Porcine circoviruses (PCVs) are small (17 nm) non-enveloped viruses with a covalently closed, circular, single-stranded DNA genome. PCV type 1 (PCV-1) and PCV type 2 (PCV-2) belong to the circovirus genus within the Circoviridae family. PCV-1 was originally isolated as a contaminant of porcine kidney (PK15) cells, and although it was found to be widely distributed in domestic swine in both North America and Europe, no correlation to any porcine disease or disorder has been established. PCV-2, however, has been found to be associated with several disease syndromes in pigs. For manufacturers of biologics utilizing porcine tissue or porcine tissue-derived materials, PCVs represent a contamination risk. In fact, an independent academic laboratory detected PCV-1 in a live attenuated rotavirus vaccine using metagenomic analysis and a PCV-1-specific polymerase chain reaction (PCR). While this study did not detect PCV-1 or PCV-2 nucleic acid in rotavirus vaccine from a second manufacturer, subsequent testing by the manufacturer revealed low levels of both PCV-1 and PCV-2 DNA. The source of the PCV nucleic acid contaminating both vaccines was determined to be porcine pancreas-derived trypsin used in the manufacture of the vaccines. The manufacturer of the rotavirus vaccine that was initially found to contain PCV sequences determined that their cell banks and virus seeds were contaminated with the viral sequences. The strong safety record of both vaccines and the benefits of vaccination against rotavirus convinced both the United States Food and Drug Administration (US FDA) and the European Medicines Agency (EMA) to permit their continued use…