Biologic and Biophysical Markers of a Live Varicella Vaccine Strain (Oka): Identification of Clinical Isolates from Vaccine Recipients

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Abstract
Possible biologic and biophysical markers of the Oka vaccine strain of varicella-zoster virus (VZV) were explored. The ratio between the infectivity of the vaccine strain in guinea-pig embryo fibroblasts and that in human embryo fibroblasts was consistently higher than the corresponding ratios for wild-type strains; this result seemed to correlate with the passage history of the vaccine strain in guinea-pig embryo fibroblasts. According to profiles of cleavage of digested DNA by various restriction endonucleases, the mobility of one fragment (K) produced by restriction endonuclease Hpa I was unique to the Oka strain. Nine clinical isolates from vaccine recipients (seven with varicella and two with zoster) were examined by both methods (infectivity and cleavage profiles) to determine whether or not these strains were vaccine derived. The laboratory judgments obtained by the two methods were in agreement and were consistent with clinical conclusions concerning five of the strains. Since the test of relative infectivity is simple and convenient, it is suitable for differentiation of the vaccine strain from other wild-type strains; if the results are not conclusive, profiles of cleavage by Hpa I may be helpful in reaching a definite judgment.