Strength and Durability of Respiratory Syncytial Virus Prefusion F Immunoglobulin G Following Infection and Exposure in a Household Cohort, 2014-2022.

Background: Little is known about the strength and durability of protection provided by prefusion F (pre-F) immunoglobulin G (IgG) after respiratory syncytial virus (RSV) infection/exposure.

Methods: We analyzed 1019 sera from 422 individuals in 173 households, collected 365 days before and after RSV infection or exposure (2014-2022), from a longitudinal cohort with active respiratory infection surveillance. IgG against RSV pre-F was measured by electrochemiluminescence assay. We used a Cox model, adjusted for age, to assess the association between log4 preinfection/exposure IgG and risk of infection. We compared pre- and postinfection/exposure IgG geometric mean concentration increases among cases and household contacts to identify asymptomatic infections. Generalized additive mixed models predicted IgG concentrations over time.

Results: We identified 113 confirmed RSV cases and 377 exposed household contacts. Cases had significantly lower pre-F IgG before infection (P < .05) and significantly higher levels after infection (P < .05). A 1-unit increase in log4 preinfection IgG decreased the risk of infection by 25% (P < .05). Among 58 cases with pre- to post-RSV geometric mean concentration increases, the mean fold increase was 1.12. Eight individuals without confirmed infections had ≥1.12-fold increases and were classified as probable asymptomatic infections. Cases had the highest IgG concentrations after infection, peaking at 1 month (P < .001).

Conclusions: Pre-F IgG is a reliable correlate of protection for RSV infection risk. We found that RSV pre-F IgG-mediated protection starts to wane 6 months after infection. Therefore, scheduling of RSV vaccination should be evaluated so that individuals with the highest risk of severe disease are protected throughout the RSV season.