Detection of antibodies against neuraminidase (NA) of A/California/07/2009 (H1N1) influenza virus in blood sera of volunteers after the immunization with live monovalent influenza vaccine (LIV). Neuraminidase enzyme activity inhibition by antibodies test with reassortant strain A(H7N1) containing NA of pandemic strain was used. Anti-neuraminidase IgG antibodies against whole reassortant virus A(H7N1) and purified NA of A/California/07/2009 (H1N1) strains were determined by enzyme immunoassay (EIA). After two immunizations with LIV of seronegative individuals a 1.5 times mean increase of antibodies against homologous neuraminidase was detected (by hemagglutinin inhibition reaction). The high level of anti-neuraminidase antibodies were detected in individuals that had been naturally infected. A correlation between anti-neuraminidase IgG antibody titers obtained in EIA with whole reassortant virus A(H7N1) and purified protein was demonstrated. Modified sialidase activity inhibition method and EIA with reassortant diagnostic strain can be applied to evaluate anti-neuraminidase antibodies.