On Feb. 3, 2021, an experimental single-dose, intranasal influenza vaccine, was safe and produced a durable immune response when tested in a Phase 1 study was published in the Journal of Clinical Investigation. The investigational vaccine, called Ad4-H5-VTN, is a recombinant, replicating adenovirus vaccine designed to spur antibodies to hemagglutinin, a protein found on the surface of influenza viruses that attaches to human cells. The investigational vaccine was developed by Emergent Biosolutions.