Kinetics of antibodies and risk of respiratory syncytial virus infection: a longitudinal cohort in Taizhou City, eastern China

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BACKGROUND: Respiratory syncytial virus (RSV) causes recurrent infections throughout life. Yet, the form and durability of antibody-mediated protection induced by infection remained poorly understood. METHODS: We conducted a longitudinal cohort study in Taizhou City, China. Participant age distribution approximately reflected the age structure of population in Taizhou. Blood samples were collected at baseline (March 12, 2023) and four follow-up visits (May 7-26, 2023, August 13-23, 2023, November 12, 2023, and June 2-3, 2024). Serum-specific RSV pre-fusion F (PreF) protein antibody titres were measured for all samples, and neutralising antibodies against RSV strain A2 and RSV strain B were assessed in a subset. Using a Bayesian inference framework and reversible-jump Markov Chain Monte Carlo, we recovered individual infection histories, estimated population-level RSV incidence, and characterised antibody dynamics from longitudinal PreF titres. We also estimated the correlates of protection (COP) by quantifying the relationship between PreF antibody titres and infection risk. RESULTS: A total of 508 individuals were included. Over the study period, two RSV epidemic waves were observed: the first wave between May and November 2023 and the second from February to May 2024. We estimated seasonal RSV infection rates of 4-7% in the community-based population. Post-infection immunity responses were most robust in young children ≤ 5 years and weakest in adults ≥ 75 years, with peak fold rises in antibody titres of 29.4 and 5.4, respectively. The post-infection antibody titres declined substantially, with fourfold rises sustained for an average of 128 days (95% credible interval of 21-281). The probability of protection given exposure increased with higher PreF titres across all age groups. However, the predictive performance of PreF titres as a COP varied markedly by age: titres strongly predicted protection in young children but showed weaker discrimination in older children and adults, and minimal predictive value in the oldest adults. CONCLUSIONS: These results revealed age-related differences in the durability and protective value of natural infection-elicited RSV PreF antibody responses, emphasising the importance of age-specific prevention strategies.

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