COVID-19 Vaccine Booster Uptake and Effectiveness Among US Adults With Cancer.

Importance Persons with cancer are at increased risk of severe COVID-19 infection, but the additional benefit of COVID-19 boosters is unclear. Objective To assess COVID-19 vaccine effectiveness (VE) and number needed to vaccinate (NNV) among persons with cancer of an additional dose of the monovalent COVID-19 vaccine. Design, Setting, and Participants Retrospective cohort study conducted in 4 health care systems in the US among persons with cancer receiving chemotherapy or immunotherapy. Statistical analysis was conducted between March 2023 and August 2024. Exposures Receipt of an additional dose of the monovalent COVID-19 vaccine before January 1, 2022, with follow-up until August 31, 2022, and the bivalent COVID-19 vaccine from September 1, 2022, to August 31, 2023. Main Outcomes and Measures COVID-19 hospitalization, diagnosed COVID-19, and COVID-19-related intensive care unit (ICU) admission. Results Among 72 831 persons with cancer (17 922 female individuals [24.6%]), 69% received a monovalent booster by January 1, 2022. During 34 006 person-years of follow-up, the COVID-19 hospitalization rate was 30.5 per 1000 person-years among patients who received a monovalent booster vs 41.9 per 1000 person-years among patients who received the primary series alone, with an adjusted VE of 29.2% (95% CI, 19.9%-37.3%) and NNV to prevent 1 COVID-19 hospitalization of 166 (95% CI, 130-244). There was also significant VE to prevent diagnosed COVID-19 (8.5% [95% CI, 3.7%-13.0%]) and COVID-19-related ICU admission (35.6% [95% CI, 20.0%-48.3%]). Among 88 417 persons with cancer (24 589 female individuals [27.8%]) with 81 027 person-years of follow-up during the bivalent period, patients who received this booster (38%) had a COVID-19 hospitalization rate of 13.4 per 1000 person-years vs 21.7 per 1000 person-years among persons who did not receive a bivalent vaccine, with an adjusted VE of 29.9% (95% CI, 19.4%-39.1%) and NNV to prevent 1 COVID-19 hospitalization of 451 (95% CI, 345-697); the adjusted VE was 30.1% (95% CI, 7.7%-47.0%) to prevent COVID-19-related ICU admission. Conclusions and Relevance In this retrospective cohort study, COVID-19 booster vaccinations were associated with significant protection against severe COVID-19, with a favorable NNV among persons with cancer. However, uptake of COVID-19 vaccine boosters was low, and interventions are therefore justified to increase COVID-19 uptake in this high-risk population.