Fig 2.

Comparison of HI titers of serum samples in chickens that were immunized with the LaSota vaccine strain and challenged 21 days later with the indicated virulent strains (AKO18, 488MT, GB Texas [GBT], and Fontana). Sera were taken immediately prior to challenge (Pre-) and at 14 days postchallenge (Post-) of survivor birds. The titers in serum samples against the immunizing virus (LaSota) and each respective challenge virus were assayed to compare any increase of serum HI titer. This increase of titer may indicate replication of challenge virus in the vaccinated birds.