Trends in development of the influenza vaccine with broader cross-protection.

Influenza A viruses cause in humans acute respiratory infections, which spread yearly in the form of epidemics or pandemics. A high variability and broad host specificity of influenza A viruses are the main reasons of repeated influenza infections. Therefore, no effective prevention against influenza is available today. The main problem of insufficient protection efficacy is that virus-neutralizing antibodies induced by current vaccines are closely strain-specific and the vaccines need to be updated each year. Therefore, various novel approaches to vaccine preparation have been developed with the aim to widen the spectrum of their efficacy. These approaches comprise using new adjuvants as components of the inactivated vaccines, new techniques of live attenuated vaccine preparation (reverse genetics), and new vaccine design focused on the conserved antigens of influenza A viruses inducing protective immunity not only against the influenza viruses antigenically similar (homologous) to vaccine strains, but also against heterologous viruses, even of different subtypes. In this review examples of new approaches to the induction of intersubtype immunity against influenza and their utilization in vaccine preparation are described.