This randomized, double-blind, placebo-controlled study investigated the efficacy, safety, and immunogenicity of LAIV in community-dwelling ambulatory adults ≥60 years of age in South Africa in 2001. Nose and throat swabs were obtained for influenza virus culture based on the symptoms of influenza-like illness. A total of 3242 subjects were enrolled, with a mean age of 69.5 years. The efficacy of LAIV against influenza viruses antigenically similar to the vaccine was 42.3% (95% CI, 21.6-57.8%). Efficacy against A/H3N2 viruses was 52.5% (95% CI, 32.1-67.2%); vaccine efficacy was not observed against antigenically similar B strains. In post hoc analyses, efficacy in subjects 60 to <70 years of age was 41.8% and -22.7% against A/H3N2 and B, respectively and 65.7% and 9.9%, respectively, for subjects ≥70 years. Reactogenicity events were higher among LAIV than placebo recipients during 11 days postvaccination (P = 0.042), including runny nose/nasal congestion, cough, sore throat, headache, muscle aches, tiredness, and decreased appetite. Rates of serious adverse events were similar for LAIV and placebo recipients. This was the first demonstration of statistically significant protection by LAIV against culture-confirmed influenza in adults ≥60 years of age. These results suggest that LAIV may provide an additional public health tool in the prevention of influenza in the elderly. (ClinicalTrials.gov identifier, NCT00217230.).
- Live attenuated influenza vaccine