Has thiomersal (mercury-containing preservative) been used in any vaccines over the last decade?

Thiomersal Use in Vaccines Over the Last Decade

Yes, thiomersal (thimerosal) has continued to be used in some vaccines within the last 10 years, primarily in multi-dose vial presentations of inactivated influenza vaccines. 1

Current Status of Thiomersal in Vaccines

Thiomersal is a mercury-containing preservative that has been used in vaccines since the 1930s to prevent bacterial contamination, particularly in multi-dose vials. The current usage pattern shows:

• Multi-dose influenza vaccines: Still contain thiomersal as a preservative (25 mcg mercury/0.5-mL dose) 1
• Single-dose presentations: Most are thiomersal-free or contain only trace amounts (<1 mcg mercury/dose) 1
• Live attenuated influenza vaccines (LAIV): Do not contain thiomersal 1

Transition Away From Thiomersal

Since 1999, there has been a concerted effort to reduce or eliminate thiomersal in vaccines:

• By 2004,27 of 29 vaccine products under CDC contract did not contain thiomersal as a preservative 1
• Since mid-2001, vaccines routinely recommended for infants have been manufactured either without thiomersal or with only trace amounts 1
• The availability of thiomersal-free vaccine formulations has continued to expand, particularly for vulnerable populations like infants and pregnant women 1

Regulatory and Policy Considerations

Several factors have influenced thiomersal use in vaccines:

• As of 2006, six states had enacted legislation banning the administration of vaccines containing mercury, with varying definitions of mercury content 1
• The American Academy of Pediatrics (AAP) supports the World Health Organization recommendations for continued use of thiomersal as a preservative in multi-dose vials in the global vaccine supply 1
• The benefits of timely vaccination are considered to outweigh theoretical risks from thiomersal exposure 1

Safety Evidence

Multiple studies have examined thiomersal safety:

• No scientific evidence indicates that thiomersal in vaccines leads to serious adverse events 1
• Evidence has accumulated supporting the absence of harm from thiomersal-containing vaccines 1
• Studies have shown that mercury levels in blood, feces, and urine of children who received thiomersal-containing vaccines were much lower than regulatory thresholds 2
• Epidemiological studies have not confirmed any link between thiomersal-containing vaccines and autism spectrum disorders or other neurodevelopmental disorders 3

Clinical Implications

For healthcare providers, several practical considerations exist:

• When available and permitted by state law, single-dose, thiomersal-free formulations are generally preferred for infants and pregnant women
• In settings where multi-dose vials are the only option, the benefits of vaccination outweigh theoretical risks from thiomersal exposure 1
• In developing countries, multi-dose vials remain important for vaccine delivery, and thiomersal continues to play a crucial role in preserving vaccine safety 4

Common Pitfalls and Caveats

• Confusion with methylmercury: Thiomersal contains ethylmercury, which has different pharmacokinetics than methylmercury found in food. Ethylmercury is eliminated more rapidly from the body 2
• Delayed vaccination: Waiting for thiomersal-free vaccines when they're not readily available may leave patients vulnerable to preventable diseases 1
• Hypersensitivity reactions: While rare, delayed-hypersensitivity reactions to thiomersal can occur, though these are not considered contraindications to thiomersal-containing vaccines 2

In summary, while efforts have successfully reduced thiomersal use in many vaccine formulations over the past decade, it continues to be used as a preservative in some multi-dose vaccine presentations, particularly for influenza vaccines.