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Early data from the Centers for Disease Control and Prevention (CDC) suggests that the 2024-2025 flu shots have significantly reduced hospitalizations due to seasonal influenza, with particularly strong results for children and teens. According to data from two healthcare networks the CDC monitors, the flu shots were at least 63% effective at preventing hospitalizations for kids and teens, with some regions showing effectiveness as high as 78%.
For adults, the effectiveness against hospitalization ranged from 41% to 55%. This data was shared in the CDC’s Morbidity and Mortality Weekly Report (MMWR) on February 28 and offers an early snapshot of flu vaccine performance for this season. The report also highlights the shots’ effectiveness in reducing outpatient visits, which include regular doctor visits, urgent care, and emergency department visits.
Vaccine Effectiveness and Impact on Flu Hospitalizations
Vaccine effectiveness (VE) reflects how well the vaccine prevents a specific health outcome—in this case, hospitalization due to the flu. When comparing vaccinated individuals to unvaccinated ones, the data indicates that kids and teens who received the flu shot had a 63% to 78% lower chance of being hospitalized for the flu. For adults, the vaccine showed a more modest but still significant reduction in hospitalizations.
Additionally, the flu shots helped reduce outpatient visits for flu-related symptoms. For children and teens, VE against outpatient visits ranged from 32% to 60%, depending on the healthcare network. For adults, effectiveness ranged from 36% to 54%. Although some groups, particularly children, may have experienced less protection against outpatient visits this year, overall, the flu shots have proven to be an effective measure in reducing severe flu complications.
Flu Vaccine Effectiveness Compared to Previous Seasons
This year’s flu shots appear to be more effective than last season’s vaccines, particularly in protecting children from hospitalizations. However, pediatric outpatient visits have not been as well protected this year, possibly due to the prevalence of the H3N2 flu subtype, which may be less well-matched to the vaccine. For adults, the flu shots are providing slightly better protection this season compared to last year’s vaccine, offering a boost in both hospitalizations and outpatient visits.
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The CDC has emphasized that these findings reinforce the importance of vaccination, particularly to avoid severe complications associated with the flu. “Vaccination with the 2024-2025 influenza vaccine reduced the likelihood of medically attended influenza and supports the CDC’s recommendation that all individuals aged six months and older receive the flu vaccine,” the MMWR report states.
H3N2 Subtype May Affect Vaccine Effectiveness for Outpatient Visits
The MMWR report proposes that the flu subtype H3N2 may explain why the vaccine has shown lower effectiveness against outpatient visits for children this year. Data from the CDC indicates that the majority of flu cases this season have been caused by influenza A viruses, with H1N1 and H3N2 subtypes being the primary contributors. The ratio of H1N1 to H3N2 viruses varies by region, which may explain the differences in vaccine performance across different healthcare networks.
Lab studies conducted with ferrets have suggested that the flu shots are a less perfect match for the circulating H3N2 viruses than for H1N1 viruses, which may be a factor in the reduced protection for outpatient visits, especially in areas where H3N2 predominates.
Looking Ahead: The Impact of Flu Vaccine Production Delays
While the 2024-2025 flu shots are showing solid protection, the fate of the next round of flu vaccines for the 2025-2026 season is uncertain. Traditionally, an advisory panel to the U.S. Food and Drug Administration (FDA) meets in early spring to select the strains for the upcoming season’s flu shots. However, the meeting scheduled for March 13 has been canceled, raising concerns about potential delays in the flu vaccine production cycle.
The cancellation could affect the timely production and availability of flu shots for the 2025-2026 season. Flu vaccine production involves growing viruses in chicken eggs, a process that requires several months of lead time. Delays in strain selection could lead to shortages of vaccines, potentially increasing the risk of serious flu illnesses and deaths in the coming year.
Despite these concerns, the CDC and FDA have been actively participating in World Health Organization (WHO)-led meetings to discuss flu vaccine strain selection. While the delay in the FDA advisory panel meeting could disrupt the U.S. strain selection process, it remains to be seen whether the agency will proceed with its own decision-making process or if the meeting will be rescheduled.
