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URMC / Highland Hospital / Medical Professionals / Physician News / February 2022 / Delta and Omicron Variants and Vaccine Efficacy

Delta and Omicron Variants and Vaccine Efficacy

The post- holiday season has presented unique challenges for Highland with COVID cases on the rise in both patients and our staff. Many people are wondering about break-through cases and the efficacy of the vaccine. I want to share with you some information as well as some research done by Linda Greene, RN, MPS, CIC, FAPIC, Director of Hospital Infection Prevention.

Although nationally vaccine effectiveness declined during the Omicron-predominant period compared to the Delta-predominant period, two separate studies published by the CDC at the end of January explored vaccine and booster dose effectiveness against the periods in which Delta and Omicron were emerging and predominant. The effectiveness of two mRNA vaccine doses were higher against COVID-19 hospitalizations compared to non-vaccinated individuals. Rates of COVID-19 cases were lowest among fully vaccinated people with a booster dose. 

A recent study in JAMA suggests that among both Omicron and Delta variant cases, Cycle Threshold (Ct) values were generally higher (reflecting less genetic material detected) among those with three vaccine doses compared with unvaccinated or those with two doses. Although there is evidence that hospitalizations are less frequent in boosted individuals, this may also suggest that potential for transmission is also lessened.

Here at Highland Hospital, new cases of COVID-19 were tracked and analyzed from June 27, 2021, through the present, and were consistent with the initial Delta surge and more recently, the Omicron surge. As of January 24, unvaccinated individuals continue to make up more than 60% of our cases and are typically younger individuals without comorbidities. Although the rate of hospitalization of vaccinated cases has risen slightly with the Omicron variant, 86% of those individuals have comorbidities and 65% are over 65 years of age. Of the vaccinated admissions, 17% have received a booster. Many of these patients have milder disease. Since October, 2021, ICU admissions in unvaccinated individuals are 8.6% compared to 4.5% in the vaccinated group. 

2/3/2022

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