Effectiveness of Bivalent mRNA Vaccines in Preventing Symptomatic SARS-CoV-2 Infection - Increasing Community Access...

Area of Science:

• Immunology
• Vaccinology
• Public Health

Background:

• Bivalent COVID-19 mRNA vaccines targeting ancestral and Omicron BA.4/BA.5 strains were recommended in September 2022.
• Initial recommendations were for individuals aged 12 years and older, later expanded to include children aged 5-11.
• While immunogenicity data existed for BA.1-containing vaccines, clinical efficacy data for BA.4/BA.5 formulations were initially unavailable.

Purpose of the Study:

• To evaluate the effectiveness of the bivalent (Omicron BA.4/BA.5-containing) mRNA booster formulation against symptomatic SARS-CoV-2 infection.
• To assess the impact of time elapsed since the last monovalent vaccine dose on bivalent booster effectiveness.
• To provide real-world data on the protection offered by updated COVID-19 vaccines.

Main Methods:

• Analysis of data from the Increasing Community Access to Testing (ICATT) national SARS-CoV-2 testing program.
• Inclusion of 360,626 nucleic acid amplification tests (NAATs) from adults aged 18 years and older with COVID-19 symptoms.
• Comparison of relative vaccine effectiveness (rVE) between bivalent booster doses and at least two monovalent doses, stratified by age and time since last vaccination.

Main Results:

• Bivalent boosters provided relative vaccine effectiveness (rVE) of 30% (2-3 months post-monovalent) and 56% (≥8 months post-monovalent) in adults aged 18-49 years.
• Similar effectiveness was observed in older age groups: 31% and 48% for ages 50-64, and 28% and 43% for ages ≥65, respectively.
• The benefits of bivalent boosters increased with the time elapsed since the last monovalent vaccine dose.

Conclusions:

• Bivalent mRNA booster doses enhance protection against symptomatic SARS-CoV-2 infection in immunocompetent individuals previously vaccinated with monovalent vaccines.
• The protective benefits of bivalent boosters are more pronounced when administered later after the primary monovalent vaccination series.
• Maintaining up-to-date COVID-19 vaccination status, including receiving eligible bivalent booster doses, is crucial for optimal protection against the virus.