The purpose of this study is to compare the safety and immunogenicity over a 9-month period of five different dosages of Ad4-H5-Vtn in volunteers (Vaccinees) who receive three doses of the study vaccine or placebo. In addition, transmission of Ad4-H5-Vtn will be evaluated in all Household Contacts residing with the vaccinated volunteers.

Vaccinees also may participate in a substudy in which they receive a booster vaccination with the licensed Influenza Virus Vaccine, H5N1 (Sanofi Pasteur).

At least 160 healthy Vaccinees will be randomized into 5 ascending dosage cohorts each consisting of at least 32 volunteers. In each dosage cohort Vaccinees will be randomly assigned to receive 3 doses of either Ad4-H5-Vtn or placebo separated by approximately 56 days. Volunteers will be followed for 168 days post-third vaccination.

Inclusion Criteria:

• Healthy adults and their healthy adult household contacts.

Exclusion Criteria:

• Healthcare workers who have direct contact with patients who are immunodeficient, are HIV-positive, have an unstable medical condition, or are under the age of 18.
• Childcare workers who have direct contact with children 5 years old and younger.
• Resides with Household Contacts who are under the age of 18 or over the age of 65.
• Received or plans to receive licensed inactivated 2009 H1N1 influenza vaccine from 14 days prior to 14 days after any study vaccination.
• Received or plans to receive any other licensed vaccines from 30 days prior to the first study vaccination until 30 days after the third study vaccination.