Effectiveness of the 2023-2024 Omicron XBB.1.5-containing mRNA COVID-19 Vaccine (mRNA-1273.815) in Preventing COVID-19-related Hospitalizations and Medical Encounters Among Adults in the United States

Background: This study aimed to evaluate the vaccine effectiveness (VE) of mRNA-1273.815, a 2023-2024 Omicron XBB.1.5-containing mRNA COVID-19 vaccine, at preventing COVID-19-related hospitalizations and any medically attended COVID-19 in adults.

Methods: In a linked electronic health record-claims dataset, we identified US adults (≥18 years) who received the mRNA-1273.815 vaccine (exposed cohort) between 12 September and 15 December 2023, matched 1:1 to individuals who did not receive a 2023-2024 updated COVID-19 vaccine (unexposed cohort). Cohorts were balanced using inverse probability of treatment weighting on demographics, vaccination and infection history, and underlying medical conditions. Study cohorts were followed until 31 December 2023 for COVID-19-related hospitalizations and medically attended COVID-19. Cox regression was used to estimate hazard ratios and VE. Subgroup analyses were performed for adults ≥50 years, adults ≥65 years, and individuals with underlying medical conditions.

Results: Overall, 859 335 matched pairs of mRNA-1273.815 recipients and unexposed adults were identified. The mean (standard deviation) age was 63 (16) years. More than 60% of individuals in both cohorts had an underlying medical condition. Among the overall adult population, VE was 60.2% (95% confidence interval, 53.4-66.0) against COVID-19-related hospitalization and 33.1% (30.2-35.9) against medically attended COVID-19 over a median follow-up of 63 (interquartile range: 44-78) days. VE estimates by age and underlying medical conditions were similar.

Conclusions: These results demonstrate the significant protection provided by mRNA-1273.815 against COVID-19-related hospitalizations and any medically attended COVID-19 in adults, regardless of vaccination history, and support Centers for Disease Control and Prevention recommendations to stay up-to-date with COVID-19 vaccination to prevent COVID-19-related outcomes, including hospitalizations.