• Adverse event or SAE information (solicited in-clinic and via memory aids, concomitant medications, and periodic targeted physical assessments). [ Time Frame: Adverse events will be collected through 28 days following the second dose of vaccine (approximately Day 56). Serious adverse events will be collected throughout the study through Day 208. ] [ Designated as safety issue: Yes ]
  
• Proportion of subjects in each group achieving a serum neutralizing antibody titer ratio of 1:40 against the influenza A/H5N1 virus 28 days following second dose of vaccine. [ Time Frame: Approximately Day 56. ] [ Designated as safety issue: No ]
  
• Proportion of subjects in each dose group achieving a serum hemagglutination (HAI) antibody titer of 1:40 against the influenza A/H5N1 virus 28 days after receipt of the second dose of vaccine. [ Time Frame: Approximately Day 56. ] [ Designated as safety issue: No ]
  
• Geometric mean titer (GMT) and frequency of 4-fold or greater increases in neutralizing antibody titers in each group 28 days after receipt of the second dose of vaccine. [ Time Frame: Approximately Day 56. ] [ Designated as safety issue: No ]
  
• Geometric mean titer and frequency of 4-fold or greater increases in serum hemagglutination inhibition (HAI) antibody titers in each group 28 days after receipt of the second dose of vaccine. [ Time Frame: Approximately Day 56. ] [ Designated as safety issue: No ]
  

• Development of serum antibody responses against antigenically drifted variants of H5N1influenza virus. [ Time Frame: Blood samples for serum assays will be collected at Day 0 and at Days 28, 56, and 208 after the first immunization. ] [ Designated as safety issue: No ]
  
• Geometric mean titer and the frequency of 4-fold or greater increases in serum HAI antibody titers 1 month after receipt of each dose, and 7 months after receipt of the first dose of vaccine. [ Time Frame: Blood samples for serum assays will be collected at Day 0 and at Days 28, 56, and 208 after the first immunization. ] [ Designated as safety issue: No ]
  
• Geometric mean titer and the frequency of 4-fold or greater increases in neutralizing antibody titers in each group 1 month after receipt of each dose, and 7 months after receipt of the first dose of vaccine. [ Time Frame: Blood samples for serum assays will be collected at Day 0 and at Days 28, 56, and 208 after the first immunization. ] [ Designated as safety issue: No ]
  

The emergence of novel influenza A virus strains in humans (including subtype A/H5N1, H7N7 H9N2 viruses) has added urgency to ongoing efforts to develop plans for responding to potential pandemic situations. This study compares the safety, reactogenicity, and immunogenicity of increasing doses of monovalent subvirion influenza A/H5N1 virus vaccine administered by intramuscular (IM) injection to healthy adults alone or combined with the adjuvants aluminum hydroxide or MF59. The primary objectives are to determine: the dose-related safety of subvirion inactivated H5N1vaccine with and without adjuvants in healthy adults; the dose-related immunogenicity of subvirion inactivated H5N1vaccine with and without adjuvants in healthy adults approximately 1 month following receipt of 2 vaccine doses; to provide information for the selection of the best dosage level for further studies. The secondary objectives are to evaluate dose-related immunogenicity and the percent of subjects responding about 1 and 7 months after the first vaccination. The primary endpoints are: adverse event (AE) or serious adverse event (SAE) information; proportion of subjects in each dose group achieving a serum neutralizing antibody titer of 1:40 against the influenza A/H5N1 virus 28 days after receipt of the second dose of vaccine; proportion of subjects in each dose group achieving a serum hemagglutination (HAI) antibody titer of 1:40 against the influenza A/H5N1 virus 28 days after receipt of the second dose of vaccine; geometric mean titer (GMT) and frequency of 4-fold or greater increases in neutralizing antibody titers in each group 28 days after receipt of the second dose of vaccine; geometric mean titer and frequency of 4-fold or greater increases in serum HAI antibody titers in each group 28 days after receipt of the second dose of vaccine. The secondary endpoints are: GMT and frequency of 4-fold or greater increases in neutralizing antibody titers in each group 1 month and 7 months after receipt of the first dose of vaccine; geometric mean titer and frequency of 4-fold or greater increases in serum HAI antibody titers in each group 1 month and 7 months after receipt of the first dose of vaccine; development of serum antibody responses against antigenically drifted variants of H5N1 influenza virus. The primary outcome measures will be the frequencies and severities of AEs in each group and the proportions of subjects who achieve a serum neutralizing antibody titer of 1:40 against the influenza A/H5N1 virus on Day 56. About 390 healthy adults, 18 to 64 years old, inclusive, will be enrolled into this multicenter, randomized, placebo-controlled, dose-ranging clinical trial. Nine groups of randomized subjects will receive two doses of saline placebo or influenza A/H5N1 vaccine at 45, 30, or 15 micrograms; or influenza A/H5N1 vaccine at 15 or 7.5 micrograms with MF59; or influenza A/H5N1 vaccine with aluminum hydroxide at 30, 15, or 7.5 micrograms (N=30, 60 or 90/vaccine dose group total 390). Laboratory safety profile blood will be drawn prior to the first immunization. Subjects will receive 2 doses approximately 28 days apart. Subjects will be observed after inoculation and maintain a memory aid for 7 days afterwards. Subjects will be telephoned 1 to 3 days after vaccination for AE assessment, and they will return to the clinic on Day 7 for AE and concomitant medication assessment, targeted physical examination, safety laboratory tests and a review of the memory aid. Telephone calls assessing AEs will be performed after each vaccination. Serum for safety laboratory tests will be obtained prior to and approximately 7 days after first and second immunizations. Immunogenicity serum will be obtained prior to immunization, approximately 1 month after first immunization and approximately 1 month and 6 months after second immunization. This study is linked to DMID protocols 06-0005, 05-0144, 05-0145, and 07-0022.