Research suggests COVID-19 vaccines may protect against pneumonia

Chest computed tomography demonstrated a lower frequency of pneumonia in fully vaccinated patients compared to unvaccinated patients, with a significantly lower frequency in patients who received the Pfizer vaccine.

Chest computed tomography (CT) scan suggests COVID-19 vaccines protect against pneumoniaaccording to a study published in the American Journal of Radiology.

Among adults who received 2 doses of the Pfizer or AstraZeneca COVID-19 vaccine but had a breakthrough infection, CT scans were less likely to show the frequency and severity of pneumonia, compared to unvaccinated patients.

To arrive at this discovery, the study authors analyzed CT images of 467 patients collected from 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 with symptomatic COVID-19.

In 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 not vaccinated. Booster or supplemental doses were not mentioned in the study.

When analyzing these scans, the authors found a lower frequency of pneumonia in vaccinated patients than in unvaccinated patients. Additionally, the Pfizer mRNA vaccine was associated with a significantly higher freedom from pneumonia compared to the AstraZeneca adenoviral vector vaccine.

The frequency of absence of pneumonia on CT was only 15% in unvaccinated patients. Meanwhile, 51% of patients vaccinated with Pfizer and 29% of patients vaccinated with AstraZeneca had pneumonia-free scans.

“Pre-vaccination allows faster clearance of viral RNA and results in lower viral load, with potential containment of infection in the upper respiratory tract,” the authors said. “This mechanism may explain the present study’s observation of lower frequency and severity of pneumonia in fully vaccinated patients with COVID-19.”

The CT severity score (CT-SS) was also measured, with almost perfect inter-rater agreement between the 3 radiologists included in the study (intra-class correlation coefficient, 0.91; 95% CI, 0. 89-0.92).

Mean CT-SS was significantly higher in unvaccinated patients (9.7 [6.1]) compared to 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 = 0.24).

The authors also noted that the frequency of fever was significantly higher in unvaccinated patients (79%) compared to patients fully vaccinated with Pfizer (43%) or AstraZeneca (54%). Among the vaccinated group, the frequency of dyspnoea or shortness of breath was significantly higher in patients vaccinated with Pfizer (54%) than with AstraZeneca (34%).

The authors found no significant differences when comparing other demographic and clinical characteristics between the groups.

A major limitation of this study was that it was a retrospective, single-center study that included only 2 COVID-19 vaccines. Additionally, the study included only initial CT scans, did not consider other comorbidities or habits that might be additional risk factors, did not include data on viral loads, and did not 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 suggests that the Omicron variant was the dominant variant in this geographic region during the study period, accounting for approximately 80% of COVID-19 diagnoses.


Vicini S, Bellini D, Iannarelli A, et al. Frequency and severity of pneumonia 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

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