Relative vaccine effectiveness (rVE) of mRNA COVID-19 boosters in the UK vaccination programme, during the Spring-Summer (monovalent vaccine) and Autumn-Winter 2022 (bivalent vaccine) booster campaigns: a prospective test negative case-control study

BackgroundUnderstanding the relative vaccine effectiveness (rVE) of new COVID-19 vaccine formulations against SARS-CoV-2 infection is an urgent public health priority. A precise comparison of the rVE of monovalent and bivalent boosters given during the 2022 Spring-Summer and Autumn-Winter campaigns, respectively, in a defined population has not been reported. We therefore assessed rVE against hospitalisation for the Spring-Summer (fourth vs third monovalent mRNA vaccine doses) and Autumn-Winter (fifth BA.1/ancestral bivalent vs fourth monovalent mRNA vaccine dose) boosters.MethodsA prospective single-centre test-negative design case-control study of ≥75 year-olds hospitalised with COVID-19 or other acute respiratory disease. We conducted regression analyses controlling for age, gender, socioeconomic status, patient comorbidities, community SARS-CoV-2 prevalence, vaccine brand and time between baseline dose and hospitalisation.Results682 controls and 182 cases were included in the Spring-Summer booster analysis; 572 controls and 152 cases for the Autumn-Winter booster analysis. A monovalent mRNA COVID-19 vaccine as fourth dose showed rVE 46·9% (95% confidence interval [CI] 14·4-67·3) versus those not boosted. A bivalent mRNA COVID-19 vaccine as fifth dose had rVE 46·4% (95%CI 17·5-65), compared to a fourth monovalent mRNA COVID-19 vaccine dose.InterpretationBoth fourth monovalent and fifth BA.1/ancestral mRNA bivalent COVID-19 vaccine doses demonstrated benefit as a booster in older adults. Bivalent mRNA boosters offer equivalent protection against hospitalisation with Omicron infection to monovalent mRNA boosters given earlier in the year. These findings support the current UK immunisation programme that advises the use of bivalent booster doses.