ACTB and infection: On the contrary, the normalized expression level of IgM at two weeks post-vaccination was higher than at other periods of vaccination and infection when using 18SrRNA, ACTB, EF1A, ACTB and EF1A together as the reference genes, respectively (Figure 5), which was consistent with the IgM antibody titers of the rSip-group detected by ELISA (Table 4).