When live, attenuated poliovirus vaccine was used in the US, its production and testing was regulated by the Food and Drug Administration. Guidelines for preparing and testing the vaccine can be found in the Code of Federal Regulations – the codification of the rules published in the Federal Register by the executive departments and agencies of the Federal Government. While reading the 1991 regulations for OPV, I came across the following curious statement:
Each seed virus used for vaccine manufacture shall be prepared from an acceptable strain in monkey kidney cell cultures, derived from animals…or in a cell culture of a type determined to be suitable by the Director…The seed virus used in vaccine manufactures shall be demonstrated to be free of extraneous microbial agents except for the unavoidable bacteriophage.
Some live human virus vaccines have been shown to contain bacterial viruses. Why would there be ‘unavoidable bacteriophage’ in seed virus and vaccines? If you know the answer, post it in the comments section, and I’ll explain fully tomorrow. I’ll also tell you why this has been an all-poliovirus week at virology blog.