Most immunologically-mediated neomycin hypersensitivity is T-cell mediated. The amount of neomycin in an MMR vaccine is extremely small. There is virtually no risk of an acute onset systemic IgE-mediated hypersensitivity reaction from neomycin. A small amount of intramuscular T-cell mediated activation is also typically of no clinical significance and may actually provide a slight adjuvant effect and make the vaccination more effective. I would administer the MMR vaccination, even if the individual was patch test positive to neomycin, because the benefit of the MMR vaccination would greatly outweigh any risk of a local rash.
I hope this information is of help to you and your patient.
Eric Macy, MD, MS, FAAAAI