There are two subtypes of type A flu, and subclade K is a mutated version of one of them, named H3N2. Scientists believe the subclade K virus is a shape-shifter, constantly mutating, and it comes in multiple forms. The CDC says only about 42 per cent of adults and children have gotten a flu vaccination so far this year. That variant, known as subclade K, has led to early outbreaks in the UK, Japan, and Canada. Learning how it compares to COVID and other seasonal illnesses can help you make informed decisions. Subclade K is part of a broader trend of evolving respiratory viruses.
Influenza, also known as the flu, is a contagious respiratory illness caused by influenza viruses, according to the Centers for Disease Control and Prevention. Since the flu season began in October, at least 7.5 million people have contracted the illness, USA TODAY reports. The mutated strain, known as subclade K, originates from the most common flu-causing virus, influenza A, and one of its most common variations, H3N2. According to an update Monday, flu activity in the state has climbed to “very high” levels in recent days, the most severe of five categories of respiratory illness activity used by the CDC.
What is Subclade K? What to know about ‘super flu’ strain and its symptoms
Influenza season normally peaks in mid-to-late winter, from around December through February. Because it’s structurally distinct, subclade K may also be better at evading immune systems that have already developed protection against more familiar strains. According to the CDC’s FluView Interactive Map, which monitors visits for respiratory illness with fever plus a cough or sore throat, Florida is seeing high activity. Hospitalizations nearly doubled in just one week, climbing to 19,053 from 9,944 the week before, based on CDC data.
How long is flu contagious?
The most effective way to prevent serious illness from flu is vaccination, according to the World Health Organization, CDC and other leading medical institutions. Mask-wearing while sick or out and about during illness season can also help to prevent the spread. The last available tracing data from the CDC found that 91% of the 600 U.S. flu cases that were tested between Dec. 22 and 28 were caused by H3N2.
Warning signs to watch for
Flu season typically peaks mid-to-late winter, from around December through February. Flu season typically starts around late September or early October, when the weather begins to cool down, and usually lasts until the following summer, in May. Your eligibility for YouTube Recap depends on several requirements regarding your account activity and settings.
However, it is still not too late to get a flu shot, which, according to the doctors, can still prevent severe illness even if someone gets infected. Even when vaccines are not an exact match, they still reduce the risk of severe illness, hospitalization, and flu-related complications. Because international travel plays a major role in virus spread, experts expect Subclade K to continue appearing in new locations as the flu season progresses. Some countries have reported that this strain is becoming more common than other circulating flu viruses. Understanding the subclade K flu strain, how it spreads, and what symptoms to watch for can help you take the right precautions.
Does subclade K make people sicker?
Most people who get the flu will recover in a few days to less than two weeks. The CDC reports that people with the flu are most contagious during the first three days of their illness. Subclade K is a variant of the H3N2 virus, which is a subtype of influenza A. Influenza A(H3N2) viruses are the most frequently reported flu viruses this season.
How long does the flu last?
- The CDC recommends everyone 6 months and older receive a flu vaccine.
- Subclade K – which has spread to most parts of Europe as well – was first detected in Norway, followed by the UK, where the influenza season started 4 to 5 weeks earlier than usual.
- Doctors say it causes extremely high fever, along with signs of a cold and flu.
- Japan also witnessed an early start, as the levels of H3N2 flu are now plateauing and may soon start to drop.
- Subclade K is a newly emerged subgroup of a well-established human seasonal flu virus known as the H3N2 influenza A virus, which has circulated for decades.
The Centers for Disease Control and Prevention estimates that there have been at least 4.6 million illnesses, 49,000 hospitalizations and 1,900 deaths from flu so far this season. The CDC recommends everyone 6 months and older receive a flu vaccine. The new strain, called subclade K, has made its way to the U.S. after spreading quickly through countries such as the UK, Canada and Japan. That H3N2 strain is always harsh, especially for older adults.
Content included & excluded from Recap
Last week, the Centers for Disease Control and Prevention reported high or very high levels of illness among people, mostly youngsters. Cases of the flu are rising rapidly across the United States, driven by a new variant of the virus, gripping more than half of the states, even as holiday travel plays out. Early antiviral treatment may help shorten illness duration and reduce complications, especially when started within the first two days of symptoms. If you develop flu symptoms, stay home, rest, and contact a healthcare provider if symptoms worsen or if you are in a high-risk group. One of the most common questions is whether the flu vaccine still works against this new flu variant 2026. Children and people with asthma, heart disease, or weakened immune systems are also at higher risk for severe illness.
It’s also important to wash them before and after eating, before and after handling food, after using the bathroom and after being around sick people or touching surfaces that could be contaminated. This applies to all the ailments above and others that often circulate during the wintertime, like respiratory syncytial virus, or RSV. As of Dec. 30, CDC projections found that flu infections are on the rise in 17 states, unchanged or not reported in seven states and declining or likely declining in 24. Some people, like young children and those with weakened immune systems, may be contagious for longer, however. According to the CDC, the warning signs are different in children and adults.
- The CDC says only about 42 per cent of adults and children have gotten a flu vaccination so far this year.
