In June 2000, a joint statement on thimerosal* in vaccines was prepared by the American Academy of Family Physicians (AAFP), the American Academy of Pediatrics (AAP), the Advisory Committee on Immunization Practices (ACIP), and the Public Health Service (PHS) in response to 1) the progress in achieving the national goal declared in July 1999 to remove thimerosal from vaccines in the recommended childhood vaccination schedule, and 2) results of recent studies that examined potential associations between exposure to mercury in thimerosal-containing vaccines and health effects. In this statement, AAFP, AAP, ACIP, and PHS recommend continuation of the current policy of moving rapidly to vaccines that are free of thimerosal as a preservative. Until adequate supplies are available, use of  vaccines that contain thimerosal as a preservative is acceptable. 

A joint statement issued by AAP and PHS in July 1999 and agreed to by the AAFP later in 1999 established the goal of removing thimerosal as soon as possible from vaccines routinely recommended for infants. The goal was established as a precautionary measure. No evidence existed of any harm caused by low levels of thimerosal in vaccines. Public concern had been expressed about the health effects of mercury exposure of any sort, and the elimination of mercury from vaccines was considered a feasible means of  reducing an infant's total exposure to mercury in a world where other environmental sources of exposure are more difficult or impossible to eliminate (e.g., certain foods). 

Since July 1999, substantial progress has been made in removing thimerosal from vaccines. As of March 2000, all U.S. children had access to hepatitis B vaccines that do not contain thimerosal as a preservative. Beginning July 2000, only single-dose thimerosal-free Haemophilus influenzae type b vaccine will be produced in the United States; previously manufactured multidose vials containing thimerosal still may be in distribution. One diphtheria and tetanus toxoids and acellular pertussis vaccine (DTaP) that does not contain thimerosal is available, and it is projected that additional DTaP vaccines without thimerosal as a preservative will become available in early 2001. On the basis of this progress, the most likely maximum amount of ethylmercury that an infant may be exposed to from the routine vaccination schedule has been reduced by 60%, from 187.5 µg to 75 µg.  Measles-mumps-rubella, varicella, inactivated polio, and pneumococcal conjugate vaccines have never contained thimerosal. 

Research on the potential health effects of exposure to thimerosal is continuing, and findings will be monitored closely by PHS to determine whether any changes in policy are needed. AAFP, AAP, and PHS, in consultation with the ACIP, reaffirm the goal set in July 1999 to remove or greatly reduce thimerosal from vaccines as soon as possible. On the basis of information from the Food and Drug Administration and manufacturers, PHS projects that the United States will complete its transition to a secure routine pediatric vaccine supply free of thimerosal as a preservative by the first quarter of 2001. 

The vaccination of children in much of the world will continue to require the use of multidose vials because of cost, production, and storage capacity.  Multidose vials require a preservative to prevent microbial contamination after the vial is opened. For multidose vials, manufacturers are encouraged to seek alternatives to thimerosal.  

*Thimerosal is a derivative of ethylmercury and has been used as an additive to biologics and vaccines since the 1930s because it is effective in killing bacteria and in preventing bacterial contamination, articularly in opened multidose containers.