Flu activity wanes in US after record surge
Key takeaways:
- At least 43 million illnesses and 560,000 hospitalizations have been attributed to influenza this season.
- There have been 24,000 deaths attributable to influenza, including 151 pediatric deaths.
This influenza season has been particularly severe in the United States, with CDC data showing a rate of hospitalization related to flu that is higher than any other season in the past 14 years.
As of March 15, there have been at least 43 million illnesses and approximately 560,000 hospitalizations attributable to influenza, according to the CDC. The cumulative rate of 116.5 influenza hospitalizations per 100,000 people is the highest since the 2010-2011 season, the CDC said.
CDC data also show there have been 24,000 deaths attributable to influenza so far this season, including 151 pediatric deaths.
The CDC classified the season as “high severity” overall and across all age groups for the first time since 2017-2018, a recent benchmark for bad influenza seasons.
Data from the CDC’s FluView show the estimated percentage of outpatient and ED visits attributed to influenza-like illness — one measure used by CDC to track the severity of an influenza season — dropped to 3.9% as of March 15, a significant decline from a peak of 7.8%, which was the highest rate since the 2009 swine flu pandemic.
Asked what may have caused that spike in cases in January and February, a CDC spokesperson told Healio that influenza activity often increases during this time, so “it was not unusual to see an increase in flu activity during those months.”
‘Moderate impact’ on hospital capacity
According to Paul Biddinger, MD, chief preparedness and continuity officer at Massachusetts General Hospital, although there was a significant surge in influenza at his facility, the biggest challenge for hospitals “was still simply the very high demand for medical care overall and limited capacity in most of the health care system.”
“The surge in flu did have a moderate impact on hospital capacity at its peak, but it did not cause hospitals to need to postpone necessary care,” Biddinger told Healio. “Even though the flu surge is now waning, hospitals are still dealing with very high capacity and difficulties in discharging patients to a strained post-acute hospital care system.”
During the peak in cases earlier this year, Healio | Infectious Disease News Editorial Board Member William Schaffner, MD, professor of preventive medicine in the department of health policy and professor of medicine in the division of infectious diseases at Vanderbilt University Medical Center, said the severe influenza season was affecting the “entire spectrum of the population” — many of whom were unvaccinated, he said.
According to data published in MMWR last month, vaccination this season reduced influenza-related visits to a doctor by up to 54% among adults and 60% among children and adolescents. It reduced influenza-related hospitalizations by up to 55% among adults and 78% among children and adolescents.
Next season’s vaccines
The CDC recommends that everyone aged 6 months or older get vaccinated against influenza.
Next season’s influenza vaccine makeup was set by the FDA without any input from its own vaccine advisors after the agency canceled a scheduled meeting of the Vaccines and Related Biological Products Advisory Committee meeting.
That committee traditionally meets each March to discuss which viruses should be included in vaccines for the upcoming influenza season and to vote on the formulation of the vaccines. Instead, the FDA said it met with CDC and Department of Defense experts to determine the composition of the vaccines.
The recommendations align with those from WHO. They suggest the 2025-2026 influenza season trivalent formulation of egg-based influenza vaccines contain:
- an A/Victoria/4897/2022 (H1N1)pdm09-like virus;
- an A/Croatia/10136RV/2023 (H3N2)-like virus; and
- a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.
The recommendations for trivalent formulation of cell-, recombinant protein- or nucleic acid-based influenza vaccines are:
- an A/Wisconsin/67/2022 (H1N1)pdm09-like virus;
- an A/District of Columbia/27/2023 (H3N2)-like virus; and
- a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.
In a press release, the FDA said it anticipates that there will be an “adequate and diverse supply” of approved influenza vaccines next season.
“We very much need to continue to emphasize annual vaccination campaigns to limit the spread and impact of influenza each year,” Biddinger said.
References:
- CDC. FluView Interactive: National, regional, and state level outpatient illness and viral surveillance. https://gis.cdc.gov/grasp/fluview/fluportaldashboard.html. Updated March 21, 2025. Accessed March 24, 2025.
- Frutos AM, et al. Morb Mortal Wkly Rep MMWR. 2025;doi:10.15585/mmwr.mm7406ac.
- Recommendations announced for influenza vaccine composition for the 2025-2026 northern hemisphere influenza season. https://www.who.int/news/item/28-02-2025-recommendations-announced-for-influenza-vaccine-composition-for-the-2025-2026-northern-hemisphere-influenza-season. Published Feb. 28, 2025. Accessed March 23, 2025.
- Influenza vaccine composition for the 2025-2026 U.S. influenza season. https://www.fda.gov/vaccines-blood-biologics/influenza-vaccine-composition-2025-2026-us-influenza-season. Published March 13, 2025. Accessed March 24, 2025.
- CDC. Weekly US influenza surveillance report: Key updates for week 11, ending March 15, 2025. https://www.cdc.gov/fluview/surveillance/2025-week-11.html. Published March 21, 2025. Accessed March 24, 2025.
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CDC. Weekly US influenza surveillance report: Key updates for week 11, ending March 15, 2025. https://www.cdc.gov/fluview/surveillance/2025-week-11.html. Published March 21, 2025. Accessed March 24, 2025.
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