- Flu season typically starts around late September or early October, when the weather begins to cool down, and usually lasts until the following summer, in May.
- Each year, the seasonal flu shot is formulated to target the strains most commonly circulating.
- Although the vaccine is not an exact match, experts say it will still offer protection against the influenza virus.
The effectiveness of the vaccine varies depending on how closely the virus strains in the vaccine match those currently circulating. A new strain of the flu is causing concerns for the rest of the winter season. According to the CDC, there have been at least 7.5 million illnesses in the US, 81,000 hospitalisations, and 3,100 deaths from flu so far this season.
CDC data through Dec. 27 showed that just under 33% (23,350) of the 70,757 flu tests administered that week were reported positive to the National Respiratory and Enteric Virus Surveillance System. Flu cases have skyrocketed since December began, according to CDC data, and flu activity is vegas casino download now categorized as “high” nationwide. Flu can be detected in infected persons at least one day before symptoms begin, and up to seven days after, but those with flu are most contagious around three days into their infection, according to the CDC. “Vaccinations remain the most effective tool to prevent severe illness from flu, COVID-19 and RSV.”
“Again, we recommend wearing a mask around anybody who’s vulnerable or if you’re in a crowded place for that first seven days. And, you know, absolutely great hand washing hygiene so you’re not spreading the virus around. And if you can stay in, stay home.” “It’s about five to seven days from the symptom onset before you stop really shedding high levels of the virus. So 10 days is perfect, but it really doesn’t need to be that long,” Loafman said. Flu symptoms typically begin within one to four days of exposure, according to the Cleveland Clinic. In Chicago, residents can get a flu shot by visiting any one of the city’s immunization clinics. “I kept putting it off and I wish I hadn’t because both my parents who I live with right now had the flu shot and didn’t get sick, luckily,” she said.
When doctors describe Subclade K as severe, they are not suggesting it is a completely new or unknown virus. This global pattern is one reason public health officials are taking the variant seriously. Early data suggests this variant has accumulated mutations that may help it spread more easily or partially evade existing immunity. When these changes add up, they can create a new subclade that behaves differently from earlier strains. A flu virus infection of the respiratory tract can trigger an extreme inflammatory response in the body, leading to sepsis. Pneumonia is a serious complication resulting from either flu virus infection alone or the co-infection of flu virus and bacteria, according to the CDC.
There are no rules about when you can or can’t get a vaccine, but professionals typically recommend getting your shot in September or October. “The flu reporting year uses standard reporting weeks outlined by the Centers for Disease Control and Prevention (CDC), where every year has 52 or 53 reporting weeks. It can last from a few days to two weeks, according to the Cleveland Clinic. According to the CDC’s FluView Interactive Map, which monitors visits for respiratory illness with fever plus a cough or sore throat, Florida is seeing low activity. H3N2 symptoms include fever, chills, body aches, headache, extreme fatigue, congestion or runny nose, and coughing.
What are the symptoms of the flu?
Illinois also on Monday reported its first influenza death in a child this season. Already the Illinois Department of Public Health and numerous health departments across Chicago-area counties have issued warnings as hospital admissions and positive tests for influenza soar in the state. “More fever with the flu this year than people are accustomed to. And the fever can last up to seven days, so five to seven days. And that’s worrisome,” Dr. Mark Loafman, the chair of Family and Community Medicine at Cook County Health, told NBC Chicago. As cases reach “very high” levels in Illinois, a mutated and highly contagious variant known as “subclade K” has brought a change in telltale signs of the virus, experts have said.
“For most people who need only one dose of influenza vaccine for the season, September and October are generally good times to be vaccinated against influenza,” the CDC says. A new strain of influenza has surged across the country during an already busy travel season, with experts worried that low vaccination rates could lead to a significantly brutal flu season. Although the vaccine is not an exact match, experts say it will still offer protection against the influenza virus. While overall influenza activity across the U.S. remains relatively low, it is increasing among children and young adults, according to the latest report from the Centers for Disease Control and Prevention.
“Illinois is facing a significant winter surge in seasonal respiratory illnesses with flu activity at very high levels,” Dr. Sameer Vohra, IDPH director, said in a statement. “These are contagious viruses and people are indoors and we’ve had a lot of holiday travel and people together. So we would expect this spike would continue over the next few weeks,” he said. Everyone 6 months and older is eligible for the flu vaccine unless they have a specified medical condition, such as an allergy to its ingredients or a previous severe reaction to the shot. Though flu season ends May 17, 2025 (week 20), surveillance continues year-round,” the Florida Department of Health’s website says. Dubbed the “super flu,” it is a variant of influenza A H3N2 in subclade K, which was responsible for outbreaks in the United Kingdom and Japan. According to Today.com, scientists caught the H3N2 subclade K too late to update the vaccine for this season.
Japan also witnessed an early start, as the levels of H3N2 flu are now plateauing and may soon start to drop. Doctors say it causes extremely high fever, along with signs of a cold and flu. But they are different enough to evade some of the protection from this year’s vaccine. Subclade K’s mutations are not enough of a change to be considered an entirely new kind of flu. That includes at least eight child deaths and is based on data as of Dec. 20, before major holiday gatherings.