Toxic shock syndrome (TSS) occurs while measles vaccine is contaminated or the same vial is used for more than one session on the same day or next day. Now the question arises, why only measles vaccine causes TSS more commonly and not the other commonly used vaccines? : - It is due to the absence of preservatives. Preservatives are substances used in vaccines to prevent bacterial & fungal contamination. Measles vaccine contains limited or no amount of preservative, therefore rapid multiplication of pathogen takes place. Most of the other commonly used vaccines contain preservatives. Note : TSS can be caused by all vaccines (Park 20th/e 107), but it is mostly associated with measles vaccine.