New Chest CT Study Assesses Impact of COVID-19 Variants and Vaccination Status

Typical computed tomography (CT) findings for COVID-19 are reportedly less likely for people with the omicron variant of the disease in comparison to those with the delta variant, and multiple vaccination dosing reduces the odds of typical CT findings and high CT severity scores in people with COVID-19, according to a newly published multicenter study.

For the retrospective study, recently published in Radiology, researchers in France reviewed CT exams for 3,876 patients (median age of 68) who presented to 93 emergency departments in with COVID-19 between July 2021 and March 2022.

In order to gauge the impact and reflect the peak periods of the omicron and delta variants of COVID-19, the study authors labeled CT exams performed prior to November 15, 2021 as “delta-predominant” (1,080 patients, 28 percent); CT exams performed between November 15 and December 31, 2021 as “transition” (790 patients, 20 percent); and CT exams performed after January 1, 2022 as “omicron-predominant” (1,629 patients, 42 percent).

The study authors found the proportion of typical chest CT findings for COVID-19, ranging from ground glass opacities and consolidations to fibrotic bands and reticulations, was 32 percent higher in non-vaccinated patients (76 percent) in comparison to patients who had at least one vaccination dose (44 percent). Forty-three percent of non-vaccinated patients had a high CT severity score in comparison to 25 percent of vaccinated patients, according to the study.

“Regardless of the period, vaccination was associated with diagnostic and severity scores … with lesser extent of disease and lower frequency of typical patterns in vaccinated patients,” wrote study co-author Guillaume Gorincour, MD, who is affiliated with Imadis Teleradiology in Lyon, France, and colleagues.

(Editor’s note: For related content, see “How Accurate is the CT Severity Score for Predicting COVID-19 Severity?,” “CT Study Reveals Persistent Lung Abnormalities Two Years After COVID-19” and “Study Shows Merits of Photon-Counting CT in Detecting Subtle Post-COVID Lung Abnormalities.”)

The researchers found the proportion of the aforementioned typical chest CT findings for COVID-19, during the omicron-predominant period was 25 percent lower (49 percent) in comparison to the delta-predominant period (74 percent). The proportion of high CT severity scores was 10 percent lower (29 percent) in the omicron-predominant period in comparison to the delta-predominant period (39 percent).

“Radiologists should be aware of the influence of vaccination and novel variants on CT findings and adapt their interpretations and conclusions accordingly, especially since full vaccination coverage is increasing and new omicron subvariants can reinfect previously immunized individuals,” maintained Gorincour and colleagues.

A multivariable analysis found that one vaccine dose was not significantly associated with reduced likelihood of typical chest CT patterns and severity scores in comparison to unvaccinated patients, according to the study. However, Gorincour and colleagues noted that patients with two vaccination doses and three vaccination doses had lower odds ratios (ORs) for typical COVID-19 chest CT findings (32 percent and 20 percent respectively) and high CT severity scores (47 percent and 33 percent respectively) in comparison to unvaccinated patients.

In regard to study limitations, the authors acknowledged possible bias due to subjective assessment of CT severity scores during on-call duty in emergency departments, and knowledge of patient RT-PCR and COVID-19 vaccination status prior to radiologist assessment of chest CTs. Gorincour and colleagues also noted that bronchial wall thickening and peribronchovascular predilection, more commonly reported with the omicron variant, were not assessed in this study.