Flu cases already increasing across the US: Is this year’s shot effective?

Flu activity is rising early

The flu season is gathering pace earlier than is typical this year. CDC data show positive flu tests increased 30 percent in the past week, and the agency says H1N1 is causing the most illnesses this season.

Flu season generally begins in September or October and continues into April or May. Doctors say it is still worthwhile to get vaccinated now.

What is known about the shot

Early evidence suggests this year’s vaccine is a good match for a circulating variant. But less is known about how well it works against H1N1, Scott Hensley, a University of Pennsylvania microbiology professor, told NBC News on Friday.

The vaccine prompts the immune system to develop protective antibodies, a process that takes about two weeks. Those antibodies target three seasonal viruses.

Protection against severe illness

Even when vaccine protection is incomplete, vaccination can help prevent severe illness and death. The CDC estimates that flu causes 9.4 million to 51 million illnesses and about 6,300 to 52,000 deaths each year. Dr. Ryan Stanton, president-elect of the American College of Emergency Physicians, said in a recent briefing, according to AARP, “It’s not just a cold.”

Vaccination rates have declined

In the most recent season reported by the CDC, 2024-2025, 41.9 percent of adults received a flu shot. That was the lowest adult vaccination rate in seven seasons, despite wider availability. Experts cite vaccine hesitancy and misinformation about the virus and vaccine as contributing factors, including misunderstandings about how serious flu can be.