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A generalization of the rigorous method of regularization is implemented to calculate the complex eigenvalues for a two dimensional arbitrarily shaped acoustically soft cavity with a longitudinal slit. The problem is reduced to the finding of non-trivial solutions of the coupled homogeneous well-conditioned Fredholm second kind infinite systems of linear algebraic equations that are solved numerically by the truncation method. The guaranteed fast convergence of the solution of the truncated system to the exact solution allows one to achieve any pre-determined accuracy by proper choice of truncation number. Formally, the complex eigenvalues coincide with the complex roots of the characteristic equation of the truncated infinite system. All calculations are performed with an accuracy of six significant decimal digits. The algorithm is free from limitations on the slit width, frequency band, and slit location along the bounding contour of a cavity. As an example, the spectrum of the complex eigenvalues for open elliptic cavity with moveable longitudinal slit is accurately investigated for various ellipse eccentricities, including the case of degenerated elliptic cavity—circular cavity. The slit width varies from zero value (closed cavity) to open semi-elliptic cavity.

The COVID-19 pandemic emerged in 2020 and has caused an unprecedented burden to all countries in the world. SARS-CoV-2 continues to circulate and antigenically evolve, enabling multiple reinfections. To address the issue of the virus antigenic variability, T cell-based vaccines are being developed, which are directed to more conserved viral epitopes. We used live attenuated influenza vaccine (LAIV) virus vector to generate recombinant influenza viruses expressing various T-cell epitopes of SARS-CoV-2 from either neuraminidase (NA) or non-structural (NS1) genes, via the P2A self-cleavage site. Intranasal immunization of human leukocyte antigen-A*0201 (HLA-A2.1) transgenic mice with these recombinant viruses did not result in significant SARS-CoV-2-specific T-cell responses, due to the immunodominance of NP366 influenza T-cell epitope. However, side-by-side stimulation of peripheral blood mononuclear cells (PBMCs) of COVID-19 convalescents with recombinant viruses and LAIV vector demonstrated activation of memory T cells in samples stimulated with LAIV/SARS-CoV-2, but not LAIV alone. Hamsters immunized with a selected LAIV/SARS-CoV-2 prototype were protected against challenge with influenza virus and a high dose of SARS-CoV-2 of Wuhan and Delta lineages, which was confirmed by reduced weight loss, milder clinical symptoms and less pronounced histopathological signs of SARS-CoV-2 infection in the lungs, compared to LAIV- and mock-immunized animals. Overall, LAIV is a promising platform for the development of a bivalent vaccine against influenza and SARS-CoV-2.