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The SARS-CoV-2 omicron variant emerged in November 2021 and consists of several mutations within the spike. We used serum from mRNA vaccinated individuals to measure neutralization activity against omicron in a live-virus assay. Following 2-4 weeks after primary series of vaccinations, we observed a 30-fold reduction in neutralizing activity against Omicron. Six months after the initial two vaccine doses, sera from naïve vaccinated subjects showed no neutralizing activity against omicron. In contrast, COVID-19 recovered individuals six months after receiving the primary series of vaccinations show a 22-fold reduction with majority of the subjects retaining neutralizing antibody responses. In naïve individuals following a booster shot (3rd dose), we observed a 14-fold reduction in neutralizing activity against omicron and over 90% of subjects show neutralizing activity. These findings show that a 3rd dose is required to provide robust neutralizing antibody responses against the omicron variant.

Our data suggest that, in hospitals with endemic VRE or continued VRE transmission despite implementation of contact isolation measures, establishing a VRE cohort ward may be a practical and effective method to improve compliance with infection control measures and thereby to control epidemic or endemic VRE transmission.

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