The flu is continuing to cause widespread illness across the United States, with all but four states reporting high or very high levels of activity as a new strain, known as subclade K, spreads rapidly.“This is absolutely a standout year,” said Dr. Caitlin Rivers, an epidemiologist and senior scholar at the Johns Hopkins Center for Health Security, as per CNN. “It’s the worst flu activity we’ve seen in at least two decades. Most of the country is experiencing extremely high levels, and we are still very much in the middle of it.”She added that it is unusual to see such a severe flu season follow another difficult year, as intense seasons do not typically happen back to back.U.S. Sees Worst Flu-Like Illness Levels In 25 YearsAcross the country, about 8.2 percent of all doctor visits during the final week of the year were for flu-like symptoms. At the same time last season, which was also considered severe, that figure stood at 6.7 percent.In Massachusetts, where flu activity is rated as very high, health officials urged residents to get vaccinated as soon as possible.Experts stressed that vaccines remain the most effective tool available. “They prevent severe illness and hospitalization, and they save lives. If you have not yet received a flu or COVID-19 vaccine this season, now is the time. It is not too late. Getting vaccinated protects not just you, but also your family, friends, colleagues, and the wider community.”Nearly All States Report High Flu ActivityThe latest CDC data shows that almost every state is experiencing high or very high flu activity. Montana and Vermont reported low levels, while South Dakota and West Virginia were at moderate levels. Nevada did not submit flu data this week, but last week’s report showed high activity there as well.When it comes to severity, measured by hospitalizations, this flu season has not yet reached record levels. However, the cumulative hospitalization rate is already the third highest for this point in the season since 2010–11, and experts warn that could rise as infections continue.Experts Urge Immediate VaccinationDr. Michael Osterholm, who leads the Center for Infectious Disease Research and Policy at the University of Minnesota, urged people to act quickly.“If you haven’t been vaccinated, do it within the next 48 hours. Don’t put it off,” he said. “You may still be able to protect yourself from the later stages of the season, but it takes about seven to 10 days for the body to build immunity after vaccination. There’s very little time to waste.”The CDC estimates that at least 11 million people have been infected with the flu so far this season. Around 120,000 have been hospitalized, and 5,000 people have died.Child Deaths and Falling Vaccination RatesThe agency also confirmed another child death linked to influenza, bringing the total number of pediatric flu deaths this season to nine.At the same time, flu vaccination rates among children have dropped sharply. Coverage has fallen from 53 percent during the 2019–20 season to 42 percent at the same point this year.The new flu data was released on the same day the US Department of Health and Human Services announced plans to revise the childhood vaccine schedule. The proposed changes would recommend flu shots for children only after consultation with a healthcare provider, a process known as shared clinical decision-making. Critics worry this could make vaccines harder to access.“To pull back on flu recommendations during a season this severe feels deeply out of touch,” said Dr. Sean O’Leary, chair of the American Academy of Pediatrics’ Committee on Infectious Diseases. “That comes after a year in which we saw the highest number of childhood flu deaths in many years.”Adult Vaccination Also DeclinesVaccination rates have also dropped among adults. CDC data shows that nearly 61 million adults received a flu shot during the 2019–20 season. This year, that number has fallen to about 48 million.Rivers said she does not believe lower vaccination rates are the main reason for the surge in cases.“The flu vaccine is not primarily meant to stop infection or transmission,” she explained. “Its main role is to prevent severe illness.”New Flu Strain Drives the SurgeInstead, experts point to the emergence of the new subclade K strain, which now accounts for most flu samples analyzed in laboratories.Rivers said the strain appears different enough from past flu viruses to bypass existing immune protection in many people. Subclade K began spreading after scientists had already selected the strains used for this year’s flu vaccines. As a result, the shots likely provide only partial protection against it.“I think this virus has real staying power,” Osterholm said, as per CNN, noting similar patterns in Australia, Japan, and parts of the United Kingdom. “We’re likely to see significant community spread for at least another three to four weeks.”