To identify the best infection strategy, Sf-9 cells were infected at cell concentrations at infection (CCI) of 1 and 2 × 106 cell/mL with recombinant baculovirus rBac 1 (Table 1) using multiplicities of infection (MOI) of 0.1 and 1 pfu/cell, and their growth and S protein expression kinetics assessed in small-scale shake flasks (SF) (Figure 1). This evidence concerns the gene PROS1 and infection.