Figure 5.

Comparisons of respiratory syncytial virus (RSV) plaque reduction–neutralizing antibody titer (PRNT) after immunization (Day 56) and after the surveillance period, with titers expressed as reciprocal log₂. Dots of the same color represent identical participants but at different time points. Open circles are postimmunization PRNTs; closed circles are postsurveillance PRNTs. Lines indicate the mean PRNT. Red scatterplots: anamnestic antibody responses following exposure to wild-type (wt) RSV in 36 vaccinees who developed a greater than or equal to fourfold PRNT response after immunization, and also had a greater than or equal to fourfold PRNT response during the surveillance period, indicating exposure to wt RSV. PRNTs after immunization (red open circles, mean 6.4 log₂, geometric mean titer = 84) are compared with PRNTs following surveillance (red closed circles, mean 10.2 log₂, 1,176). Blue scatterplots: durability of neutralizing antibody responses following vaccination in 83 vaccinees who developed a greater than or equal to fourfold PRNT response after immunization but did not have a greater than or equal to fourfold PRNT response during the surveillance period, indicating they were not exposed to wt RSV. PRNTs after immunization (open blue circles, mean 6.8 log₂, 111) are compared with PRNTs after surveillance (closed blue circles, mean 6.3 log₂, 79). Orange and black scatterplots: PRNTs induced by vaccination are comparable to those induced by wt RSV infection. The mean PRNT on Day 56 following vaccination among all 122 vaccinees was 6.7 log₂ (orange scatterplot), and the postsurveillance PRNT among 41 placebo recipients exposed to wt RSV during surveillance was 7.0 log₂ (black scatterplot).