Strength and durability of RSV pre-fusion F IgG following infection and exposure in a household cohort, 2014-2022.

Abstract

Background: Little is known about the strength and durability of protection (CoP) provided by pre-F IgG after RSV infection/exposure.

Methods: We analyzed 1,019 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 pre-infection/exposure IgG and risk of RT-PCR-confirmed infection. We compared pre- to post-infection/exposure IgG geometric mean concentration (GMC) 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<0.05) and significantly higher levels after infection (p<0.05). A one-unit increase in log4 pre-infection IgG decreased the risk of infection by 25% (p<0.05). Among 58 cases with pre- to post-RSV GMC 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 one month (p<0.001).

Conclusions: Pre-F IgG is a reliable CoP 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 individuals with the highest risk of severe disease are protected throughout RSV season.