ich is in fact a nanoscale material74 that was developed in the 1920s for the tetanus and diphtheria toxoids,75 approval for a new adjuvant did not occur until 1997, with the introduction of the oil-in-water emulsion of squalene oil and polysorbate 80 and sorbitan trioleate surfactants (MF59) in the seasonal influenza vaccine for the eld