Monitoring veterinary vaccines for contaminating viruses.

The detection of extraneous agents (EA) has always been critical for assessing the safety associated with vaccines. Vaccines and other biological medicines are derived from living substrates. This poses particular problems with regard to assuring their efficacy and safety due to the inherent variability of starting materials, the production processes, and the complex nature of the products themselves. For viral vaccines and other biological medicines, the key to effective quality control is rigorous testing and validation applied to the seed lots and also to the final batches. The quality assurance requirements for marketing products in Europe are given in the European Pharmacopoeia (EP). With the advent of molecular biotechnology, there are increasing uses of molecular methods for the characterization and quality control of vaccines. PCR for extraneous agent testing for live and inactivated poultry vaccines has been recognized to be a valid alternative testing method and is now being used extensively as a diagnostic tool in assuring the freedom from EAs. A number of generic PCR assays for product testing have been developed and validated. The current status and issues of the application of nucleic acid testing (NAT) to the standardization and control of vaccines will be reviewed.