(300) Effectiveness of mRNA-1273 Bivalent (original and omicron BA.4/BA.5) COVID-19 Vaccine Against Hospitalizations for COVID-19, Medically Attended SARS-CoV-2 Infections, and COVID-19 Hospital Deaths in the United States

Publication Number: 1290

Background: The bivalent (original and Omicron BA.4/BA.5) mRNA-1273 COVID-19 vaccine was authorized to protect against Omicron BA.4/BA.5. Real-world evidence evaluating its effectiveness is scarce.

Objectives: To evaluate the vaccine effectiveness (VE) of mRNA-1273 bivalent vaccine in preventing hospitalization for COVID-19, medically attended SARS-CoV-2 infection, and COVID-19 hospital death.

Methods: We conducted a matched cohort study among Kaiser Permanente Southern California members. The exposed cohort included individuals aged ≥18 years and 6-17 years who received mRNA-1273 bivalent vaccine during 8/31/2022-12/31/2022 and 10/12/2022-12/31/2022, respectively. The unexposed cohort included individuals who did not receive any bivalent mRNA vaccine but received ≥2 doses of any monovalent mRNA vaccine, or individuals who did not receive any COVID-19 vaccine. Unexposed individuals were matched to exposed individuals on age, sex, and race/ethnicity, and were assigned an index date equal to the bivalent vaccination date of their matched counterpart. Follow-up began 14 days after the index date and ended at the earliest date of membership termination, death, receipt of COVID-19 vaccine, or 1/31/2023. The outcomes included hospitalization for COVID-19 (primary outcome, identified by a pre-determined algorithm and confirmed by manual chart review), medically attended SARS-CoV-2 infection (positive SARS-CoV-2 molecular or antigen test, and a COVID-19-related encounter), and COVID-19 hospital death. Cox proportional hazards regression was used to estimate adjusted hazard ratios (aHR) comparing incidence of outcomes between the exposed and unexposed cohorts. Relative vaccine effectiveness (rVE) (%) and absolute VE (%) were estimated as (1-aHR) x 100.

Results: The study included 290,292 exposed individuals, 580,584 unexposed individuals who received ≥2 doses of any monovalent mRNA vaccine, and 204,665 unvaccinated individuals. Compared to recipients of ≥2 monovalent mRNA doses, the rVE of mRNA-1273 bivalent vaccine against hospitalization for COVID-19 was 70.3% (95% CI: 64.0-75.4%). The rVE was 64.7% (44.0-77.7%) in immunocompromised individuals, compared to 71.3% (64.5-76.7%) in immunocompetent individuals. The rVE against medically attended SARS-CoV-2 infection was 35.9% (32.7-39.0%) overall, and 55.0% (50.8-58.8%) against infection requiring emergency department/urgent care (ED/UC). The rVE against COVID-19 hospital death was 82.7% (63.7-91.7%). Compared to unvaccinated individuals, the VE against hospitalization for COVID-19 was 82.8% (78.8-86.0%). The VE against medically attended SARS-CoV-2 infection was 10.7% (4.4-16.6%) overall, and 55.4% (50.3-60.1%) against infection requiring ED/UC. The VE against COVID-19 hospital death was 89.7% (77.7-95.2%).

Conclusions: The mRNA-1273 bivalent booster provides additional protection against hospitalization for COVID-19, medically attended SARS-CoV-2 infection, and COVID-19 hospital death.