Great progress has been made in removing thimerosal from vaccines. Manufacturers have been able to accomplish this goal through changing their manufacturing processes, including a switch from multi-dose vials, which generally require a preservative, to single-dose vials or syringes. Since 2001, all vaccines manufactured for the U.S. market and routinely recommended for children < 6 years of age have contained no thimerosal or only trace amounts (< 1 microgram of mercury per dose remaining from the manufacturing process), with the exception of inactivated influenza vaccine. In addition, all of the routinely recommended vaccines that had been previously manufactured with thimerosal as a preservative (some formulations of DTaP, Haemophilus influenzae b conjugate (Hib), and hepatitis B vaccines) had reached the end of their shelf life by January 2003. In the past, prior to the initiative to reduce or eliminate thimerosal from childhood vaccines, the maximum cumulative exposure to mercury via routine childhood vaccinations during the first six months of life was 187.5 micrograms. With the introduction of thimerosal-preservative-free formulations of DTaP, hepatitis B, and Hib, the maximum cumulative exposure from these vaccines decreased to less than three micrograms of mercury in the first 6 months of life. With the addition of influenza vaccine to the recommended vaccines, an infant could receive a thimerosal-containing influenza vaccine at 6 and 7 months of age. This would result in a maximum exposure or 28 micrograms via routine childhood vaccinations. This level is well below the EPA calculated exposure guideline for methylmercury of 65 micrograms for a child in the 5th percentile body weight during the first 6 months of life. Currently, all hepatitis vaccines manufactured for the U.S. market contain either no thimerosal or only trace amounts. Also, DT, Td, and Tetanus Toxoid vaccines are now available in formulations that contain no thimerosal or only trace amounts (see http://www.fda.gov/cber/vaccine/thimerosal.htm#t3). Furthermore, all new vaccines licensed since 1999 are free of thimerosal as a preservative. Inactivated influenza vaccine was added to the routinely recommended vaccines for children 6 to 23 months of age in 2004. FDA has approved thimerosal–preservative free formulations (containing either no or only trace amounts of thimerosal) for the inactivated influenza vaccines manufactured by Sanofi Pasteur and Chiron. These influenza vaccines continue to be marketed in both the preservative free and thimerosal-preservative containing formulations. In addition, in August 2005, FDA licensed GlaxoSmithKline's inactivated influenza vaccine, which contains 1.25 micrograms mercury per dose. Of the three licensed inactivated influenza vaccines, Sanofi Pasteur's Fluzone is the only one approved for use in children down to 6 months of age. Chiron's Fluvirin is approved for individuals 4 years of age and older, and GSK's Fluarix is approved for individuals 18 years of age and older. The live attenuated influenza vaccine (FluMist, manufactured by MedImmune), which contains no thimerosal, is approved for individuals 5 to 49 years of age. For the 2005-2006 season, Sanofi Pasteur was able to manufacture up to 8 million doses of thimerosal-preservative free influenza vaccine. Based on an estimated annual birth cohort in the United States of 4 million, there are 6 million infants and children between the ages of 6 and 23 months, most of whom would need two doses each. Thus, the amount of thimerosal-preservative-free vaccine that is available based on current manufacturing capacity is well below the number of doses needed to fully vaccinate this age group. FDA is in discussions with manufacturers of influenza vaccine regarding their capacity to further increase the supply of preservative-free formulations. | 
