key: cord-1032493-vp2t4xkn
authors: Hansen, C. H.; Schelde, A. B.; Moustsen-Helms, I. R.; Emborg, H.-D.; Krause, T. G.; Moelbak, K.; Valentiner-Branth, P.; Institut, The Infectious Disease Preparedness Group at Statens Serum
title: 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
date: 2021-12-21
journal: nan
DOI: 10.1101/2021.12.20.21267966
sha: ece8315a8af71e4914c1c4624f693464e467cbd7
doc_id: 1032493
cord_uid: vp2t4xkn

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 -19 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%).

On 26 November, 2021, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant B.1.1.529, named Omicron, was classified as a variant of concern by the WHO and is currently spreading rapidly across the globe including in Denmark. 1, 2 Here, we estimate COVID-19 vaccine protection against infection with Omicron or Delta up to five months after primary vaccination using Danish nationwide data.

Complete residency, COVID-19 PCR test and vaccination data were extracted from Danish nationwide registries. Nearly all PCR-confirmed COVID-19 cases identified in the country during the study period (November 20 to December 12, 2021) were investigated for Omicron by wholegenome sequencing or a novel variant specific PCR test targeting the 452L mutation. Cases not identified as Omicron were assumed to be Delta.

Vaccine effectiveness (VE) was estimated in a time-to-event analysis of Danish residents VE was calculated as 1-HR with HR (hazard ratio) estimated in a Cox regression model adjusted for age, sex and geographical region, and using calendar time as the underlying time scale. All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 21, 2021. ; https://doi.org/10.1101/2021.12.20.21267966 doi: medRxiv preprint

By December 12, 2021, there were 5,767 identified Omicron cases in Denmark with a median age of 28 years (93% <60 years). Among those who had most recently completed primary vaccination, VE against Omicron was 55.2% (95% confidence interval: 23.5 to 73.7%) and 36.7% (-69.9 to 76.4%) for the BNT162b2 and mRNA-1273 vaccines, respectively, but with evidence of rapid waning over the course of five months. By comparison, VE against Delta was significantly higher and better preserved over the same period (see Figure and Table) . A recent study from England (in preprint) found higher effectiveness against symptomatic Omicron initially after BNT162b2 vaccination followed by a rapid decline in protection, and that VE increased to 75.5% (56.1 to 86.3%) two weeks after booster vaccination using unvaccinated individuals as comparison.

Our study contributes to emerging evidence that BNT162b2 or mRNA-1273 primary vaccine protection against Omicron decreases quickly over time with booster vaccination offering a All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 21, 2021. ; https://doi.org/10.1101/2021.12.20.21267966 doi: medRxiv preprint significant increase in protection. In light of the exponential rise in Omicron cases, these findings highlight the need for massive rollout of vaccinations and booster vaccinations. All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 21, 2021. ; https://doi.org/10.1101/2021.12.20.21267966 doi: medRxiv preprint

SARS-CoV-2 Variant of Concern

Epidemiological characterisation of the first 785 SARS-CoV-2 Omicron variant cases in Denmark

Effectiveness of COVID-19 vaccines against the Omicron (B.1.1.529) variant of concern