Also known as: neomycin sulfate, aminoglycoside antibiotic
Neomycin
Sourced from FDA-approved package inserts (DailyMed). Last verified: 2026-07-07.
What It Is & Why It's in Vaccines
Neomycin is an aminoglycoside antibiotic used in the manufacturing process of some viral vaccines (MMR, varicella, IPV, and some combination vaccines) to prevent bacterial contamination during cell culture. Most neomycin is removed during purification; trace amounts may remain.
Not deliberately added — trace residual from antibiotic use during cell culture to prevent bacterial overgrowth that would compromise the viral antigen production. Neomycin is the most common antibiotic residue in viral vaccines because it is effective against a broad range of bacteria at low concentrations and is well-tolerated in tissue culture.
Dose-in-Context
Per-Dose Quantity
≤25 mcg per dose (residual). For comparison, a typical topical neomycin preparation (e.g., Neosporin) delivers milligrams per application — orders of magnitude more.
Reference Comparison
Neomycin is a known contact sensitizer with topical use (allergic contact dermatitis rate ~1–6% with repeated topical application). The trace injectable quantities in vaccines are several orders of magnitude below topical sensitizing doses. Systemic neomycin at therapeutic doses (gram quantities IV/IM for serious infections) carries risks of nephrotoxicity and ototoxicity that are dose-dependent and not relevant to nanogram-to-microgram residual levels.
Source: DailyMed package inserts: M-M-R II, Varivax, IPOL.
Route-of-Administration Note
Injected (intramuscular/subcutaneous). Neomycin is poorly absorbed orally; injected trace quantities are rapidly cleared renally. The systemic safety considerations for gram-level parenteral neomycin do not apply to nanogram-to-microgram vaccine residuals.
Documented Adverse Effects
Allergic contact dermatitis to topical neomycin is well-established (Type IV delayed hypersensitivity). The labeled contraindication for neomycin-containing vaccines is a history of anaphylactic (immediate, IgE-mediated) reaction to neomycin — this is extremely rare. Contact dermatitis to topical neomycin is specifically NOT a contraindication to neomycin-containing vaccines (the reaction is Type IV, localized to skin, and the injected trace quantity is insufficient to trigger it).
Vaccines Containing Neomycin
MMR — M-M-R II (Merck Sharp & Dohme LLC)
Live attenuated; no adjuvant. Product contains no preservative.
MMR — PRIORIX (GlaxoSmithKline Biologicals)
Contains no gelatin — relevant for gelatin allergy. Residual ovalbumin possible from chick-embryo manufacture.
Polio (IPV) — IPOL (Sanofi Pasteur)
Inactivated whole-virus; no aluminum adjuvant.
Varicella — Varivax (Merck Sharp & Dohme LLC)
Hepatitis A — Vaqta (Merck Sharp & Dohme LLC)
Hepatitis A — Havrix (GlaxoSmithKline Biologicals)
Rabies — Imovax Rabies (Sanofi Pasteur)
ⓘ Methodology Disclaimer: Ingredient lists are sourced from official FDA-approved package inserts for the specific branded products named on each vaccine page. Formulations can change between manufacturing lots and over time — always verify against the current package insert before making a clinical decision. The presence of a substance in a vaccine does not by itself indicate harm; toxicology is dose-, route-, and context-dependent. Comparisons to reference exposure levels are provided with their sources where available, and are approximate — see the cited source for full methodology.