Humoral response dynamics following inactivated SARS-CoV-2 vaccination and their association with subsequent infection and symptoms in individuals with and without prior SARS-CoV-2 infection: evidence from Sichuan Province, China.

Unlabelled: This study integrated multisource longitudinal data with trajectory modeling to delineate the heterogeneity of humoral immune dynamics induced by inactivated SARS-CoV-2 vaccinations and their clinical implications for subsequent SARS-CoV-2 infection outcomes in 205 individuals from Sichuan Province, China. We found that preexisting infection status served as the dominant stratifier of antibody trajectory divergence across the cohort. Additionally, among individuals without prior infection before the vaccine cohort, we identified five distinct immune response patterns with clinical implications. An age-associated "minimal response" subtype was associated with an increased risk of prolonged recovery time, sore throat, and limb pain in subsequent infections. In contrast, a subtype characterized by a marked increase in S-Igs titers after the booster dose exhibited fewer symptoms, with a lower likelihood of experiencing fever and fatigue. What is more, for those with prior infection, clinical data-including viral shedding duration and total antibody levels 15 days after discharge from the initial infection-could provide valuable insights into the subsequent risk of reinfection.

Importance: To better identify vulnerable populations in epidemic surveillance and predict their clinical manifestations post-infection for accurate diagnosis and effective management, it is vital to understand the intrinsic dynamic immune patterns among individuals and how these trajectory patterns relate to future infections and associated symptoms. In the post-COVID-19 era, conducting nuanced analyses remains of great significance, especially as longer-term observational data become available. This is the first finding from China that illustrates the dynamic characteristics of the immune response following inactivated COVID-19 vaccination over an extended observation period, including information on following infection and symptoms. These data are particularly valuable as no participants experienced COVID-19 infection during the vaccine cohort follow-ups, meaning their antibody levels solely reflect the intrinsic dynamic immune patterns triggered by the inactivated COVID-19 vaccines.