After a relatively slow start to the respiratory virus season, COVID-19 levels in the United States began ramping up just ahead of the winter holidays.Video above: Experts offer tips on staying healthy for the holidaysIn previous years, COVID-19 levels have typically started to rise in early November and reach their seasonal peak by the end of December. But this year, levels were nearly the lowest they바카라 게임 웹사이트�ve ever been through October and all of November, according to wastewater surveillance data from the U.S. Centers for Disease Control and Prevention.Trends started to shift in early December, though, with levels rising from low to high by the middle of the month. In the week ending on Dec. 21, there was nearly three times as much COVID-19 circulating in the U.S. than there was during the week ending Dec. 7, CDC data shows.This surge happened in all regions of the country, but there has been a particularly sharp uptick in the Midwest, where COVID-19 levels are nearly twice as high as they are in other parts of the country.Some experts worry that the rapid rise after an unusually long lull could have left many people vulnerable to disease spread at the height of the holiday season.In a social media post in mid-December, Dr. Michael Hoerger, a researcher at the Tulane University School of Medicine, called the latest wave of COVID-19 transmission a "'silent surge,' coming on late out of nowhere."Hoerger runs a COVID-19 forecasting model that draws heavily from the CDC wastewater surveillance data. His estimates suggest that without any testing or isolation policies in place, there was a 1 in 8 chance of COVID-19 exposure at a gathering of 10 people on Christmas Day. On a plane of more than 100 people, there was a 3 in 4 chance of exposure.The rapid rise in cases corresponds with a newly dominant coronavirus variant called XEC.XEC is a hybrid of two JN.1 variants, which was the Omicron subvariant that accounted for most cases during last winter바카라 게임 웹사이트�s surge, according to the CDC. Agency data shows that the XEC variant has been circulating in the US for months but overtook one of the so-called FLiRT variants 바카라 게임 웹사이트� KP.3.1.1 바카라 게임 웹사이트� between the end of November and the first week of December. From Dec. 8 to 21, XEC accounted for 45% of new cases, up from 15% of cases two months earlier.Variants are expected to be "gradual changes to the virus, known as mutations, result in new viruses that look different to your immune system," the CDC says. But this novelty is what makes it easier for variants to escape your immunity and make you sick.Video above: Keep an eye on that cough after you see friends and family over the holidaysThe currently circulating variants are similar enough to each other that the latest COVID-19 vaccines are still expected to be effective against severe illness or death, but vaccination rates are lagging. Only about 21% of adults and 10% of children have gotten their COVID-19 vaccine this season, according to CDC estimates.Despite COVID-19's slow start, the latest forecasts from the CDC's official models predict that there could be as many hospitalizations for respiratory viruses as there were last year.Overall, respiratory virus activity in the US is high. Flu levels had been high and rising for a few weeks before COVID-19 levels started to rise, and RSV levels are increasing, too. According to CDC data, there were about 6 respiratory virus hospitalizations for every 100,000 people in the US during the third week of December, twice as many as a month earlier.And outbreaks of some other contagious diseases 바카라 게임 웹사이트� including whooping cough and norovirus 바카라 게임 웹사이트� are worse than they바카라 게임 웹사이트�ve been in more than a decade.Norovirus is a common and very contagious virus that causes gastrointestinal symptoms. There have been nearly 500 outbreaks reported since August, according to CDC surveillance systems, a third more than this time last year.Whooping cough, also known as pertussis, is a very contagious respiratory illness. For many, the bacterial infection starts with symptoms similar to the common cold 바카라 게임 웹사이트� a runny nose, sneezing, a low-grade fever and a tickly cough 바카라 게임 웹사이트� but a painful, full-body cough can develop after a week or two. These coughing fits can be so severe that they cause patients to vomit or break ribs, and they바카라 게임 웹사이트�re often accompanied by a whooping sound as the person tries to catch their breath.Although whooping cough can be serious for all ages, children younger than 1 are particularly sensitive because their immune systems are still developing. This is especially true for infants and young children who haven't had all their recommended vaccines.There have been more than 32,000 cases reported this year, according to preliminary data from mid-December 바카라 게임 웹사이트� about six times more than there were at this time last year and more than there have been since 2014.Children now have the highest rate of emergency department visits for flu and RSV, according to the latest CDC data. Visits for COVID-19 are most common among seniors, followed closely by children younger than 5.