Nearly half of omicron patients in Houston hospitals were vaccinated, according to new study

Omicron caused more breakthrough cases than Alpha or Delta in the study.

Updated: January 3, 2022 - 7:50pm

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Nearly half of omicron cases in a Houston hospital system were breakthrough cases, but overall the new COVID variant seems to be less severe according to a not-yet-peer-reviewed study funded in part by the U.S. government.

Researchers studied COVID cases at the Houston Methodist healthcare system and identified 862 people with symptomatic omicron infections from late Nov. to Dec. 18, 2021. The study, published Sunday, reported that early signs show more people are getting infected with omicron despite being vaccinated. Patients with the new variant are "significantly less likely to be hospitalized," and the disease is less severe overall. 

Of the patients with omicron, 430 of them had been vaccinated, and researchers state that compared to patients with other variants, omicron caused "a significantly greater percentage" of breakthrough cases.

Additionally, according to the study, nearly 9.9% of omicron patients had received a COVID booster.

“Consistent with Omicron causing a significantly increased number of vaccine breakthrough cases, it has been reported that this variant has reduced sensitivity to antibody neutralization in vitro, likely in large part due to the extensive number of amino acid and other structural changes occurring in Omicron spike protein,” the researchers wrote.

The study was authored by researchers from the Houston Methodist Research Institute, the University of Chicago the ​​Argonne National Laboratory and other locations. It was funded by the Houston Methodist Academic Institute Infectious Diseases Fund and the National Institute of Allergy and Infectious Diseases, the latter of which is under Dr. Anthony Fauci. 

The researchers state that key findings include the fact that omicron "rapidly increased as a cause of COVID-19 and spread throughout the metroplex in an unusually short period of time, far faster than any other SARS-CoV-2 variant." 

Additionally, they stated that omicron caused more breakthrough cases than Alpha or Delta, and the patients were significantly younger than those with other variants. Compared to Alpha and Delta, "significantly fewer omicron patients required hospitalization," the researchers wrote, adding that when people were hospitalized for the new variant, it was for less time.

Omicron is known to be extremely contagious, and within three weeks caused 90% of all new COVID cases in the study. 

Other studies signal that omicron seems to be less severe than other COVID variants. 

Officials in South Africa said last week that the death toll from the most recent Omicron wave is "extremely low."