster among a group of friends does not.
Nationally, CDC estimates roughly 2,500 reported norovirus outbreaks a year and about 19 to 21 million illnesses, 109,000 hospitalizations and 900 deaths annually. Those national figures dwarf the sentinel count and are the right scale for understanding the burden.
Reporting also lags. Participating states have seven business days to report; data are updated monthly, and the seasonal year runs through July 31. The figures here run through early May, so the season is not formally closed.
Why Last Season Was the Outlier
The 2024-2025 season stood above the range CDC had recorded across more than a decade, and the explanation researchers offered at the time was a strain change rather than a change in the virus's severity.
A genotype called GII.17 displaced the long-dominant strain, rising from a small share of outbreaks to roughly three-quarters of them. Jan Vinjé, who heads CDC's CaliciNet laboratory network, said at the time that it was too early to know whether the strain caused more severe illness and that "likely lower population immunity is the reason for the early surge."
That is the standard mechanism. When a new genotype becomes dominant, the accumulated immunity in a population no longer matches the circulating virus well, more people are susceptible, and outbreak counts rise. As immunity catches up over a season or two, counts typically settle back toward the historical range, which is what the current data appear to show.
This also means the decline is not evidence that anything was done differently. It is largely a consequence of a population that has now met GII.17.
What This Changes for Households
Practically, very little, and that is worth saying plainly rather than dressing the number up as good news.
Norovirus remains the leading cause of vomiting, diarrhea and foodborne illness in the United States. Most outbreaks occur in long-term care facilities, followed by restaurants, schools, child care centers and occasionally cruise ships. A typical season still produces thousands of outbreaks nationally.
The prevention advice does not change with the outbreak count, and one piece of it is regularly gotten wrong. Alcohol-based hand sanitizer is not reliably effective against norovirus. Handwashing with soap and running water for at least 20 seconds is what works, particularly after using the bathroom and before preparing food.
The virus is unusually durable on surfaces and resistant to many common disinfectants. Cleaning after a vomiting or diarrhea incident calls for a bleach-based product or an EPA-registered disinfectant labeled effective against norovirus, and contaminated laundry should be handled with gloves and washed on the longest hot cycle.
People are contagious from the onset of symptoms and for at least two days after recovery, and often longer. That is why food handlers should not return to work immediately after feeling better, and why anyone caring for a person in a household should keep washing hands well past the point the vomiting stops.
Dehydration is the real danger, and it falls hardest on young children, adults over 65, and people who are immunocompromised. Signs that warrant medical attention include little or no urination, dizziness on standing, dry mouth and throat, unusual sleepiness or confusion, and in children, a lack of tears when crying.
What Happens Next
The seasonal year closes July 31, and CDC updates NoroSTAT monthly, so a full-season figure should follow. CaliciNet publishes the circulating genotype distribution separately, and whether GII.17 remains dominant or another genotype starts gaining share is the variable most likely to determine what next winter looks like.
Wastewater surveillance now provides an earlier signal than outbreak reports do, and it tends to move weeks ahead of the outbreak count.
The confirmed finding is that sentinel-state outbreak reports fell from 2,534 to 1,194 year over year and now sit inside the normal historical range. The people most affected by norovirus remain residents of long-term care facilities and the very young and very old. The most useful action is soap and water rather than sanitizer. The central uncertainty is which genotype dominates next season.
Frequently Asked Questions
How many norovirus outbreaks were reported this season? NoroSTAT states reported 1,194 outbreaks between August 1, 2025 and May 7, 2026, compared with 2,534 in the same period a year earlier.
Is that a good sign? It is a normal one. CDC says the current total falls within the middle 50 percent of outbreaks reported over the 2012 through 2025 seasons. Last season was unusually high.
Is this a national count? No. NoroSTAT is a 14-state sentinel network. CDC separately estimates roughly 2,500 reported norovirus outbreaks nationally each year.
Why was last season so bad? A genotype called GII.17 became dominant, and lower population immunity to that strain was the leading explanation offered by CDC researchers.
Does hand sanitizer work against norovirus? Not reliably. Wash hands with soap and running water for at least 20 seconds.
How long am I contagious? From the start of symptoms until at least two days after recovery, and sometimes longer. Food handlers should not return to work as soon as they feel better.
When should I seek care? For signs of dehydration, including little or no urination, dizziness on standing, dry mouth, unusual sleepiness or confusion, or no tears when a child cries.
