A group of researchers from the University of Rochester Medical Center found that the effectiveness of US influenza vaccines during the 2010-2011 season was moderate, even if all 3 vaccine strains were well matched to circulating strains.
The authors of the work, published on Clinical Infectious Diseases, performed a case-control study on around 5000 patients with flu-like illness during the 2010–2011 flu season. The estimated efficacy of either inactivated or live-attenuated vaccine ranged from 69% in children aged 6 months-8 years to 38% in adults older than 65 years.
These results contrast those studies of poorly matched vaccines (estimated efficacy lower than 30%) but are nevertheless modest. Most of all, data regarding efficacy in older adults are concerning, although the low number of patients in this age group might have influenced this finding.