Chest computed tomography scans demonstrated a lower frequency of pneumonia in fully vaccinated patients compared with unvaccinated patients, with a significantly lower frequency among patients who received the Pfizer vaccine.
Among adults who received 2 doses of either the Pfizer or AstraZeneca COVID-19 vaccine but had a breakthrough infection, CT scans were less likely to show pneumonia frequency and severity, compared with patients who were unvaccinated.
To come to this finding, the study authors analyzed CT images of 467 patients collected at the University of Rome. The mean (SD) age was 65 (17) years, and the group consisted of 250 men and 217 women. All CT scans were performed between December 15, 2021 and February 18, 2022 while the patients were hospitalized for symptomatic COVID-19.
Of this group, 167 patients were fully vaccinated with the Pfizer vaccine and 84 were fully vaccinated with the AstraZeneca vaccine, with full vaccination defined as at least 14 days after receiving the second dose. The remaining 216 patients were unvaccinated. Booster or additional doses were not mentioned in the study.
When analyzing these scans, the authors found a lower frequency of pneumonia in vaccinated patients than unvaccinated patients. Even further, the Pfizer mRNA vaccine was associated with a significantly higher absence of pneumonia compared with the AstraZeneca adenovirus vector vaccine.
Frequency of absence of pneumonia in the CT scans was only 15% in unvaccinated patients. Meanwhile, 51% of patients vaccinated with Pfizer and 29% of patients vaccinated with AstraZeneca had scans absent of pneumonia.
“Prior vaccination enables more rapid clearance of viral RNA and results in a lower viral load, with potential confinement of infection to the upper respiratory tract,” the authors said. “This mechanism may account for the present study’s observation of lower frequency and severity of pneumonia in fully vaccinated patients with COVID-19.”
CT severity score (CT-SS) was also measured, with a nearly perfect inter-rater agreement among the 3 radiologists included in the study (intra-class correlation coefficient, 0.91; 95% CI, 0.89-0.92).
The mean CT-SS was significantly higher among unvaccinated patients (9.7 [6.1]) compared with patients who received the Pfizer (5.2 [6.1]) or AstraZeneca (6.2 [5.9]) vaccine. However, no significant difference was noted between the 2 vaccines (P = .24).
The authors also noted that frequency of fever was significantly higher in unvaccinated patients (79%) compared with patients fully vaccinated with Pfizer (43%) or AstraZeneca (54%). Among the vaccinated group, the frequency of dyspnea or shortness of breath was significantly greater in patients vaccinated with Pfizer (54%) than AstraZeneca (34%).
The authors found no significant differences when comparing other demographic and clinical characteristics among groups.
A major limitation of this study was that it was a single-center retrospective study that only included 2 COVID-19 vaccines. Additionally, the study only included initial CT scans, did not take into account other comorbidities or habits that could pose as additional risk factors, did not include data on viral loads, and did not include data on the type of COVID-19 variant that caused the infection.
However, the authors noted that surveillance data from the National Institutes of Health suggest the Omicron variant was the dominant variant in that geographic region during the study period, accounting for approximately 80% of COVID-19 diagnoses.
Vicini S, Bellini D, Iannarelli A, et al. Pneumonia frequency and severity in patients with symptomatic covid-19: impact of mRNA and adenovirus vector vaccines. AJR Am J Roentgenol. Published online June 1, 2022. doi:10.2214/AJR.22.27843