We aimed to predict the presence of vaccine-induced hypermetabolic lymph nodes (v-HLNs) on ¹⁸F-FDG PET/CT after coronavirus disease 2019 (COVID-19) vaccination and determine their association with lymphocyte counts. Methods: In this retrospective single-center study, we included consecutive patients who underwent ¹⁸F-FDG PET/CT imaging after messenger RNA– or viral vector–based COVID-19 vaccination between early March and late April 2021. Demographics, clinical parameters, and absolute lymphocyte count (ALC) were collected, and their association with the presence of v-HLNs in the draining territory was studied by logistic regression. Results: In total, 260 patients were eligible, including 209 (80%) women and 145 (56%) with breast cancer. The median age was 50 y (range, 23–96 y). The messenger RNA vaccine had been given to 233 (90%). Ninety (35%) patients had v-HLNs, with a median SUV_max of 3.7 (range, 2.0–26.3), and 74 (44%) displayed lymphopenia, with a median ALC of 1.4 x 10⁹/L (range, 0.3–18.3 x 10⁹/L). An age of no more than 50 y (odds ratio [OR], 2.2; 95% CI, 1.0–4.5), the absence of lymphopenia (OR, 2.2; 95% CI, 1.1–4.3), and less than a 30-d interval from the last vaccine injection to the ¹⁸F-FDG PET/CT (OR, 2.6; 95% CI, 1.3–5.6) were independent factors for v-HLNs on multivariate analysis. In breast cancer patients, the absence of lymphopenia was the only independent factor significantly associated with v-HLNs (OR, 2.9; 95% CI, 1.2–7.4). Conclusion: Patients with a normal ALC after COVID-19 vaccination were more likely to have v-HLNs on ¹⁸F-FDG PET/CT, both of which might be associated with a stronger immune response to vaccination.

^{我们旨在预测 2019 年冠状病毒病 (COVID-19) 疫苗接种后18} F-FDG PET/CT上疫苗诱导的高代谢淋巴结 (v-HLN) 的存在，并确定它们与淋巴细胞计数的关联。方法：在这项回顾性单中心研究中，我们纳入了2021 年 3 月上旬至 4 月下旬在信使 RNA 或基于病毒载体的 COVID-19 疫苗接种后接受¹⁸ F-FDG PET/CT 成像的连续患者。人口统计学、临床参数、收集和绝对淋巴细胞计数 (ALC)，并通过逻辑回归研究它们与引流区域中 v-HLN 存在的关联。结果：总共有 260 名患者符合条件，包括 209 名 (80%) 女性和 145 名 (56%) 乳腺癌患者。中位年龄为 50 岁（范围，23-96 岁）。233 (90%) 人接种了信使 RNA 疫苗。90 名 (35%) 患者患有 v-HLN，中位 SUV_最大值为 3.7（范围，2.0-26.3），74 名（44%）患者出现淋巴细胞减少，中位 ALC 为 1.4 x 10 ⁹ /L（范围，0.3 –18.3 x 10 ⁹ /L）。年龄不超过 50 岁（优势比 [OR]，2.2；95% CI，1.0-4.5），没有淋巴细胞减少症（OR，2.2；95% CI，1.1-4.3），并且小于 30- d 从最后一次疫苗注射到¹⁸F-FDG PET/CT (OR, 2.6; 95% CI, 1.3–5.6) 是多变量分析中 v-HLN 的独立因素。在乳腺癌患者中，没有淋巴细胞减少是与 v-HLN 显着相关的唯一独立因素（OR，2.9；95% CI，1.2-7.4）。结论：接种 COVID-19 后 ALC 正常的患者在¹⁸ F-FDG PET/CT 上更可能出现 v-HLN，这两者都可能与对疫苗接种的更强免疫反应有关。