2.4. Calculation of Standard NT50 Values

For screening relatively low titer samples, a standard dilution scheme of four replicates for each sample were spread across two plates (Figure 1A). The NT₅₀ value was determined individually for each set of two plates based on the virus-positive control wells. To determine the 50% infection rate for a plate, the average of 12 observations of positive control wells was multiplied by 0.50. The output of each step-wise dilution was the average of the four replicates across two plates. The sample dilution output was compared against the calculated NT₅₀ cutoff value for the duplicate plates, and the highest dilution to achieve an infection of ≤50% was considered the NT₅₀ titer for the sample. Results are reported as the reciprocal dilution.