A young woman experiences stomach discomfort.gettyOutbreaks of highly contagious norovirus are up in the U.S. Also known as the "winter vomiting bug" or "stomach flu," the seasonal illness is at its highest recorded level this time of year for more than a decade.Officials reported 91 suspected or confirmed norovirus outbreaks over the first week of December. This is the highest level seen at this time of year since at least 2012, and one of the highest case loads reported at any time of year over the last 12 years.As this Centers for Disease Control and Prevention data only currently covers 15 states, it doesn't give a comprehensive picture of norovirus across the country. Increasing numbers of cases may be influenced by more states joining the program over the years.Nonetheless, it reflects peaks and trends in the spread of the virus, which usually circulates more widely between November and April every year. The U.S. reports around 2,500 outbreaks a year, typically peaking in February.This year, it appears its hitting harder, earlier, possibly as more people get together "for the first time in several years," experts told Fortune magazine.MORE FOR YOURise In Seasonal IllnessesMany countries are seeing an uptick in several seasonal viruses as people mingle more over the holidays than they did during the pandemic. Diseases like flu and respiratory illness RSV are all on the up and, although it doesn't represent the same threat it once did, COVID-19 is circulating widely. Relatively high levels of whooping cough, which can be deadly for infants, are also of concern to public health experts.Countries like the U.K. have issued numerous public statements to encourage members of the public to get vaccinated against illnesses and practice everyday hygiene measures to prevent the spread of contagious diseases.Officials in the country's public health system says they're battling a "quad-demic" of flu, COVID-19, RSV and norovirus, with 95% of England's hospital beds full by early December.What Is Norovirus?Norovirus is the most common cause of vomiting, diarrhea, and foodborne illness in the U.S. Although it's often referred to as "stomach flu," it's not related to influenza.The virus spreads via tiny particles of infected fecal matter that enter the mouth. This means you can catch it by eating or drinking something contaminated with the virus and by touching your mouth after you've touched a contaminated surface like a doorknob. If you're looking after someone with the disease, it can be easy to catch it yourself.Norovirus often causes vomiting, nausea, diarrhea and stomach pain, but may also result in fever, headaches and body aches. It can be very unpleasant, but most people will recover within about three days of developing symptoms.It's important to drink water if you catch norovirus, as both vomiting and diarrhea can cause dehydration. If you suspect someone with norovirus has severe dehydration, seek medical help.How Can I Protect Myself Against Norovirus?You can protect against norovirus with vigilant hand-washing. Regularly wash your hands with soap and warm water for at least 20 seconds, especially after using the bathroom, changing a baby's diaper, shaking someone's hand or caring for someone with the disease.Don't share food or drinks with a person infected with the disease, and make sure to wash any potentially contaminated sheets and clothes in hot water.Washing fruit and vegetables and cooking seafood thoroughly will help prevent the virus spreading through food.If you catch norovirus, you can protect others by staying at home for two days after your symptoms stop. You can pass on the disease for two weeks after your symptoms resolve, so make sure to keep washing your hands regularly.Is There A Vaccine For Norovirus?Unfortunately, there's currently no vaccine against norovirus. But researchers at Moderna are recently started trials of a candidate shot that may one day offer protection.Vaccines are the best way to prevent against several other seasonal illnesses, as well as other diseases like whooping cough and measles that are on the rise in the U.S.Flu vaccines are available every year during fall. They are recommended annually for almost everyone over the age of 6 months, and are especially important for people at risk of severe disease, which hospitalizes betwen 140,000 and 710,000 Americans and tragically kills an estimated 12,000 to 51,000 every year.RSV vaccines are available for older people and pregnant people, who can confer protection on to their vulnerable infants.COVID-19 vaccines are recommended annually for anyone aged 6 months or older. They are particularly important for older adults, people at risk of severe disease, and people who have never had a vaccine.Full details of each vaccine are available on the CDC website.