ABSTRACT
Background: Understanding the waning of immunity after booster vaccinations is important to identify which immune-low populations should be prioritized. Methods: We investigated longitudinal cellular and humoral immunity after the third vaccine dose in both high- and low-cellular and humoral immunity groups at the peak immunity phase after the booster vaccination in a large community-based cohort. Blood samples were collected from 1045 participants at peak (T1: median 54 days post-third dose) and decay (T2: median 145 days post-third dose) phases to assess IgG(S), neutralizing activity, and ELISpot responses. Participants were categorized into high/low ELISpot/IgG(S) groups at T1. Cellular and humoral responses were tracked for approximately five months after the third vaccination. Results: In total, 983 participants were included in the cohort. IgG(S) geometric mean fold change between timepoints revealed greater waning in the >79 years age group (T2/T1 fold change: 0.27) and higher IgG(S) fold change in the low-ELISpot group at T1 (T2/T1 fold change: 0.32-0.33) than in the other groups, although ELISpot geometric mean remained stable. Conclusions: Antibody level of those who did not respond well to third dose vaccination waned rapidly than those who responded well. Evidence-based vaccine strategies are essential in preventing potential health issues caused by vaccines, including side-effects.