Piscirickettsia salmonis, the primary bacterial disease in Chilean salmon farming, necessitates a constant refinement of control strategies. This study hypothesized that the current vaccination strategy for SRS control in the Chilean Atlantic salmon aquaculture industry, which has been in place since 2017 (ALPHA JECT® 5.1 plus LiVac®), solely relies on vaccines formulated with the EM-90 genogroup of P. salmonis (PS-EM-90), triggering a partial cross-immunity response in fish infected with the LF-89 genogroup (PS-LF-89). Relative Percent Survival (RPS) and cell mediated immune (CMI) response were evaluated in Atlantic salmon post-smolts vaccinated with the standard vaccination strategy but challenged with both PS-EM-90 and PS-LF-89, in addition to other vaccination strategies considering primo vaccination and booster with other commercial vaccines and the possible enhancing effects of the combination with a natural immunomodulator (PAQ-Xtract®) administered orally. The intraperitoneal (I.P.) challenge was performed after 2395 degree days (DD) after the start of the immunostimulant delivery, 1905 DD after the primo vaccination, and 1455 DD after the booster vaccination. Unvaccinated fish showed 73.6 and 41.7% mortality when challenged with PS-EM-90 and PS-LF-89, respectively. Fish infected with PS-LF-89 died significantly faster (21 days post infection, dpi) than fish challenged with PS-EM-90 (28 dpi) (p =0.0043) and had a higher probability of death (0.4626) than fish challenged with PS-EM-90. RPS had a significant positive correlation with the PS-EM-90 load of the P. salmonis genogroup (r =0.540, p <0.01) but not with the PS-LF-89 load (r =0.155, p >0.05). This demonstrated that the immunization strategies were more effective in lowering PS-EM-90 loads, resulting in higher survival rates in fish challenged with PS-EM-90. The current industry vaccination strategy recorded a 100% RPS when fish were challenged with PS-EM-90, but the RPS dropped significantly to 77% when fish were challenged with PS-LF-89, meaning that the strategy did not show complete cross protection. The serum concentration of anti-P. salmonis IgM did not show a correlation with the protection of immunization strategies expressed in survival. Low serum IL-12 and high serum IFNγ concentrations showed a correlation with higher bacterial loads and lower survival. Aggregate analysis showed a significant correlation between higher numbers of CD8+cells in the head-kidney, higher fish survival, and a lower bacterial load.