Barriers to initial COVID-19 booster among U.S. adults who completed a primary vaccine series in the CHASING COVID cohort, September 2021 - October 2022

It is crucial to understand factors associated with COVID-19 booster uptake in the U.S. given the updated COVID-19 vaccine recommendations. Using data from a national prospective cohort (N=4,616) between September 2021-October 2022, we examined socioeconomic, demographic, and behavioral factors of initial booster uptake among participants fully-vaccinated with the primary COVID-19 vaccines series. Cox proportional hazards models were used to estimate the associations of each factor with time to initial booster uptake. Most participants (86.5%) reported receiving their initial booster. After adjusting for age, race/ethnicity, education, region, and employment, participants with greater risk for severe COVID-19 had similar booster uptake compared with those with lower risk (aHR: 1.04; 95% CI: 0.95, 1.14). Participants with greater barriers to healthcare (aHR: 0.89; 95% CI: 0.84, 0.96), food insecurity (aHR: 0.82; 95% CI: 0.75, 0.89), and housing instability (aHR: 0.81; 95% CI: 0.73, 0.90) were less likely to report receiving initial booster compared with those without those barriers. Factors motivating the decision to vaccinate changed from safety-related concerns for the primary series to perceived need for the booster. It is key to address economic and health access barriers to achieve equitable COVID-19 vaccine uptake and continued protection against COVID-19.