Factors associated with uptake of bivalent mRNA COVID-19 vaccines in a large US health care system.

backgroundBivalent mRNA COVID-19 vaccines were developed to provide protection against the original SARS-CoV-2 strain and Omicron BA.4/BA.5 variants, but uptake in the United States has been low. Sociodemographic disparities in COVID-19 vaccine uptake have been documented, but it is unclear if similar disparities persist among individuals who previously completed a primary series of monovalent COVID-19 vaccine.

methodsWe conducted a retrospective cohort study at Kaiser Permanente Southern California (KPSC) including youth aged 5-17 years and adults aged ≥18 years who were KPSC members and had completed a primary series of monovalent COVID-19 vaccine. Individuals were followed from index date (date of eligibility for bivalent vaccine) to 03/31/2023 to ascertain receipt of any dose of bivalent mRNA COVID-19 vaccine or until disenrollment from KPSC or death. Multivariable robust Poisson regression was conducted to assess the adjusted relative risk and 95 % confidence intervals of factors associated with receipt of bivalent vaccine.

resultsThe final cohorts included 305,339 youth and 2,534,619 adults, of whom 19.5 % and 30.7 %, respectively, had received bivalent COVID-19 vaccine. Factors associated with being more likely to receive bivalent COVID-19 vaccine included older age, Asian race, more prior year outpatient and virtual visits, Charlson score ≥1, and immunocompromised status. Factors associated with being less likely to receive a bivalent COVID-19 vaccine included age 12-17 vs 5-11 years, Hispanic and non-Hispanic Black race/ethnicity, ≥1 prior year inpatient or emergency department visits, prior history of SARS-CoV-2 infection (adults only), Medicaid insurance, and higher neighborhood deprivation index.

conclusionEven among youth and adults who had previously received a primary series of monovalent COVID-19 vaccine, sociodemographic and clinical disparities were observed in receipt of bivalent COVID-19 vaccine. These findings are critical to inform equitable strategies for the implementation of the updated monovalent COVID-19 vaccine targeting the Omicron XBB strain.