This is a phase 3, double-blind, randomized, placebo- controlled trial with two groups of participants to receive seasonal trivalent split, inactivated influenza vaccine (A/H1N1; A/H3N2 and B) or placebo (phosphate buffered saline). A total of about 480 healthy male and female adults 18 through 65 years of age; 320 participants will be randomized to receive vaccine and160 will receive placebo (a 2:1 ratio). At least 25% of the participants (N=120) will be >/= 45 years of age (80 vaccine and 40 placebo recipients).