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. 2022 Nov 28;226(11):1924-1933.
doi: 10.1093/infdis/jiac419.

Effectiveness of mRNA Booster Vaccination Against Mild, Moderate, and Severe COVID-19 Caused by the Omicron Variant in a Large, Population-Based, Norwegian Cohort

Ida Laake  1 , Siri N Skodvin  2 , Kristine Blix  1 , Ida Henriette Caspersen  2 , Håkon K Gjessing  2   3 , Lene K Juvet  4 , Per Magnus  2 , Siri Mjaaland  1 , Anna H Robertson  1 , Jostein Starrfelt  5 , Lill Trogstad  1 , Berit Feiring  1
Affiliations

Effectiveness of mRNA Booster Vaccination Against Mild, Moderate, and Severe COVID-19 Caused by the Omicron Variant in a Large, Population-Based, Norwegian Cohort

Ida Laake et al. J Infect Dis. .

Abstract

Background: Understanding how booster vaccination can prevent moderate and severe illness without hospitalization is crucial to evaluate the full advantage of mRNA boosters.

Methods: We followed 85 801 participants (aged 31-81 years) in 2 large population-based cohorts during the Omicron BA.1/2 wave. Information on home testing, PCR testing, and symptoms of coronavirus disease 2019 (COVID-19) was extracted from biweekly questionnaires covering the period 12 January 2022 to 7 April 2022. Vaccination status and data on previous SARS-CoV-2 infection were obtained from national registries. Cox regression was used to estimate the effectiveness of booster vaccination compared to receipt of 2-dose primary series >130 days previously.

Results: The effectiveness of booster vaccination increased with increasing severity of COVID-19 and decreased with time since booster vaccination. The effectiveness against severe COVID-19 was reduced from 80.9% shortly after booster vaccination to 63.4% in the period >90 days after vaccination. There was hardly any effect against mild COVID-19. The effectiveness tended to be lower among subjects aged ≥60 years than those aged <50 years.

Conclusions: This is the first population-based study to evaluate booster effectiveness against self-reported mild, moderate, and severe COVID-19. Our findings contribute valuable information on duration of protection and thus timing of additional booster vaccinations.

Keywords: COVID-19; MoBa; SARS-CoV-2; booster vaccination; disease severity; mRNA vaccine; vaccine effectiveness.

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Conflict of interest statement

Potential conflicts of interests. J. S. has contributed to vaccine effectiveness studies funded by the European Medicines Agency and the European Centre for Disease Prevention and Control. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

Figures

Figure 1.
Figure 1.
Flow chart of the study population. Abbreviations: MoBa, Norwegian Mother, Father, and Child Cohort Study; MSIS, Norwegian Surveillance System for Communicable Disease; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.
Figure 2.
Figure 2.
Relative effectiveness of booster vaccination (third dose) with mRNA vaccine against SARS-CoV-2 infection caused by the Omicron variant compared to a reference group vaccinated with 2 doses. Bars represent 95% confidence intervals of the relative vaccine effectiveness.
See this image and copyright information in PMC

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