Dear editor, we would like to share ideas on the publication “Temporal metabolic response to mRNA COVID-19 vaccinations in oncology patients [1].” Advani et al. concluded that “Consideration should be given to performing FDG PET at least 2 weeks after the COVID-19 vaccine. [1].” This report can confirm that both immunological and metabolic responses occurred at lymph node following COVID-19 mRNA vaccination. Waiting might be a good practice. However, the problem might still exist after 2-week period of waiting and it is sometimes not possible to have a long waiting. To avoid interference in medical imaging for cancerous case, in a recent report, it is recommended for “administering the vaccine in the arm contralateral to a unilateral cancer [2].”