Limited protective immunity to respiratory syncytial virus and pertussis among adults and healthcare workers in South Korea: A seroepidemiologic study

Respiratory syncytial virus (RSV) and pertussis remain important causes of community outbreaks and nosocomial transmission. However, age-stratified data on protective immunity in the general adult population and baseline immunity among healthcare workers (HCWs) in high-risk hospital departments are limited. We conducted a cross-sectional study among adults undergoing routine health checkups (n = 136) and a prospective cohort study of HCWs in the emergency department, pediatric, infectious disease, and pulmonology wards (n = 118). Antibodies indicative of protective immunity against RSV (pre-fusion IgG) and pertussis (anti-pertussis toxin IgG) were measured by ELISA using predefined thresholds. HCWs provided paired sera before and after the epidemic season (November and March) to assess seroconversion. Among health checkup examinees, RSV protective seroprevalence was 17.6% (16.9% intermediate, 0.7% high), highest in those aged ≥70 y (31.3%), while geometric mean titers (GMTs) were comparable across age groups. Pertussis protective seroprevalence was 13.2%, all within the intermediate range, without a significant age-related trend. Among HCWs, baseline RSV protective seroprevalence was 5.1%, with one seroconversion (0.8%) observed during follow-up. Pertussis protective seroprevalence among HCWs was 6.8%, with no confirmed infection-related seroconversion. GMTs for both pathogens were similar across departments. Protective immunity against RSV and pertussis was limited in both the general adult population and HCWs, indicating substantial susceptibility to seasonal and nosocomial transmission. These findings support strengthening adult pertussis booster strategies and highlight the need for further studies to evaluate targeted RSV vaccination approaches for HCWs in high-risk clinical settings.