New Flu Strain Triggers Early Surge Across U.S., Prompting Closures and Masking

An unusually early surge in influenza is rippling across the United States, driven by a new H3N2 subclade K strain that health officials say is spreading faster than a typical flu season. The latest CDC data dated December 6 show very high transmission in New York City, with high activity in surrounding New Jersey and New York state, and elevated levels in Colorado and Louisiana. Idaho and Connecticut are listed as moderate. The subclade K is on the rise in more than three dozen states.

In New York City, acting health commissioner Dr. Michelle Morse said the city’s cases are rising quickly and urged residents to get their annual flu shot and to wear a mask if symptoms develop. In Brooklyn, Poly Prep Country Day School’s Dyker Heights campus closed for two days after at least 200 students were absent or sent home with flu or flu-like symptoms. Earlier this month, health systems in New Jersey reinstated masking protocols for patients, visitors and workers; Detroit Medical Center restricted visitor access to protect patients and staff.

In Hawaii, the Department of Health reported a rise in 911 calls for respiratory-related and flu-like symptoms, with 332 respiratory-related encounters recorded for the week ending December 4, about a 45% increase from June. Nationwide, roughly 3 million people have contracted the illness so far, and there have been about 1,200 deaths this season. The CDC data show an influenza hospitalization rate of 6.9 per 100,000 people, up from 4.3 per 100,000 the previous week. The share of flu tests that are positive rose to 8.1% for the week ending December 6, from 7.1% the week before; the rate of outpatient respiratory illness also rose, to 3.2% from 2.9%.

Texas health officials said the week ending December 6 was the third in a row to surpass 5,000 hospital and clinic visits for flu-like illness, and 7.4 per 100,000 people over age 65 were hospitalized, compared with 2.2 per 100,000 last month. In Iowa, the Moulton-Udell school district canceled classes and sports after nearly 30% of students and staff fell ill, and in Missouri, Villa Duchesne Catholic School in St. Louis canceled classes for several days due to high flu activity. In Michigan, Detroit Medical Center recently tightened visitor limits to reduce exposure in facilities still trying to cope with surges.

Public health officials say this year’s dominant flu strain is a new variant that is not well recognized by people’s immune systems, which could increase the risk of severe illness and hospitalization, especially among vulnerable groups. Influenza A continues to account for about three of every four flu cases, and vaccination remains the best available defense. The seasonal vaccine typically shows an effectiveness range of about 40% to 60% against circulating strains. Officials note that flu symptoms can come on abruptly and include fever, fatigue, chills, headache, body aches, congestion, runny nose and coughing. The disease can disrupt schooling and work, underscoring the importance of vaccination and early treatment when symptoms appear.

In the latest national assessment, the CDC said seasonal influenza activity continues to rise across most parts of the country, though severity indicators remain low and the flu season is still in its early stages. By now this season has seen about 3 million cases and 1,200 deaths, with a higher hospitalization rate than at the same point last year, when the weekly test positivity was 5.1% and hospitalizations were 3.1 per 100,000. The season typically peaks between December and February after the winter holidays.