Flu season: Stanford expert explains the subclade K strain

Stanford Medicine's Yvonne Maldonado says the current U.S. flu season shows unusually early and high activity driven by an H3N2 variant called “subclade K,” and CDC data cited in the article report about 11 million infections so far.

Flu activity in the United States is higher than in many recent seasons and began earlier than usual. The article quotes Stanford Medicine’s Yvonne Maldonado, who describes the dominant strain as a variant of influenza A H3N2 called “subclade K.” The piece notes that this strain appears to evade some immunity from the current vaccine, while the vaccine still offers some protection. National data cited in the article show widespread activity across most states and substantial hospitalizations and deaths this season. Key details: - Reported national totals in the article include about 11 million infections, 120,000 hospitalizations and 5,000 deaths, with 45 states at high to very high activity levels. - The dominant virus is described as an H3N2 variant labeled “subclade K,” which the article says has mutations that reduce—but do not eliminate—vaccine-derived immunity. - The article cites CDC guidance that annual influenza vaccination is recommended for people six months and older and notes that vaccines have prevented large numbers of illnesses and hospital visits in prior seasons. - The article says those in higher-risk groups (people 65 and older, children under 2, people with certain chronic conditions, pregnant people, residents of long-term care) are more likely to experience severe outcomes, and it reports that antiviral treatments can help when given early. Summary: The article presents a picture of an unusually active and early flu season linked to the H3N2 “subclade K” variant and reports substantial national impacts to date. How the season will evolve beyond current activity is undetermined at this time.