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.