The committee also recommended in its prior report that the appropriate professional societies and government agencies review their policies on the non-vaccine biological and pharmaceutical products that contain thimerosal and are used in infants, children, and pregnant women. The committee’s recommendation reflected concern about total mercury burden and potential risk of certain NDDs. The committee believes that these ongoing reviews are important and should continue. At the same time, the committee recognizes that many other countries, particularly developing countries, must rely on multidose vaccine vials that use thimerosal as a preservative. Because thimerosal is an antibacterial agent that has been highly successful in preventing field contamination, its removal from multidose vials would increase the risk of bacterial infection leading to toxic shock syndrome or death. The option of using single dose vaccines, which do not require thimerosal, is not feasible for some countries because of limits in the production of single-dose vaccines and lack of infrastructure for the transportation and storage of single-dose vials in a cold-chain system. While the United States chose to eliminate thimerosal from routine childhood vaccines as a precautionary measure and because it was feasible, the committee recognizes that other countries have different constraints and other factors; their own assessments of the risks and benefits may lead those countries to reach different conclusions regarding the thimerosal content of their vaccines. Given the lack of direct evidence for a biological mechanism and the fact that all well-designed epidemiological studies provide evidence of no association between thimerosal and autism, the committee recommends that cost-benefit assessments regarding the use of thimerosal-containing versus thimerosal-free vaccines and other biological or pharmaceutical products, whether in the United States or other countries, should not include autism as a potential risk.

The committee reaffirms its previous recommendation to use standard and accepted case definitions and assessment protocols for ASD to enhance the precision and comparability of results from surveillance, epidemiological studies, and biological investigations. Studies should also address the heterogeneity in the etiology of ASD and the spectrum of clinical presentation.

The committee reaffirms its previous recommendation to conduct clinical and epidemiological studies of sufficient rigor to identify risk factors and biological markers of ASD in order to better understand genetic or environmental causes of ASD.