FIG 2.

Immunization via the i.p. route yields the highest levels of circulating antipoxvirus antibodies. Plasma was isolated by retro-orbital bleeding from mice that had been immunized with VACV 30 days earlier via the indicated routes. Levels of circulating antibodies were quantified using plates coated with VACV at 1 × 10⁶ PFU per well. Antibody titers were determined by calculating the 50% effective concentration (EC₅₀) using nonlinear regression in GraphPad Prism (version 5.0a). Values calculated above or below the dilution range were set to 1/30 and 1/10,000, respectively. **, P value < 0.01; ***, P value < 0.001. The solid black lines represent the mean value within each group. Statistical analysis was performed using GraphPad Prism. Each data point represents one individual mouse. Black data points are from one individual experiment, and blue data points are from a second independent trial.