Mercury in vaccines: how much is too much?

By Holly Fleming

Published on April 11, 2006

Seven states have adopted the anti-mercury bills: California, Washington, New York, Illinois, Iowa, Missouri, and Delaware. Similar bills were defeated in five other states.

The bills prohibit shots with more than trace thimerosal--a mercury-based antibacterial agent--for pregnant women and children under the age of three. Thimerosal came into use for vaccines sold in multi-dose vials. Single-dose vials don't need thimerosal, but clinics preferred multi-dose for convenience and lower price.

Thimerosal exposure rose in the 1990s when the CDC added five new shots for infants. In 1999, manufacturers began to phase thimerosal out.

In 2004, flu shots containing thimerosal were added to the childhood immunization schedule. The CDC refused to recommend thimerosal-free shots. Angered, lawmakers began pushing for bans.

States face opposition from groups such as the American Academy of Pediatrics. The Academy and its allies say there is no proof that the small amount of mercury is harmful. They argue that restrictions could undermine confidence in vaccines.

Concern was also voiced about worldwide immunization programs that use thimerosal. The World Health Organization would face cost and logistical problems without it.

Last year, pharmaceutical companies contributed about $1.54 million to the Academy. The group also received about $1.55 million from the CDC.

Comment on this article →