Comparison of Estimated Relative Risk for Symptomatic Infection of Alpha, Delta, and Omicron Variants of SARS-CoV-2 Following Two-Dose versus Three-Dose (Booster) Vaccine Series
14 Pages Posted: 24 Jan 2022 Last revised: 28 Jan 2022
Date Written: January 27, 2022
Abstract
Previous research indicates that a third (booster) dose of an mRNA vaccine reduces the risk of SARS-CoV-2 infection compared to only a two-dose series of vaccinations. However, this data is centered around the B.1.617.2 (Delta) variant, there is little epidemiologic data regarding the effectiveness of a booster dose to reduce the risk of the B.1.1.529 (Omicron) variant. This study used summary data reported by Christensen et al to estimate the relative risk of symptomatic Omicron and Delta infection between individuals who have received a two- versus three-dose vaccine series. Individuals who only received two doses of vaccine were at a substantially greater risk for Delta infection compared to those who received a booster [relative risk (RR) =10.91; 95 confidence interval = 9.22-12.91, p<0.0001], however, this was not so with Omicron [RR=1.07 (0.98-1.16), p=0.1422]. Unvaccinated individuals (zero or one doze) were at substantially greater risk of all infection with each of the three variants compared to fully vaccinated (two- or three-dose) individuals. These preliminary findings suggest that a booster has clear benefit for reducing the risk of symptomatic Delta variant infection, but is less so for Omicron. These findings are meant to help provide some early data regarding the efficacy reducing risk of a SARS-CoV-2 vaccine booster dose for symptomatic Omicron infection, but must be interpreted within the context of multiple limitations (i.e., relatively small sample size from preliminary data within a single healthcare system, not controlling for age and various other risk factors, numerous assumptions required for epidemiologic analysis).
Note:
Funding: The author of this paper did not receive any funding to perform this research.
Declaration of Interests: No support from any organization for the submitted work; no financial relationships with any organizations that might have an interest in the submitted work; no other relationships or activities that could appear to have influenced the submitted work.
Keywords: COVID19, COVID-19, booster, vaccine, SARS-CoV-2, Omicron
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