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 elderly.76 The use of MF59 was further expanded to pandemic and avian influenza vaccines.77 Other adjuvants i