ABSTRACT At this stage in the COVID-19 pandemic, a critical issue has become to understand how long individuals can maintain strong immunity from vaccinations, which groups are at highest risk, and what malleable social, behavioral, and psychological factors can promote optimal maintenance. Fortunately, due to our initial R24 supplement, we have launched a remarkable study (The BOOST Study) designed to address these questions by examining telomere length, stress, and behavioral factors as predictors with 94% adherence. We have the opportunity to examine response to a second vaccination with the same design in the same cohort, by adding data collection six months after the booster vaccination. We will be the first study to be able to examine the trajectory of immune responses at 3 critical post vaccination time points over the first year of vaccination roll out. We can address our original predictors, leukocyte telomere length and chronic stress and age interactions (Aims 1) as predictors of COVID-19 vaccination response trajectories (based on antibody response at 6 weeks, and maintenance of antibodies at 6 months and now, newly, 6 months after booster shot). Further, we can now test how these factors predict breakthrough infections (Aim 2). Lastly, this supplement allows us to collect cells enabling us to apply for an R01 to examine T cell responses to vaccination (Aim 3), a critical part of immune protection but rarely studied due to the costs of these in vitro cell assays. Now that COVID-19 has become endemic, these questions are of critical importance to public health for decades to come.