FDA and the other PHS agencies believe that vaccines licensed for use in the US are safe and effective. However, because even the perception of risk could have negative consequences for the use of vaccines and because it is possible to decrease the risk of an already safe product even further, manufacturers of affected vaccines have agreed to change the source of the bovine derived material used during production of the working seeds and cell banks and for routine production (see "Recommendations for the Use of Vaccines Manufactured with Bovine Derived Materials" section of this web site for details). Also reference the question, "What is FDA doing now to assure that vaccine companies follow guidance, letters, and PTC documents on sourcing of bovine materials?" | 
