Comparative 60-day effectiveness of bivalent versus monovalent mRNA vaccines in Shelby County: a population-level...

Two monovalent mRNA vaccines, available in December 2020, were demonstrated to have high efficacy against both the original SARS-CoV-2 strain and variants circulating through the summer and into the fall of 2021. In the context of the Omicron/BA.1 variant, which was predominant from late fall 2021 into winter of 2022 in the United States, and subsequent Omicron subvariants that have been predominant thereafter, vaccine effectiveness of the monovalent mRNA vaccine option is attenuated.

We aim to investigate the relative effectiveness of the bivalent booster compared to the monovalent booster against SARS-CoV-2 infection in the 60 days following administration in Shelby County, TN.

This observational population-based cohort study utilizes COVID-19 surveillance data to identify adults who were vaccinated with a monovalent booster dose between August 1, 2022 and August 30, 2022 or a bivalent booster dose between September 1, 2022 and September 30, 2022. Both groups were followed for COVID-19 status for 60 days from their administration date.

We calculated incidence rates with 95% confidence intervals and propensity-adjusted hazard ratios with 95% confidence intervals of COVID-19 diagnosis in the 60 days following administration of the booster dose between the bivalent group and the monovalent group. Stratified analysis was conducted by age group (18-34, 35-64, and 65+ years old).

The incidence of reported SARS-CoV-2 infection was substantially higher for those who received the monovalent booster, across age groups. Overall, we observed a 51% lower hazard of infection during the study period among those who received the bivalent booster, compared to the monovalent booster.

These results support and extend prior findings that the bivalent booster dose may be more effective in preventing infection against the Omicron sub-variants of SARS-CoV-2.