Safety and Immunogenicity of BPL-1357, A BPL-Inactivated, Whole-Virus, Universal Influenza Vaccine

Background: Influenza (flu) is a virus that infects people of all ages. Some people may have mild flu symptoms. Others may get very sick and even die from the flu. Flu vaccines help protect people against the flu, but if the flu strains in the vaccine are not a good match with the strains circulating in the community, the vaccine is not as effective. Researchers want to make flu vaccines that protect against changing flu strains. Objective: To test if a new flu vaccine is safe and if it creates an immune response. Eligibility: Healthy adults ages 18-55 who do not smoke and have not received a flu vaccine in the 8 weeks prior or a COVID-19 vaccine in the 4 weeks prior to enrollment. Design: Participants will be screened on a separate protocol. Participants will have 9 visits over 7 months. They will get a combination of study vaccine and/or placebo, both as a shot in the arm and as a spray into the nose, at 2 visits. For 7 days after getting the vaccines, they will take their temperature and complete online surveys at home to record any symptoms. At each visit, participants will have a physical exam and medical history. They will give blood and urine samples. They will have nasal testing. For this, a thin absorptive strip will be inserted into their nostril for 1 minute to collect mucus. At some visits, the inside of their nose will be wiped with a small brush to collect cells. For this, their nostril will be numbed to make it more comfortable. Some blood and nasal samples will be used for genetic testing. Participants who get flu-like symptoms during the study will be asked to collect nasal samples at home and send these samples back to NIH to test if they actually have the flu.