Effectiveness and durability of mRNA-1273 BA.4/BA.5 bivalent vaccine (mRNA-1273.222) against SARS-CoV-2 BA.4/BA.5 and XBB sublineages (preprint)

ABSTRACT

Background: Emerging SARS-CoV-2 sublineages continue to cause serious COVID-19 disease, but most individuals have not received COVID-19 vaccine for >1 year. Assessment of long-term effectiveness of bivalent COVID-19 vaccines against circulating sublineages is important to inform the potential need for vaccination with updated vaccines. Methods: In this test-negative study at Kaiser Permanente Southern California, sequencing-confirmed BA.4/BA.5- or XBB-related SARS-CoV-2-positive cases during 9/1/2022-6/30/2023 were matched 13 to SARS-CoV-2-negative controls. We assessed mRNA-1273 bivalent relative (rVE) and absolute vaccine effectiveness (VE) compared to [≥]2 or 0 doses of original monovalent vaccine, respectively. Outcomes were BA.4/BA.5- or XBB-related infection, emergency department/urgent care (ED/UC) encounters, and hospitalization. Results: The rVE analysis included 20,966 cases and 62,898 controls. rVE (95%CI) against BA.4/BA.5 at 14-60 days and 121-180 days was 52.7% (46.9-57.8%) and 35.5% (-2.8%-59.5%) for infection, and 59.3% (49.7-67.0%) and 33.2% (-28.2-68.0%) for ED/UC encounters. For BA.4/BA.5-related hospitalizations, rVE was 71.3% (44.9-85.1%) and 52.0% (-1.2-77.3%) at 14-60 days and 61-120 days, respectively. rVE against XBB at 14-60 days and 121-180 days, was 48.8% (33.4-60.7%) and -3.9% (-18.1-11.3%) for infection, 70.7% (52.4-82.0%) and 15.7% (-6.0-33.2%) for ED/UC encounters, and 87.9% (43.8-97.4%) and 57.1% (17.0-77.8%) for hospitalization. Results for VE and subgroup analyses (age, immunocompromise, and previous SARS-CoV-2 infection) were similar to rVE analyses. Conclusions: rVE of mRNA-1273 bivalent vaccine against BA.4/BA.5 and XBB infections, ED/UC encounters, and hospitalizations waned over time. Periodic adjustment of vaccines to target emerging variants and revaccination may be important in reducing COVID-19 morbidity and mortality.