Effectiveness of COVID-19 vaccines against Omicron or Delta in | Mechanical Engineer

Effectiveness of COVID-19 vaccines against Omicron or Delta infection medRxiv Jan 1, 2022 doi: https://doi.org/10.1101/2021.12.30.21268565

Methods Applying the test-negative design to linked provincial data, we estimated vaccine effectiveness against infection (irrespective of symptoms or severity) caused by Omicron or Delta between November 22 and December 19, 2021. We included individuals who had received at least 2 COVID-19 vaccine doses (with at least 1 mRNA vaccine dose for the primary series) and used multivariable logistic regression to estimate the effectiveness of two or three doses by time since the latest dose.

(The study included 3,442 Omicron-positive cases, 9,201 Delta-positive cases, and 471,545 test-negative controls).

HIGHLIGHTS:

- In contrast, receipt of 2 doses of COVID-19 vaccines was not protective against Omicron.

- Vaccine effectiveness against Omicron was 37% (95%CI, 19-50%) ≥7 days after receiving an mRNA vaccine for the third dose.