Influenza viruses cause an acute respiratory infection, especially in the autumn-winter period. They are characterized by a high mutation frequency and cause annual seasonal epidemics. The detection of virus-neutralizing antibodies is an important criterion in the assessment of population immunity and the influenza vaccine effectiveness. In this study, a method for determining the titer of virus-neutralizing antibodies in blood serum has been developed. A new test, called the luciferase neutralization assay, uses measurement of a bioluminescent signal as a detection method. The influenza A reporter viruses of various subtypes were constructed that encode the nanoluciferase protein in the non-structural NS1 protein reading frame. The developed method was used to compare paired sera of volunteers before and after their immunization with a seasonal influenza vaccine. The proposed method was also compared with certified antibody assay methods: neutralization reaction and hemagglutination inhibition reaction. The tests showed a high correlation, while the luciferase neutralization assay reduced the time and simplified the detection procedure. microneutralization, reporter virus, influenza virus, bioluminescence, nanoluciferase The study was supported by the grant of the President of the Russian Federation for young PhDs (no. 075-15-2019-226); and also by the grant of the Government of Saint-Petersburg for undergraduate and graduate students (September 25, 2018, no 124).

Influenza viruses cause acute respiratory infections, especially in the autumn–winter period. They are characterized by a high mutation frequency and cause annual seasonal epidemics. The detection of antibodies that neutralize the virus is an important criterion in the assessment of population immunity and the influenza vaccine effectiveness. In this study, a method for determining the titer of virus-neutralizing antibodies in blood serum has been developed. A new test called the luciferase neutralization assay uses a bioluminescent signal for detection. The assay is based on engineered influenza reporter viruses with various surface antigens and a nanoluciferase reporter protein in the NS1 reading frame. Using the developed method, we studied paired sera of volunteers obtained before and after vaccination. The proposed assay was compared with the conventional antibody assessment methods (microneutralization and hemagglutination inhibition assay); a high degree of correlation was observed. At the same time, the use of the luciferase neutralization assay made it possible to reduce the time required for the analysis and to simplify the detection procedure. Supplementary Information The online version contains supplementary material available at 10.1134/S0003683822070067.