Tam YH, et al. - Researchers here tested if, in tropical and subtropical areas with more prolonged influenza seasons, twice-annual influenza vaccination might provide older adults with improved immunity against influenza. Observations revealed some reductions in immune responses in the twice-annual vaccination group compared with the once-annual vaccination group, in the context of unchanging vaccine strains. During the summer and autumn, the protection was likely to have been improved for the twice-annual vaccination group due to the continued circulation of the A/Switzerland/9715293/2013(H3N2) virus.