Transmission electron micrograph (TEM) of an experimental influenza vaccine comprising haema- gluttinin particles. The particles seen here are derived from the protein coats of many influenza viruses. These protein subunits contain antigens specific to this strain of virus, which alert the body to the presence of infection. Administered to a patient, these antigens may arouse the immune system to produce antibodies to combat any future infection by this virus. Because influenza viruses can change the structure of their haemagglutinin coat, many strains of this virus occur, & vaccines can yet only protect against one or other viral strain.Mag:x200,000 at 8x10,x28,570 at 35mm size."