US Flu Season Ends After Intense Winter, Low Vaccine Effectiveness

The United States flu season is drawing to a close after an intense winter marked by a mismatch between the dominant virus strain and available vaccines, leading to one of the lowest vaccine effectiveness rates in two decades, according to federal health data.

The Centers for Disease Control and Prevention reported a continued drop in doctor and hospital visits for flu-like symptoms through the most recent week tracked. High flu activity now affects 16 states, primarily in a region from Colorado to Virginia. Infections peaked in late December, with particularly severe impacts in areas like New York City, where local officials described it as the most intense season in 20 years.

CDC estimates indicate at least 27 million flu illnesses, 350,000 hospitalizations and 22,000 deaths nationwide this season. Those figures compare to 40 million illnesses, 520,000 hospitalizations and a similar number of deaths at this point last year. Among children, at least 101 deaths have occurred, with vaccination status known for most cases; about 85 percent of those children were not fully vaccinated.

Experts attribute the season's challenges to a new variant of the influenza A H3N2 virus, known as...