• In multidose injectable drug delivery systems, it prevents serious adverse effects such as the Staphylococcus infection that, in one 1928 incident, killed 12 of 21 children inoculated with a diphtheria vaccine that lacked a preservative.[3] Unlike other vaccine preservatives used at the time, thiomersal does not reduce the potency of the vaccines that it protects.[4] Thiomersal is not needed in mo