FIG 4.

One hundred serum samples from children 6 to 18 months of age were tested for anti-RSV-N-specific IgG antibodies. (A) RLU values for each sample (◊) tested are plotted versus the age at which the sample was collected; ■, mean for the group. Of the 100 samples tested, 36 samples were found to be negative for anti-RSV-N IgG antibodies using a cutoff value of 8,000 RLU obtained from testing IgGΔ (mean + 5 SD), as shown by the horizontal dashed line. (B) Of the 36 seronegative samples, 12 were obtained from subjects at 9 months of age, and these subjects had paired samples obtained at 15 or 18 months of age. Seven of the 12 paired samples tested positive at follow-up, while 5 of 12 remained negative. (C) ND₅₀ titers are shown for 11 of the 12 paired samples tested using a PRN assay versus RSV-A2.