Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2023 Mar 14;17(3):e13121.
doi: 10.1111/irv.13121. eCollection 2023 Mar.

Comparative complete scheme and booster effectiveness of COVID-19 vaccines in preventing SARS-CoV-2 infections with SARS-CoV-2 Omicron (BA.1) and Delta (B.1.617.2) variants: A case-case study based on electronic health records

Irina Kislaya  1   2   3 , André Peralta-Santos  2   3   4 , Vítor Borges  5 , Luís Vieira  6 , Carlos Sousa  7 , Bibiana Ferreira  8   9 , Ana Pelerito  10 , João Paulo Gomes  5 , Pedro Pinto Leite  4 , Baltazar Nunes  1   2   3 ; PT COVID‐19 group; Ausenda Machado  1   2   3   4   5   6   7   8   9   10 , Ana Paula Rodrigues  1   2   3   4   5   6   7   8   9   10 , Vasco Ricoca Peixoto  1   2   3   4   5   6   7   8   9   10 , Pedro Casaca  1   2   3   4   5   6   7   8   9   10 , Eugenia Fernandes  1   2   3   4   5   6   7   8   9   10 , Eduardo Rodrigues  1   2   3   4   5   6   7   8   9   10 , Rita Ferreira  1   2   3   4   5   6   7   8   9   10 , Joana Isidro  1   2   3   4   5   6   7   8   9   10 , Miguel Pinto  1   2   3   4   5   6   7   8   9   10 , Sílvia Duarte  1   2   3   4   5   6   7   8   9   10 , Daniela Santos  1   2   3   4   5   6   7   8   9   10 , Luís Meneses  1   2   3   4   5   6   7   8   9   10 , José Pedro Almeida  1   2   3   4   5   6   7   8   9   10 , Ana Matias  1   2   3   4   5   6   7   8   9   10 , Samanta Freire  1   2   3   4   5   6   7   8   9   10 , Teresa Grilo  1   2   3   4   5   6   7   8   9   10
Affiliations

Comparative complete scheme and booster effectiveness of COVID-19 vaccines in preventing SARS-CoV-2 infections with SARS-CoV-2 Omicron (BA.1) and Delta (B.1.617.2) variants: A case-case study based on electronic health records

Irina Kislaya et al. Influenza Other Respir Viruses. .

Abstract

Background: Information on vaccine effectiveness in a context of novel variants of concern (VOC) emergence is of key importance to inform public health policies. This study aimed to estimate a measure of comparative vaccine effectiveness between Omicron (BA.1) and Delta (B.1.617.2 and sub-lineages) VOC according to vaccination exposure (primary or booster).

Methods: We developed a case-case study using data on RT-PCR SARS-CoV-2-positive cases notified in Portugal during Weeks 49-51, 2021. To obtain measure of comparative vaccine effectiveness, we compared the odds of vaccination in Omicron cases versus Delta using logistic regression adjusted for age group, sex, region, week of diagnosis, and laboratory of origin.

Results: Higher odds of vaccination were observed in cases infected by Omicron VOC compared with Delta VOC cases for both complete primary vaccination (odds ratio [OR] = 2.1; 95% confidence interval [CI]: 1.8 to 2.4) and booster dose (OR = 5.2; 95% CI: 3.1 to 8.8), equivalent to reduction of vaccine effectiveness from 44.7% and 92.8%, observed against infection with Delta, to -6.0% (95% CI: 29.2% to 12.7%) and 62.7% (95% CI: 35.7% to 77.9%), observed against infection with Omicron, for complete primary vaccination and booster dose, respectively.

Conclusion: Consistent reduction in vaccine-induced protection against infection with Omicron was observed. Complete primary vaccination may not be protective against SARS-CoV-2 infection in regions where Omicron variant is dominant.

Keywords: COVID‐19; Delta variant; Omicron variant; SARS‐CoV‐2; case–case design; vaccine effectiveness.

PubMed Disclaimer

Conflict of interest statement

Dr. Peralta‐Santos reports to participate as a speaker in scientific meetings sponsored by Pfizer. Other authors report no potential conflicts of interest.

Figures

FIGURE 1
FIGURE 1
Participants selection flowchart, Portugal, Weeks 49–51, 2021. (A) Participants aged 12+ years old. (B) Participants aged 50+ years old. SGTF, S‐gene target failure; WGS, whole‐genome sequencing.
See this image and copyright information in PMC

References

    1. Viana R, Moyo S, Amoako DG, et al. Rapid epidemic expansion of the SARS‐CoV‐2 Omicron variant in southern Africa. Nature. 2022;603(7902):679‐686. Available from: https://pubmed.ncbi.nlm.nih.gov/35042229/ - PMC - PubMed
    1. World Health Organization . Classification of Omicron (B.1.1.529): SARS‐CoV‐2 Variant of Concern. Vol. 337, WHO. 2021. [cited 2022 Jan 31]. Available from: https://www.who.int/news/item/26-11-2021-classification-of-omicron-(b.1....
    1. Pulliam JRC, van Schalkwyk C, Govender N, et al. Increased risk of SARS‐CoV‐2 reinfection associated with emergence of the Omicron variant in South Africa. medRxiv. 2021. Dec 2 [cited 2022 Jan 31];2021.11.11.21266068. Available from: https://www.medrxiv.org/content/10.1101/2021.11.11.21266068v2 - DOI - PMC - PubMed
    1. Karim SSA, Karim QA. Omicron SARS‐CoV‐2 variant: a new chapter in the COVID‐19 pandemic. Lancet (London, England). 2021;398(10317):2126‐2128. Available from: https://pubmed.ncbi.nlm.nih.gov/34871545/ - PMC - PubMed
    1. European Centre for Disease Prevention and Control (ECDC) . Methods for the detection and characterisation of SARS‐CoV‐2 variants—first update 20 Dec 2021. 2021.

Publication types

Substances

Supplementary concepts