Duration of ¹⁸F-FDG avidity in lymph nodes after pandemic H1N1v and seasonal influenza vaccination

The aim of our study was to investigate the occurrence of fluorodeoxyglucose (FDG) avidity in draining axillary lymph nodes after vaccination against influenza (H1N1v pandemic and seasonal) and to determine the period of increased FDG uptake.

During December 2009, patients referred for ¹⁸F-FDG positron emission tomography (PET)/CT scans (n = 293) filled in a questionnaire concerning vaccination type (seasonal and/or H1N1v), time and anatomical localization of vaccination. Only injections in deltoid regions were evaluated, thus ensuring that draining lymph nodes were axillary. If more vaccinations had been given, only the latest vaccination was evaluated in each deltoid region.

Of all patients who underwent PET/CT scans during December 2009, 26% had been vaccinated with at least one influenza vaccination in the deltoid region. A total of 92 ‘draining’ and 60 ‘reference’ (i.e. contralateral, non-vaccinated) axillary lymph nodes were evaluated in 61 patients (19 of 61 patients were scanned twice). The maximal intensity in FDG uptake (SUV_max) in draining lymph nodes was 5 g/ml body weight (BW), whereas the maximal intensity in reference lymph nodes was 1.9 g/ml BW. The SUV_max was normalized approximately 40 days after vaccination. No significant enlargement of metabolically active draining lymph nodes could be demonstrated on CT scan. Chemotherapy or immunosuppressive drugs given within 2 weeks from vaccination did not affect SUV_max in the axillary lymph nodes.

Influenza vaccination may lead to FDG-avid draining lymph nodes beyond 1 month.