Can individuals with a mercury allergy receive a flu shot?

Mercury Allergy and Influenza Vaccination

Yes, individuals with mercury allergy can safely receive the flu shot, as delayed-type hypersensitivity to thimerosal (the mercury-containing preservative) is not a contraindication to vaccination. 1

Understanding Thimerosal and Mercury Allergy

Thimerosal hypersensitivity is typically a delayed-type (cell-mediated) reaction, not an immediate anaphylactic response. 1 This distinction is critical:

• Thimerosal elicits positive delayed-type hypersensitivity patch tests in 1-18% of persons tested, but these results have limited or no clinical relevance 1
• The majority of patients do not experience reactions to thimerosal administered in vaccines even when patch or intradermal tests indicate hypersensitivity 1
• A localized or delayed-type hypersensitivity reaction to thimerosal is explicitly not a contraindication to receiving thimerosal-containing vaccines 1

Current Vaccine Availability and Options

Multiple thimerosal-free or trace-thimerosal influenza vaccine formulations are now widely available, providing additional options for concerned patients 1:

• Many single-dose syringes and vials contain no thimerosal or only trace amounts (<1 mcg mercury/dose) 1
• Live attenuated influenza vaccine (LAIV) does not contain thimerosal 1
• Manufacturers have been delivering increasing amounts of thimerosal-free influenza vaccine annually 1

Clinical Recommendation

Do not delay or withhold influenza vaccination in patients with mercury allergy or thimerosal sensitivity. 1 The Advisory Committee on Immunization Practices (ACIP) and American Academy of Pediatrics (AAP) are clear on this point:

• The benefits of influenza vaccination outweigh any theoretical risk from thimerosal exposure 1
• No scientific evidence indicates that thimerosal in vaccines leads to serious adverse events 1
• Children should receive any available formulation rather than delaying immunization while waiting for thimerosal-free vaccine 1

Important Distinction: True Contraindications

The only hypersensitivity contraindication to influenza vaccine is anaphylactic hypersensitivity to vaccine components 1:

• Anaphylactic reactions to neomycin (present in some vaccines) are a contraindication 1
• Anaphylactic hypersensitivity to eggs or other vaccine components requires physician consultation before vaccination 1
• Contact dermatitis or delayed-type reactions do not constitute contraindications 1

Practical Approach

If a patient reports mercury allergy:

1. Clarify the type of reaction: Ask specifically about the nature of any previous mercury exposure and reaction 1
2. Distinguish delayed from immediate hypersensitivity: Contact dermatitis or positive patch tests are not contraindications 1
3. Offer thimerosal-free options if available and preferred: Many formulations exist without thimerosal 1
4. Do not withhold vaccination: Even if only thimerosal-containing vaccine is available, proceed with vaccination 1

Common Pitfall to Avoid

Do not confuse delayed-type hypersensitivity (contact dermatitis) with true anaphylactic allergy. 1 Research demonstrates that over 90% of patients with documented delayed-type hypersensitivity to thimerosal tolerate intramuscular vaccination without significant reaction 2. The clinical relevance of positive patch testing is minimal in the vaccination context 1.