As norovirus cases rise, here’s what to know about this year’s spread and how to protect yourself
A nasty, highly contagious virus is spreading across the country as the holiday season approaches – and it’s not the flu or Covid.
Norovirus, also known as “winter vomiting sickness,” has been on the rise nationwide since mid-October, particularly in states like Louisiana, Michigan and Indiana, according to data from WastewaterSCAN, an academic program of Stanford University in partnership with Emory University.
With data through Nov. 21, Amanda Bidwell, science program manager for the WastewaterSCAN program, said norovirus concentrations in wastewater have increased 69% nationally since October.
“Right now, we are in the high category for norovirus nationally,” she said. Rates are high in the Northeast and Midwest region, according to wastewater data.
Rates are currently lower than last year, which was largely caused by the GII.17 variant, which may have mutated to become more contagious, experts said. Between August and November 2024, 235 norovirus outbreaks were reported, according to the Centers for Disease Control and Prevention.
There have been 153 outbreaks during the same period this year.
It’s unclear whether the same level of illnesses will persist into 2026, but outbreaks are expected to continue to increase, Bidwell said.
“We have three years of data to kind of show that we have this strong seasonal trend,” she said. “But I can’t say right now how big the peak will be.”
A CDC spokesperson said the agency is closely monitoring norovirus season, which is most common from November to April.
The CDC tracks norovirus through voluntary reporting from clinical laboratories and health departments, but does not currently monitor norovirus in wastewater, which may explain why its tracking does not match WastewaterScan data. People can be sick, but they don’t go to the doctor.
Bidwell said wastewater is an “unbiased way of looking at what’s happening in a community.”
Here’s what you need to know about norovirus and its spread this year.
Norovirus variant becomes more dominant
For more than 30 years, norovirus outbreaks have been dominated by a single strain, GII.4. Last year’s outbreaks were largely caused by the GII.17 variant, accounting for about 75% of outbreaks.
The GII.17 strain has become more prevalent in several countries, including the United States, during the 2020s. The rise in GII.17 could explain why the 2024 peaks and this year’s spread began earlier in October, rather than in winter.
Dr. Robert Atmar, a professor in the Department of Medicine at Baylor College of Medicine, said a combination of factors could have led to GII.17’s dominance.
“The two possibilities are that something in the virus has changed to make it more transmissible, or that there have been changes in the population that have made a greater proportion of people susceptible,” he said. “And it’s probably a combination of both. But I think whether it’s going to persist this year is one of the big questions in our scientific community.”
Dr. Craig Wilen, associate professor of laboratory medicine and immunobiology at Yale University, said GII.17 may not actually be more transmissible, but many people likely have less immunity to the new variant.
“Last year’s GII.17 was probably so effective at infecting so many people because we had much less immunity to it, because it was different enough from the viruses we had been infected with before.”
It’s hard to say how this year’s norovirus season will play out.
Atmar said either variant has a “50/50 chance” of dominating this year, but doesn’t expect the same level of illnesses as last year due to “increased immunity.”
Norovirus symptoms
Norovirus is a highly contagious disease restricted to humans. Norovirus outbreaks can occur anywhere and cause approximately 20 million infections per year. It is responsible for more than half of foodborne illnesses in the United States each year.
It spreads from person to person through vomit or feces that ends up in people’s mouths. It can also be spread through contact with contaminated food, water or surfaces.
The main symptoms are diarrhea and vomiting, earning it the name “two buckets disease.” Other symptoms include fever, stomach pain and body aches.
According to the Mayo Clinic, symptoms such as vomiting and diarrhea may require medical attention in older adults, young children and people with weakened immune systems.
Symptoms usually appear within 12 to 48 hours of exposure and last for a few days. A person can still spread the virus for more than two weeks, even after symptoms disappear.
How to protect yourself against norovirus
Norovirus is notoriously difficult to kill. It is difficult to wash and can survive temperatures up to 145°F. Many scientists call it the “perfect pathogen.”
Wilen said norovirus is “very stable in the environment.”
“It’s highly contagious. Traditional ethanol-based hand sanitizers don’t work as well against this virus as they do other viruses,” the Yale associate professor said.
In order to kill norovirus, the CDC recommends washing hands vigorously with soap, cleaning infected areas with diluted bleach, and washing infected clothing with hot water and detergent. Wearing gloves and disposing of them after cleaning adds protection.
Fruits and vegetables should be properly cleaned, and oysters and shellfish properly cooked, which can also reduce the risk of infection, according to the CDC.
There is no specific treatment for norovirus, but rehydration is essential to replace lost fluids.
Although there is currently no vaccine for norovirus, a Phase 3 Moderna trial is in place.
