Plumb, Ian D.Briggs Hagen, MelissaWiegand, RyanDumyati, GhinwaMyers, ChristopherHarland, Karisa K.Krishnadasan, AnushaJames Gist, JadeAbedi, GlenFleming-Dutra, Katherine E.Chea, NoraLee, Jane E.Kellogg, MelissaEdmundson, AlexandraBritton, AmberWilson, LucyLovett, Sara A.Ocampo, ValerieMarkus, Tiffanie M.Smithline, Howard A.Hou, Peter C.Lee, Lilly C.Mower, WilliamRwamwejo, FernandSteele, Mark T.Lim, Stephen C.Schrading, Walter A.Chinnock, BrianBeiser, David G.Faine, BrettHaran, John P.Nandi, UtsavChipman, Anne K.LoVecchio, FrankEucker, StephanieFemling, JonFuller, MatthewRothman, Richard E.Curlin, Marcel E.Talan, David A.Mohr, Nicholas M.2024-06-112024-06-112024-04-11Plumb, Ian D., Melissa Briggs Hagen, Ryan Wiegand, Ghinwa Dumyati, Christopher Myers, Karisa K. Harland, Anusha Krishnadasan, et al. “Effectiveness of a Bivalent MRNA Vaccine Dose against Symptomatic SARS-CoV-2 Infection among U.S. Healthcare Personnel, September 2022–May 2023.” Vaccine 42, no. 10 (April 11, 2024): 2543–52. https://doi.org/10.1016/j.vaccine.2023.10.072.https://doi.org/10.1016/j.vaccine.2023.10.072http://hdl.handle.net/11603/34547Background: Bivalent mRNA vaccines were recommended since September 2022. However, coverage with a recent vaccine dose has been limited, and there are few robust estimates of bivalent VE against symptomatic SARS-CoV-2 infection (COVID-19). We estimated VE of a bivalent mRNA vaccine dose against COVID-19 among eligible U.S. healthcare personnel who had previously received monovalent mRNA vaccine doses. Methods: We conducted a case-control study in 22 U.S. states, and enrolled healthcare personnel with COVID-19 (case-participants) or without COVID-19 (control-participants) during September 2022–May 2023. Participants were considered eligible for a bivalent mRNA dose if they had received 2–4 monovalent (ancestral-strain) mRNA vaccine doses, and were >=67 days after the most recent vaccine dose. We estimated VE of a bivalent mRNA dose using conditional logistic regression, accounting for matching by region and four-week calendar period. We adjusted estimates for age group, sex, race and ethnicity, educational level, underlying health conditions, community COVID-19 exposure, prior SARS-CoV-2 infection, and days since the last monovalent mRNA dose. Results: Among 3,647 healthcare personnel, 1,528 were included as case-participants and 2,119 as control-participants. Participants received their last monovalent mRNA dose a median of 404 days previously; 1,234 (33.8%) also received a bivalent mRNA dose a median of 93 days previously. Overall, VE of a bivalent dose was 34.1% (95% CI, 22.6%–43.9%) against COVID-19 and was similar by product, days since last monovalent dose, number of prior doses, age group, and presence of underlying health conditions. However, VE declined from 54.8% (95% CI, 40.7%–65.6%) after 7–59 days to 21.6% (95% CI 5.6%–34.9%) after >=60 days. Conclusions: Bivalent mRNA COVID-19 vaccines initially conferred approximately 55% protection against COVID-19 among U.S. healthcare personnel. However, protection waned after two months. These findings indicate moderate initial protection against symptomatic SARS-CoV-2 infection by remaining up-to-date with COVID-19 vaccines.10 pagesen-USThis work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.Public Domainhttps://creativecommons.org/publicdomain/mark/1.0/BivalentCOVID-19COVID-19 vaccinesHealthcare personnelmRNA vaccinesSARS-CoV-2Vaccine effectivenessText