A case of mistaken identity? Vaccinia virus in a live camelpox vaccine

Live-attenuated (LA), and inactivated adjuvant (IA) camelpox virus (CMLV) vaccines are produced in several countries worldwide. A tissue culture attenuated CMLV isolated (Jouf-78) is used to produce an LA vaccine in Saudi Arabia (Hafez et al., 1992). DNA extracts from the Saudi LA vaccine were used as positive controls for a routine ATIP PCR produced fragments longer than 881 bp. PCR-amplified ATIP sequences were similar to vaccinia virus (VACV) Lister strain. PCR and sequence analysis of two extracellular enveloped virus (EEV)-specific (A33R and B5R), and two intracellular mature virus (IMV) (L1R and A27L) othrologue genes from the vaccine DNA extracts confirmed the finding. CMLV sequences were not detected in vaccine DNA extracts. A VACV Lister strain imported from Switzerland was used in control experiments during initial testing of the Saudi LA vaccine. High antigenic similarity between VACV and CMLV, and a possible contamination event during production may have caused this issue. Environmental and health impact studies were recommended because early VACV vaccines produced in some European countries contained nonhighly attenuated strains that were not adequately screened for adventitious agents.