Comparison between viral vector and mRNA based COVID-19 vaccination in prevalence and severity of regional immune reactions, and 18F-FDG PET/CT features

Document Type : Original Article


1 Department of Nuclear medicine, ultrasound & PET, Westmead hospital, NSW, Australia

2 Department of Nuclear Medicine, Ultrasound & PET, Westmead hospital, NSW, Australia

3 Nuclear Medicine Research Center, Mashhad University of Medical Sciences


Objective(s): The coronavirus pandemic caused by SARS-CoV-2 commenced in late 
2019, and global wide vaccination appears to be the only reasonable solution to 
fight this dreadful virus. There are two main types of COVID-19 immunization using 
viral vector and mRNA-based vaccines. However, the impact of each of type on 18FFDG PET/CT needs to be accurately assessed. This study aimed to compare the 18FFDG PET/CT features of these two types of COVID-19 vaccines.
Methods: A total of 188 patients referred for 18F-FDG PET/CT with a recent history 
of either BioNTech/Pfizer or AstraZeneca COVID-19 vaccination, and a control 
group of 40 patients with no history of any type of recent vaccination, were 
included in the study. 18F-FDG PET/CT studies of vaccinated patients assessed for 
injection site uptake and regional nodal and systemic reactions post vaccination. 
The data were compared to the control group and to the contralateral side for each 
patient. The findings were compared between patients who received Pfizer and 
AstraZeneca vaccines.
Results: 18F-FDG PET/CT was semiquantitatively positive in 50.5% of the studied 
population for vaccine-related features. The ipsilateral axillary and infra- and 
supraclavicular lymph nodes were significantly larger in size and exhibited higher 
metabolic activity compared to the contralateral lymph nodes after both types of 
vaccination. The prevalence of regional nodal reactions post Pfizer and 
AstraZeneca vaccination was 39% and 17.9% on visual, and 61% and 47.6% on 
semiquantitative assessments, respectively. Patients receiving the Pfizer vaccine 
exhibited higher metabolic activity in the ipsilateral regional lymph nodes 
(p<0.05). No significant difference in the intensity of regional nodal reaction post 
vaccination was noted between the first four weeks.
Conclusion: Significant local and regional nodal reactions are observed after both 
viral vector and mRNA COVID-19 vaccination with a tendency to extend toward the 
infra- and supraclavicular nodal stations but not to the pulmonary hilum. The 
greater intensity and extension of the nodal reaction after Pfizer vaccination 
suggests a higher possibility of false-positive results on 18F-FDG PET/CT studies 
using mRNA vaccination technology.


Main Subjects