The Time Course of Serum Iron and Serum Ferritin Concentrations Post-COVID-19 and Influenza Vaccinations

Temporal responses of serum iron and ferritin in COVID-19 infection and vaccination remain insufficiently characterized. This case report presents their timeline after SARS-CoV-2 and influenza vaccinations and may serve as a model for future studies. The approach can be extended to cohort studies or investigations of other acute-phase reactants. A vaccination protocol with a defined timeline can provide a template for COVID-19 and long COVID studies.

Blood samples were collected from vaccination through 6 weeks postvaccination, focusing on iron metabolism. Prevaccination values served as baseline controls. SARS-CoV-2 mRNA vaccination was administered together with routine seasonal influenza vaccination. Previous influenza vaccinations in this patient were not associated with systemic symptoms such as dizziness or fever; in contrast, the present case exhibited clear reactions, suggesting that the observed alterations in serum iron and ferritin are attributable to the SARS-CoV-2 vaccine. The vaccination induced an abrupt decrease in serum iron and a concomitant increase in ferritin. While ferritin returned to baseline within 6 weeks, iron levels steadily increased to approximately 1.8-fold above baseline values but remaining within the reference interval.

The observed decrease in serum iron reflects an iron-withholding response, a well-established host defense mechanism during infections that limits pathogen proliferation. The increase in ferritin requires further interpretation. A hypothesis is presented, but further data are needed to support this mechanism. In future cohort studies, the protocol should include individual prevaccination values so that an additional control group is not necessary.

Immune reactions to vaccines can trigger transient changes in serum iron and ferritin that resemble the acute-phase response observed during infections. This case may serve as a template for studying the kinetics of immune responses, where t = 0 is defined by the vaccination time and each patient serves as own control when prior data are available.