Trends in primary, booster, and updated COVID-19 vaccine readiness in the United States, January 2021-April 2023: Implications for 2023-2024 updated COVID-19 vaccines

Objective: COVID-19 vaccines have mitigated the severity of COVID-19 and its sequelae. The emergence of new SARS-CoV-2 variants and waning immunity conferred by COVID-19 vaccination have necessitated booster and updated COVID-19 vaccines. This study examined trends in vaccine readiness-a composite measure of intention and uptake-for the primary, booster, and 2022-2023 updated (bivalent) COVID-19 vaccines among U.S. adults. Methods: Data from the nationally-representative U.S. Department of Health and Human Services' COVID-19 Monthly Outcome Survey from January 2021 to April 2023 were analyzed (N = 140,180). We conducted pairwise comparisons (weighted t-tests) to assess for significant between-month differences in the proportion of participants in each vaccine-readiness category (vaccine ready, wait and see, and no vaccine intention) for the following outcomes: (1) primary; (2) booster; and (3) updated COVID-19 vaccine readiness. Results: From January 2021 to April 2023, significant increases in the primary vaccine ready group were accompanied by decreases in the wait and see and no vaccine intention groups (p < 0.001). From January to September 2022, the no booster intention group notably increased (p < 0.001), whereas the booster ready group decreased (p < 0.001), and the wait and see group remained stable (p = 0.116). From October 2022 to April 2023, the no updated vaccine intention group increased (p < 0.001), the wait and see group decreased (p < 0.01), and the updated vaccine ready group remained unchanged (p = 0.357). Conclusions: Findings show decreased vaccine readiness for the booster and 2022-2023 updated (bivalent) COVID-19 vaccines relative to the primary COVID-19 vaccines. Implications for the 2023-2024 updated COVID19 vaccines are discussed.