 [ Symptoms ] i know studies show flu vaccines preserved with thimerosal are safe but is there an alternative [ Disease ] tiny doses of a mercury compound called thimerosal keep multidose vials of flu vaccine safe from contamination with bacteria before thimerosal was added to multidose vials contamination caused serious adverse events exhaustive studies fail to find any reason to believe that thimerosal is unsafe but if you do not want thimerosal you do not have to have it single dose syringes of flu vaccine do not need thimerosal and do not have any neither does the flumist nasal spray vaccine if you prefer a thimerosal free vaccine check with your provider to see if one is available if not check with your state or local health department to see where you can find one