Which vaccines contain trace amounts of thiomersal?

Vaccines Containing Trace Amounts of Thiomersal

Since mid-2001, vaccines routinely recommended for children have been manufactured without thiomersal as a preservative and contain either no thiomersal or only trace amounts (<1 mcg mercury/dose). 1

Current Status of Thiomersal in Vaccines

Vaccines with Trace Amounts of Thiomersal

• Single-dose presentations of influenza vaccines often contain trace amounts of thiomersal (<1 mcg mercury/0.5 mL dose) 2
• Some formulations of influenza vaccine are available in reduced thimerosal-content versions 1
• Since 2001, most childhood vaccines have been reformulated to be either thiomersal-free or contain only trace amounts 1

Vaccines with Standard Amounts of Thiomersal

• Multi-dose vials of certain vaccines still contain thiomersal as a preservative (approximately 25 mcg mercury/0.5 mL dose) 1, 2
• Specific vaccines that may contain standard amounts of thiomersal include:
  • Td (Tetanus and diphtheria toxoids) 1
  • DT (Diphtheria and tetanus toxoids) 1
  • Multi-dose influenza vaccines 1, 3
  • One of two adult hepatitis B vaccines 1

Vaccines Never Containing Thiomersal

• Live attenuated vaccines have never contained thiomersal 1, 2
• This includes vaccines such as MMR (measles, mumps, rubella), varicella, and live attenuated influenza vaccine

Clinical Implications

Safety Considerations

• No scientific evidence indicates that thiomersal in vaccines causes harm 2, 4
• The elimination of mercury from vaccines has been primarily a precautionary measure 1
• Blood mercury levels in infants receiving thiomersal-containing vaccines remain below safety thresholds 5
• Ethylmercury from thiomersal is eliminated rapidly from the body with an estimated blood half-life of 7 days 5

Allergic Reactions

• Hypersensitivity to thiomersal usually consists of local delayed-type hypersensitivity reactions 1
• A localized or delayed-type hypersensitivity reaction to thiomersal is not a contraindication to receipt of a vaccine that contains thiomersal 1
• Despite theoretical concerns, there is limited scientific basis for the assertion that thiomersal-containing vaccines lead to induction of allergy 1, 4

Practical Guidance for Clinicians

When to Consider Thiomersal Content

• For patients with history of severe allergic reactions to thiomersal (rare)
• When vaccinating infants and pregnant women, single-dose thiomersal-free formulations are generally preferred when available 2
• Package inserts should be consulted for information about specific vaccine formulations 1, 3

Risk-Benefit Assessment

• The benefit of influenza vaccine with reduced or standard thiomersal content outweighs the theoretical risk from thiomersal 1
• Delaying vaccination to wait for thiomersal-free formulations could leave patients vulnerable to preventable diseases 2, 6

Common Pitfalls

• Confusing thiomersal allergy (usually delayed-type hypersensitivity) with contraindications to vaccination
• Overestimating the risks of trace thiomersal exposure compared to the risks of remaining unvaccinated
• Failing to distinguish between multi-dose vials (which contain preservative levels of thiomersal) and single-dose presentations (which contain trace or no thiomersal)
• Not recognizing that the mercury in thiomersal (ethylmercury) is eliminated more rapidly than methylmercury from environmental sources 5