The goals of this study are to investigate the safety, reactogenicity, and immunogenicity of a single dose of monovalent subvirion influenza vaccine produced from a clade 2 A/H5N1 vaccine administered by intramuscular injection to healthy adults and the elderly who have previously received at least 2 doses of clade 1 A/H5N1 vaccine. In addition, this study will compare these results to individuals who are receiving 2 doses of the clade 2 A/H5N1 vaccine for the first time. The primary objective of the study is to compare the immune response following a single low-dose (15 mcg) to a single high-dose (90 mcg) of influenza vaccine derived from the clade 2 virus A/H5N1/Indonesia/05/05 in individuals who have previously received at least 2 doses of an influenza vaccine derived from the clade 1 virus A/H5N1/Vietnam/1203/2004 (A/VN/1203/04). The secondary objectives will: compare the immune response following a single low-dose (15 mcg) or single high-dose (90 mcg) of influenza vaccine derived from the clade 2 virus A/H5N1/Indonesia/05/05 in individuals who have previously received at least 2 doses of an influenza vaccine derived from the clade 1 virus A/H5N1/Vietnam/1203/2004 (A/VN/1203/04) to a group that has not received any previous A/H5N1 vaccine but who will receive 2 doses of an influenza vaccine derived from the clade 2 virus A/H5N1/Indonesia/05/05; evaluate the factors associated with immunologic response to a single dose of a vaccine derived from a clade 2 virus among individuals who have previously received at least 2 doses of vaccine derived from a clade 1 virus; evaluate the safety of a single dose of subvirion inactivated vaccine derived from the clade 2 virus A/H5N1/Indonesia/05/05 in individuals who have previously received at least 2 doses of an influenza vaccine derived from the clade 1 virus A/H5N1/Vietnam/1203/2004 (A/VN/1203/04); explore immunologic responses following vaccination with a clade 2 vaccine from A/H5N1/Indonesia/05/05 to influenza strains other than A/H5N1/Indonesia/05/05, including A/VN/1203/04; evaluate the immune responses of previously unvaccinated individuals after 1 or 2 doses of clade 2 virus A/H5N1/Indonesia/05/05 vaccine; and evaluate the duration of antibody responses following 1 or 2 doses of vaccine derived from the clade 2 virus A/H5N1/Indonesia/05/05. This study will recruit 600 healthy volunteers aged 19 years or older, in the United States, who have previously participated in a linked DMID-sponsored study. This study is linked to DMID protocols 04-063, 05-0090, 04-076, 05-0015, 05-0127, 05-0141, 06-0089, 04-062, 06-0052, and 08-0030. The study will be conducted at up to 7 vaccine centers. Subjects who previously received at least 2 doses of the clade 1 vaccine derived from the A/H5N1/Vietnam/1203/2004 virus will be randomized to receive a single dose of either 15 mcg or 90 mcg of a clade 2 vaccine derived from the A/H5N1/Indonesia/05/05 virus in a 1:1 ratio. H5 naïve subjects who previously received at least 2 doses of a placebo will be randomized to receive 2 doses of either the 15 mcg or 90 mcg of a clade 2 vaccine derived from the A/H5N1/Indonesia/05/05 virus in a 1:1 ratio. Volunteers will be observed in the clinic for 15 minutes after inoculation, and will maintain a memory aid to record oral temperature and systemic and local adverse events (AEs) for 8 days following each vaccination. Volunteers will be contacted by telephone 1 to 3 days after each vaccination to assess for the occurrence of AEs, and they will return to the clinic 8-10 days after each vaccination for AE and concomitant medication assessment, a targeted physical examination (if indicated), and review of the memory aid. T