Impact of Vaccination and the Omicron Variant on COVID-19–related Chest CT Findings: A Multicenter Study

Abstract

Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) omicron variant has a higher infection rate than previous variants but results in less severe disease. However, the impacts of omicron and vaccination on chest CT findings are difficult to evaluate. Purpose To investigate the impact of vaccination status and predominant variant on chest CT findings, diagnostic and severity scores in multicenter sample of consecutive patients referred to emergency departments for proven COVID-19. Materials and Methods This retrospective, multicenter study included adults referred to 93 emergency departments with SARS-CoV-2 infection according to RT-PCR and known vaccination status between July 2021 and March 2022. Clinical data and structured chest CT reports including semiquantitative diagnostic and severity scores following the French Society of Radiology-Thoracic Imaging Society guidelines were extracted from a teleradiology database. Observations were divided into ‘delta-predominant’, ‘transition’, and ‘omicron-predominant’ periods. Associations between scores and variant and vaccination status were investigated with Chi-square tests and ordinal regressions. Multivariable analyses evaluated the influence of omicron variant and vaccination status on the diagnostic and severity scores. Results Overall, 3876 patients were included (median age: 68 years [Q1-Q3: 54-80], 1695 females). Diagnostic and severity scores were associated with the predominant variant (delta- versus omicron-predominant, Chi-square=112.4 and 33.7, both P <.001) and vaccination (Chi-square=243.6 and 210, both P <.001) and their interaction (Chi-square=4.3, P =.04 and Chi-square=28.7, P <.001, respectively). In multivariable analyses, omicron variant was associated with lower odds of typical CT findings than delta variant (OR=0.46, P <.001). Two and three vaccine doses were associated with lower odds of demonstrating typical CT findings (OR=0.32 and OR=0.20, both P <.001), and of having high severity score (OR=0.47 and OR=0.33, both P <.001), compared with unvaccinated patients. Conclusion Both the omicron variant and vaccination were associated with less typical chest CT manifestations for COVID-19 and lesser extent of disease. See also the editorial by Yoon and Goo in this issue.

Changes in COVID-19 CT Manifestations with Vaccination and the Omicron Variant

“…The study provided more robust evidence on the independent associations of vaccination and Omicron with the CT manifestations of COVID-19 ( 8 ). Omicron has been found to replicate more efficiently in the bronchi than in the lung parenchyma compared with other variants ( 6 ), and vaccination enhances immunity, inhibiting viral replication.…”

“…While vaccine effectiveness against SARS-CoV-2 infection decreases over time (from 83% in the first month to 22% at 5 months or longer for all infections; from 94% to 64% for symptomatic infections), vaccine effectiveness against severe infection remains well-maintained, at around 90%, at 5 months or longer ( 9 ). In line with the prolonged effectiveness against severe infections, Crombé et al found that the proportions of patients with no pneumonia, typical CT findings, and severe pneumonia involving at least 25% of the lung parenchyma remained stable regardless of the interval between vaccination and infection (up to 6 months or longer) ( 8 ). This may imply that vaccine effectiveness against pneumonia resembles the protection from severe infections, rather than the protection from all infections, and may wane to a lesser extent than against SARS-CoV-2 infection itself.…”

“…In this issue of Radiology , Crombé et al ( 8 ) prospectively assessed the real-world impact of vaccination and the Omicron variant together on chest CT findings and severity scores in a multi-center cohort. The study included 3876 adult patients with SARS-CoV-2 infection from 93 emergency departments in France between July 2021 and March 2022.…”

“…In a subgroup analysis of patients who received at least one vaccine dose, Crombé et al ( 8 ) found that attenuated virus vaccines showed lower effectiveness than mRNA vaccines for preventing pneumonia (22% vs 38%; P =0.03). However, vaccines were still beneficial for patients aged 60 years or older, and the effectiveness of two and three vaccine doses against severe CT pneumonia (pneumonia extent >25%) was similar between the older population (ORs, 0.49 and 0.35, respectively) and the overall study population (ORs, 0.47 and 0.33, respectively).…”

Emergency department CT examinations demonstrate no evidence of early viral circulation at the start of the COVID-19 pandemic—a multicentre epidemiological study

“…Coronavirus disease 2019 (COVID-19) has become endemic worldwide. Latest radiological researches on COVID-19 have shown that the omicron strain and especially the newer omicron variant (BA.5) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) led to higher rates of transmission and decreased severity of infection, subsequently acting as an endemic viral infection [ 1 – 3 ]. To better anticipate the next pandemic, health agencies investigated the first weeks of the COVID-19 outbreak.…”