Introduction: The global co-circulation of two influenza B virus genetic lineages known as B/Yamagata and B/Victoria may lead to a mismatch between the circulating virus and the strain recommended for use in influenza vaccines. Little is known about the protective efficacy of unmatched influenza B strains, especially when it comes to live attenuated influenza vaccine. The main purpose of this study was to demonstrate the viability of using live attenuated influenza vaccine developed on B/USSR/60/69 backbone to protect from heterologous influenza B challenge infection.
Methods: To estimate the potential cross-protective activity of mono- and trivalent live attenuated vaccines based on B/Victoria or B/Yamagata genetic lineage virus against a heterological challenge. Ferrets were given one dose of vaccine and then challenged with influenza B virus and monitored for clinical signs associated with influenza infection. Samples of the ferrets’ airways were tested for the presence of challenge virus.
Results: Mono- and trivalent live attenuated influenza vaccines were shown to be safe and cross-protective against genetically different influenza B viruses based on virological and histological data and clinical signs. A lower titer of heterologous challenge virus in the airways of vaccinated ferrets compared to mock-vaccinated animals inoculated with challenge virus was detected. Interestingly, B/Victoria-based vaccines were more cross-protective compared with B/Yamagata-based vaccines.
Conclusion: In the case of mismatches of B component of the trivalent live attenuated influenza vaccine and lineage of the circulating influenza B viruses, one of the options could be using trivalent preparation containing a B/Victoria lineage component.

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