July 22, 2026

Influenza Vaccine Effectiveness Against Outpatient Acute Respiratory Illness With Laboratory-Confirmed Influenza, United States, 2024–25 Season 
Investigators enrolled outpatients aged ≥8 months with acute respiratory illness symptoms from outpatient health clinics, urgent care clinics, and emergency departments in seven states. Upper respiratory specimens were tested for influenza type/subtype by reverse-transcriptase polymerase chain reaction (RT-PCR). Influenza VE was estimated with a test-negative design comparing odds of testing positive for influenza among vaccinated versus unvaccinated participants controlling for age, study site, underlying health status, and month of illness onset. Among 6,793 enrolled patients, 2,016 (30%) tested positive for influenza including 961 A(H3N2), 770 A(H1N1)pdm09, and 183 B/Victoria. Overall vaccine effectiveness against any influenza illness was 33% (95% Confidence Interval [CI]: 24 to 41): 27% (95% CI: 14 to 39) against influenza A(H3N2), 37% (95% CI: 24 to 48) against A(H1N1)pdm09, and 40% (95% CI: 12 to 59) against B/Victoria. They did not detect statistically significant interaction between current and prior season vaccination.

Effect of High-dose versus Standard-dose Influenza Vaccines on Hospitalization Outcomes and Mortality in Older Adults: A Systematic Review and Meta-analysis 
Authors searched MEDLINE, Embase, the Cochrane Central Register of Controlled Trials (CENTRAL), Global Health, and ClinicalTrials.gov from inception to Sept 3, 2025, for randomised trials comparing HD-IIV (60 μg of haemagglutinin per strain) with SD-IIV (15 μg of haemagglutinin per strain) in adults aged 65 years or older. A total of 1,422 records were identified. After screening 813 titles and abstracts, from which 84 full texts were assessed for eligibility, 14 unique RCTs with 581,845 participants were eligible and included in the analyses.  Compared with SD-IIV, HD-IIV reduced hospitalisation for influenza (RR 0·61 [95% CI 0·50–0·74]; I2=0%; absolute risk difference −4 events per 10,000 vaccinated individuals [95% CI −5 to −3]; high certainty). There was little or no difference between the effects of HD-IIV and SD-IIV on all-cause mortality (RR 0·98 [0·92–1·05]; I2=0·0%; absolute risk difference −1 event per 10 000 vaccinated individuals [−4 to 3]; moderate certainty). HD-IIV could be considered as a strategy to reduce hospitalisation burden in adults 65 years or older; however, the evidence does not support routine preferential use across all older adults irrespective of context.