Quadrivalent Influenza HA Stem Vaccine VRC-FLUMOS0122-00-VP (SteMos1) With and Without ALFQ Adjuvant in Healthy Adults

Background: Influenza (flu) is a contagious respiratory illness caused by viruses. Flu symptoms can range from mild to severe, and the illness can be fatal. Vaccines help the body learn to prevent or fight infections such as flu. Some vaccines are combined with adjuvants. Adjuvants are special salts or fats that help vaccines work better. Researchers are looking for ways to make flu vaccines more effective. Objective: To test a new flu vaccine with and without a new adjuvant. Eligibility: Healthy adults aged 18 to 50. They must have had at least 1 flu vaccine since 2020. Design: Participants will have 12 clinic visits over 15 months. The vaccine is given as an injection into the muscle of the upper arm. Participants will be vaccinated during 2 visits spaced 4 months apart. Half will receive just the vaccine; half will receive the vaccine plus the adjuvant. They will be monitored for at least 30 minutes after each shot. Participants will keep a diary for 7 days after each shot. They check their temperature every day and record any symptoms. Participants will have 10 follow-up clinic visits plus 4 phone calls. They will have 4 to 10 tablespoons of blood drawn at each clinic visit. Fluid samples will be collected from their nose and mouth. They will be checked for any health changes. Participants may opt to undergo apheresis: Blood will be taken from the body through a needle inserted into a vein. The blood will pass through a machine that separates out the white blood cells. The remaining blood will be returned to the body through a different needle.