Flu Vaccination Linked to Fewer Severe Outcomes in Older Adults, Fewer ED Visits in Children

Two studies presented at IDWeek 2026 in Washington, DC, add real-world evidence for seasonal influenza vaccination in both older adults and children.^1,2 A retrospective cohort study from Geisinger Health System associated vaccination with fewer ICU admissions among older adults who came to the emergency department (ED) with influenza.¹ A separate analysis from the CDC’s VISION Network estimated that 2025-2026 seasonal influenza vaccines reduced the risk of influenza-associated ED and urgent care (UC) encounters among children and adolescents by 36%.²

Influenza Vaccination in Older Adults

Older adults bear a disproportionate burden of severe influenza, and annual vaccination remains central to prevention.^1,3 However, real-world evidence on vaccination and illness severity among ED patients is limited, according to investigators led by presenting author Manouj Kumar, MD. Geisinger serves a mostly rural, older population with substantial comorbidity, which the investigators described as a relevant setting for studying these outcomes.¹

The retrospective cohort study included adults aged 65 or older who came to Geisinger EDs with RT-PCR-confirmed influenza between October 1, 2024, and April 30, 2025. Individuals were counted as vaccinated if they had received a seasonal vaccine at least 14 days before presentation, as documented in the electronic health record or immunization registry.¹

Lower ICU Admission Rates Among Vaccinated Patients

Of 452 patients, 80 (17.7%) were vaccinated. The 2 groups had similar baseline characteristics. Median age was 80 years in vaccinated patients and 78 years in unvaccinated patients. Chronic obstructive pulmonary disease was present in 41.3% and 33.9%, respectively.¹

ICU admission occurred in 2.5% (2/80) of vaccinated patients compared with 10.5% (39/372) of unvaccinated patients. That is an 8.0-percentage-point absolute difference (P = .029). Vaccinated patients also had shorter stays, although neither difference was significant on two-sided testing:¹

The mean hospital stay was 4.43 days versus 5.20 days (P = .091). Among the 41 ICU patients, the mean ICU stay was 0.67 days versus 3.24 days (P = .065).

Several outcomes did not differ significantly between groups:¹

• Hospital admission: 95.0% vs 96.2%;
• Oxygen use: 75.0% in both groups;
• Antibiotic prescribing: 47.5% vs 45.2%; and
• Antiviral prescribing: 90.0% vs 87.4%.

The investigators noted that only 17.7% of the cohort had documented vaccination. They said rural access and insurance-related barriers warrant further study. The analyses were unadjusted. Planned next steps include propensity score matching, analyses across multiple seasons, and evaluation of targeted electronic health record vaccination reminders.¹

Pediatric Vaccine Effectiveness in the 2025-2026 Season

During the 2025-2026 US influenza season, drifted influenza A (H3N2) subclade K viruses predominated, and influenza activity among children was high. To estimate vaccine effectiveness (VE) in this season, investigators led by Katherine Adams, DrPH, MPH, of the CDC’s National Center for Immunization and Respiratory Diseases, used a test-negative design. The study included children and adolescents aged 6 months to 17 years with ED or UC encounters for acute respiratory illness and molecular influenza testing at 6 VISION sites between October 1, 2025, and April 30, 2026. Models were adjusted for age, sex, race and ethnicity, calendar day, and site.²

Of 76,815 encounters, 25,496 were influenza cases and 51,319 were controls. Of the cases, 22% were vaccinated, compared with 29% of controls. Key adjusted VE estimates were as follows:²

• Overall: 36% (95% CI, 33%-39%);
• Influenza A: 38% (95% CI, 35%-41%);
• Influenza B: 31% (95% CI, 27%-36%);
• Aged 6 months to 4 years: 47% (95% CI, 42%-51%);
• Aged 5 to 17 years: 29% (95% CI, 25%-33%);
• ED encounters: 41% (95% CI, 38%-45%); and
• UC encounters: 28% (95% CI, 24%-33%).

VE was 40% at 14 to 59 days after vaccination, 37% at 60 to 119 days, and 34% at 120 days or more.²

Moderate Effectiveness, Meaningful Impact

The VISION investigators concluded that even moderate VE can substantially reduce the influenza burden among children and adolescents. The highest protection was seen in children aged younger than 5. The Geisinger investigators said continued vaccination outreach and adjusted analyses will help translate their findings into clinical practice.¹

The VISION authors noted that their findings do not necessarily represent the official position of the CDC.²

REFERENCES

1. Kumar M, Tice AM, Law JM, Kwon T, Wolk DM. Effectiveness of seasonal influenza vaccination in reducing severe outcomes among older adults presenting to the emergency department: a retrospective cohort study. Poster presented at: IDWeek 2026; October 21-October 24; Washington D.C. Submission ID 2416323.

2. Adams K, Reeves EL, Weber ZA, et al. Effectiveness of 2025–2026 seasonal influenza vaccines against US pediatric influenza-associated emergency department and urgent care encounters—VISION Network, October 1, 2025–April 30, 2026. Poster presented at: IDWeek 2026; October 21-October 24; Washington D.C.

3. Grohskopf LA, Ferdinands JM, Blanton LH, et al. Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices—United States, 2024–25 influenza season. MMWR Recomm Rep. 2024;73(RR-5):1-25. doi:10.15585/mmwr.rr7305a1