Age-specific antibody profiles of respiratory syncytial virus after COVID-19 pandemic: a sero-epidemiological survey in Taizhou City, Eastern China.

BACKGROUND: The generalizability of the current quantitative assessments of age-specific RSV antibody levels remains unclear in China. We aimed to comprehensively understand the RSV immune profile at the population level and identify related factors. METHODS: We conducted a community-based cross-sectional sero-epidemiological study in Taizhou City, Eastern China, from June 2 to 30, 2024, and assessed RSV pre-F IgG antibody titres. We employed generalized linear models to identify factors linked to antibody titres and used a generalized additive model to determine RSV seropositivity risk. The serocatalytic model was further used to estimate the force of infection (FOI) based on age-specific seroprevalence data. RESULTS: Among 1303 individuals aged 16 months to 93 years, toddlers (younger than 2 years) had the lowest geometric mean titres (GMTs) of RSV pre-F IgG antibodies, which was 591.9 (95% confidence interval [CI], 106.5-3291.1). The GMTs increased annually by 2.038-fold (0.842-4.011), attaining a titre of 6133.9 (4639.3-8110.2) by the age of 4. The seroprevalence (using titre > 200 as the threshold) surged sharply with age, from 46.1% (42.2-50.2) at 1 year of age to 91.5% (88.9-93.8) at age 4, with an estimated FOI of 0.618 (0.547-0.697). Children residing in households with over four members correlated with a heightened risk of seropositivity within the first 4 postnatal year compared to those in households with four or fewer members (adjusted odds ratio, aOR: 1.954, 1.082-3.529). Age was significantly associated with GMTs in the elderly individuals (aged 65 and above), with an estimated annual increment of 0.019-fold (0.004-0.034). Elderly with underlying diseases demonstrated a 0.203-fold (0.036-0.341) reduction in GMTs compared to those without such conditions. CONCLUSIONS: An early age-dependent pattern in RSV serostatus is observed, and the seroprevalence increased with age. Low antibody titres in early-life period and immunity impairment in the elderly due to underlying diseases emphasize the need to protect younger children and the elderly, from RSV infections. CLINICAL TRIAL: Not applicable.