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Vaccine effectiveness against SARS-CoV-2 infection with the Omicron or Delta variants following a two-dose or booster BNT162b2 or mRNA-1273 vaccination series: A Danish cohort study
Open accessAbstract
In this brief communication we are showing original research results with early estimates from Danish nationwide databases of vaccine effectiveness (VE) against the novel SARS-CoV-2 Omicron variant (B.1.1.529) up to five months after a primary vaccination series with the BNT162b2 or mRNA-1273 vaccines. Our study provides evidence of protection against infection with the Omicron variant after completion of a primary vaccination series with the BNT162b2 or mRNA-1273 vaccines; in particular, we found a VE against the Omicron variant of 55.2% (95% confidence interval (CI): 23.5 to 73.7%) and 36.7% (95% CI: -69.9 to 76.4%) for the BNT162b2 and mRNA-1273 vaccines, respectively, in the first month after primary vaccination. However, the VE is significantly lower than that against Delta infection and declines rapidly over just a few months. The VE is re-established upon revaccination with the BNT162b2 vaccine (54.6%, 95% CI: 30.4 to 70.4%).
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“As documented in the literature [19,22,26], VE during the Delta-dominant period was higher compared to the Omicron BA.1-dominant period”
From Vaccine effectiveness and duration of protection of COVID-19 mRNA vaccines against Delta and Omicron BA.1 symptomatic and severe COVID-19 outcomes in adults aged 50 years and over in France (2023) · cites this paper as [26]
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“this decrease in protection was substantially higher against Omicron BA.1 compared to Delta [3,8,12,19,26].”
From Vaccine effectiveness and duration of protection of COVID-19 mRNA vaccines against Delta and Omicron BA.1 symptomatic and severe COVID-19 outcomes in adults aged 50 years and over in France (2023) · cites this paper as [26]
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“Several studies have described a drop over time of two-dose vaccine effectiveness against SARS-CoV-2 symptomatic infection;”
From Vaccine effectiveness and duration of protection of COVID-19 mRNA vaccines against Delta and Omicron BA.1 symptomatic and severe COVID-19 outcomes in adults aged 50 years and over in France (2023) · cites this paper as [26]
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“Still, numerous studies conducted during the Omicron BA.1 period have reported an increase in VE against infection caused by this variant following a booster dose [19,26,32-35].”
In the citing paper
“Notwithstanding these limitations, findings were consistent with those of other studies of vaccine effectiveness against omicron infection (BA.1 or BA.2 subvariants were not specified).27,32-36”
From Effects of Previous Infection and Vaccination on Symptomatic Omicron Infections (2022) · cites this paper as [33]
In the citing paper
“Notwithstanding these limitations, consistent findings were reached, indicating rapid waning of vaccine protection against symptomatic Omicron infection that are consistent with findings of other studies for effectiveness against Omicron infection (with no BA.1/BA.2 subvariant specified)42–48.”
From Duration of mRNA vaccine protection against SARS-CoV-2 Omicron BA.1 and BA.2 subvariants in Qatar (2022) · cites this paper as [44]
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Self-citationAnalysis of licensed over-the-counter (OTC) antibiotics in the European Union and Norway, 2012
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Research works printed but not linked: 1
- Andrews N , Stowe J , Kirsebom F , et al. Effectiveness of COVID-19 vaccines against the Omicron (B.1.1.529) variant of concern [Preprint]. https://khub.net/documents/135939561/430986542/Effectiveness+of+COVID-19+vaccines+against+Omicron+variant+of+concern.pdf/f423c9f4-91cb-0274-c8c5-70e8fad50074
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Metadata
- Authors
- Hansen, C. H., Schelde, A. B., Moustsen-Helm, I. R., Emborg, H.-D., Krause, T. G., Mølbak, K., & Valentiner-Branth, P.
- Affiliations
- Statens Serum Institut (DK)
- ORCID
- Venue
- medRxiv
- Publisher
- openRxiv
- Published
- 2021-12-21
- OpenAlex
- W4200175757
- Cited by
- 133
- References
- 1
- Citations by year
- 2026: 2 · 2025: 1 · 2024: 8 · 2023: 25 · 2022: 97
- Type
- posted content
- Language
- en
- Open access
- green
- doi.org
- Locations
- medRxiv (acceptedVersion)
- Topics
- Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
- Physical Sciences › Mathematics › Modeling and Simulation › COVID-19 epidemiological studies
- Social Sciences › Health › Vaccine Coverage and Hesitancy
- Keywords
- vaccine effectiveness, SARS-CoV-2, Omicron variant, Delta variant, BNT162b2, mRNA-1273, COVID-19 vaccines, booster vaccination, waning immunity, Danish cohort
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