Avian influenza viruses, including H1N1 and H5N1, are capable of causing an influenza pandemic. The 2009 H1N1 pandemic caused approximately 10,000 deaths in the United States, and H1N1 and H5N1 influenza outbreaks have been observed in countries around the world. Previous studies have shown that people who received an H5N1 vaccine and then received another H5N1 vaccine years later had a greater antibody response than people who only received a single vaccination. This study will evaluate the safety and immune response to an inactivated H5N1 vaccine in healthy adults who have previously received two doses of the H5N1 VN 04 ca vaccine or the H5N1 HK 03 ca vaccine or who have previously received two doses of the H7N3 ca vaccine, which is another avian influenza vaccine. The study will also enroll people who have not previously received any LAIV.~Participants who previously received an H5N1 or H7N3 vaccine will receive one injection of the H5N1 vaccine at baseline. Participants who have not received any previous LAIV will be randomly assigned to receive either one dose or two doses of the H5N1 vaccine. At a baseline study visit, participants will undergo a medical history review, physical examination, blood collection, vital sign measurements, and a pregnancy test for females. All participants will then receive one injection of the vaccine in the upper arm. After receiving the vaccine, participants will remain in the clinic for 30 minutes for observation and monitoring. All participants will attend additional study visits at Days 3 and 7. Participants who are assigned to receive one vaccination will also attend study visits at Days 28, 56, and 180. Participants who are assigned to receive two vaccinations will attend study visits at Days 28 (at which time they will receive the second vaccination), 35, 56, 84, and 208. Select baseline study procedures will occur at the follow-up study visits.
H5N1 is an influenza virus that has the potential to cause an influenza pandemic. This study will evaluate the safety and immune response to an H5N1 influenza vaccine in people who have previously received one of two versions of an H5N1 vaccine or have previously received an H7N3 vaccine and in people who have not previously received any live attenuated influenza vaccine (LAIV).