Effects of COVID-19 vaccination on cervical lymph nodes in patients with thyroid cancer.

Background: Cervical lymph node enlargement caused by coronavirus disease 2019 (COVID-19) vaccination has been reported, but little is known on whether the vaccination would influence preoperative cervical lymph node evaluation and its risk of lymph node metastasis in thyroid cancer.

Methods: We retrospectively analyzed data of patients who underwent thyroid cancer surgery in Tangdu Hospital, China, from 1 March 2021 to 30 June 2021. A total of 182 patients were included in the cohort study. All patients with suspected malignant tumors underwent ultrasound (US)-guided fine needle aspiration (FNA) of thyroid lesions before surgery to confirm the diagnosis. Cervical lymph nodes were evaluated by preoperative physical examination and imaging. Wilcoxon rank-sum test and Fisher's exact test were used to evaluate the effect of vaccination on cervical lymph nodes in patients with thyroid cancer. Statistical significance was defined at P<0.05.

Results: The patients were divided into two groups according to whether they had been vaccinated or not. Our results showed that there were no significant differences between the two groups in the brand of the vaccine, operation method, and the extent of surgery. Moreover, there was no significant difference in the evaluation of US characteristics of cervical lymph nodes between the two groups regardless of having the vaccination or not. Interestingly, US evaluation found that the experimental group's proportion of cervical lymph node enlargement increased significantly within 14 days after vaccination, which was statistically significant.

Conclusions: This study found that vaccination against COVID-19 did not increase the number of cervical lymph node metastases, but inaccurate assessment of cervical lymph nodes in thyroid cancer patients within 14 days of vaccination (due to temporary lymph node enlargement) may lead to more extensive surgery.