Assessment of an end-point microassay for varicella vaccine

For routine control purposes, a statistical analysis was performed on the results obtained in titrations of varicella vaccine using a cytopathic effect microassay in a continuous line of monkey kidney cells. Although the results were lower than those obtained by conventional plaque assay, the end-point titres were quite reliable. The within-test variation was very small compared with test-to-test differences and the reference and vaccine titres were highly correlated. Expression of titre in relation to the reference is of value in this microsystem. The microassay has the advantage of economy and less labour. Staining of the microplates ensured convenience and reliability of reading comparable with that of plaque counting.