COVID-19 mRNA Vaccination: Age and Immune Status and Its Association with Axillary Lymph Node PET/CT Uptake

Abstract

With hundreds of millions of coronavirus disease 2019 (COVID-19) messenger RNA (mRNA)-based vaccine doses planned to be delivered worldwide in the upcoming months, it is important to recognize PET/CT findings in recently vaccinated immunocompetent or immunocompromised patients. We aimed to assess PET/CT uptake in the deltoid muscle and axillary lymph nodes of patients who received a COVID-19 mRNA-based vaccine and to evaluate its association with patient age and immune status. Methods: All consecutive adults who underwent PET/CT scans with any radiotracer at our center during the first month of a national COVID-19 vaccination rollout (between December 23, 2020, and January 27, 2021) and had received the vaccination were included. Data on clinical status, laterality, and time from vaccination were prospectively collected, retrospectively analyzed, and correlated with deltoid muscle and axillary lymph node uptake. Results: Of 426 eligible subjects (median age, 67 ± 12 y; 49% female), 377 (88%) underwent PET/CT with ¹⁸F-FDG, and positive axillary lymph node uptake was seen in 45% of them. Multivariate logistic regression analysis revealed a strong inverse association between positive ¹⁸F-FDG uptake in ipsilateral lymph nodes and patient age (odds ratio [OR], 0.57; 95% CI, 0.45-0.72; P < 0.001), immunosuppressive treatment (OR, 0.37; 95% CI, 0.20-0.64; P = 0.003), and presence of hematologic disease (OR, 0.44; 95% CI, 0.24-0.8; P = 0.021). No such association was found for deltoid muscle uptake. The number of days from the last vaccination and the number of vaccine doses were also significantly associated with increased odds of positive lymph node uptake. Conclusion: After mRNA-based COVID-19 vaccination, a high proportion of patients showed ipsilateral lymph node axillary uptake, which was more common in immunocompetent patients. This information will help with the recognition of PET/CT pitfalls and may hint about the patient's immune response to the vaccine.

Keywords: COVID-19; PET/CT; axillary lymphadenopathy; immunogenicity; mRNA vaccine.

Graphical abstract

FIGURE 1.

Patient flowchart.

FIGURE 2.

¹⁸F-FDG PET/CT after COVID-19 vaccination in 66-y-old woman with suspected colon cancer and elevated carcinoembryonic antigen, with no current immunosuppressive treatment: maximal-intensity projection (A), axial multiplanar reformation (B), contrast-enhanced CT (C), and PET/CT (D) 25 d after first vaccine dose and 2 d after second vaccine dose, both in left arm. Increased uptake was observed in left deltoid muscle (arrowhead), corresponding to injection site, and in ipsilateral enlarged axillary lymph nodes (arrows). Otherwise, there were no hypermetabolic findings suggestive of malignancy.

FIGURE 3.

⁶⁸Ga-DOTATATE PET/CT after COVID-19 vaccination in 68-y-old woman with newly diagnosed typical carcinoid (G2), not currently receiving immunosuppressive treatment: maximal-intensity projection (A), axial multiplanar reformation (B), contrast-enhanced CT (C), and PET/CT (D) 24 d after first vaccine and 3 d after second vaccine, both on left side. Increased uptake was observed in left deltoid muscle (arrowhead), corresponding to injection site, and in left axillary lymph nodes of normal size (arrows).

FIGURE 4.

Pathology of reactive, ¹⁸F-FDG–avid, axillary lymph node after COVID-19 vaccination in 41-y-old woman with newly diagnosed left-sided estrogen receptor–positive, progesterone receptor–positive, human epidermal growth factor receptor 2–positive breast cancer: maximal-intensity projection showing marked increase in ¹⁸F-FDG uptake in right deltoid muscle (arrowhead), corresponding to recent second vaccine dose site, and in several left and right axillary lymph nodes (A); axial multiplanar reformation (B); contrast-enhanced CT (C); and PET/CT showing marked bilateral increase in ¹⁸F-FDG uptake in axillary lymph nodes (arrows) (D). First vaccine dose was in left deltoid muscle before diagnosis of breast cancer and 22 d before scan. Second vaccine dose was in right deltoid muscle after diagnosis and 1 d before scan. Patient underwent ultrasound-guided core-needle biopsy to left suggestive axillary lymph node 1 d after PET/CT scan. (E) Hematoxylin- and eosin-stained images of cores of lymph node tissue showing prominently dilated and edematous sinuses that probably reflect reactive changes. Lymphoid tissue is unremarkable, and there is no evidence of malignancy.