A/SLOV15 S8 and S13 elicited a serum immune response in ferrets, indicating that immunogenicity depends on replicative fitness.

A cross-section of A/SLOV15 variants underwent immunogenicity testing in ferrets. Groups of 4–12 ferrets were vaccinated with 4.0 Log₁₀ FFU of monovalent V1 (MLAIV-V1), monovalent S3 (MLAIV-S3), monovalent S8 (MLAIV-S8) and monovalent S13 (MLAIV-S13). Four unvaccinated ferrets were also included as controls. Serum immune responses were measured by HAI. Antisera were collected 21 days post-vaccination and titrated against parental V1 virus, containing wt A/SLOV15 HA sequence. MLAIV-V1, MLAIV-S3, MLAIV-S8 and MLAIV-S13 HAI titres were compared to the unvaccinated control animals by performing a Kruskal-Wallis test followed by Dunn’s multiple comparisons test. HAI titres for individual animals are depicted by the scatter plots, median values for each vaccination group are indicated by the columns. Error bars show median with 95% CI, and the dotted line represents the lower limit of detection (LLD). Values below the LLD are plotted as ½ LLD for statistical purposes. P values are indicated as follows: **** P<0.0001 and *** P<0.001.