Fluorometric assay for the measurement of viral neuraminidase in influenza vaccines.

Influenza viruses have two surface glycoproteins: haemagglutinin and neuraminidase which are capable of inducing a significant antibody response following vaccination. All neuraminidases from different strains of influenza A and B viruses are able to hydrolyse alpha-ketosidic linkages between N-acetylneuraminic (sialic) acid and other carbohydrates. In this report, the neuraminidase activity was assayed in various influenza vaccines by using a fluorogenic substrate: the sodium salt of 2'-(4-methylumbelliferyl)-alpha-D-N-acetylneuraminic acid. This method was reliable (variation less than 8%) and more sensitive (100 to 1000 times) in less time (incubation time = 15 min) than the Warren assay. Therefore, the method is suitable for the control of the sialidase activity during the processing of influenza vaccines.