Dynamic impacts of COVID-19 on immune cells and inflammatory indicators in Chinese medical health workers: a retrospective longitudinal study

Background: The outbreak and ongoing impact of coronavirus disease 2019 (COVID-19) have significantly affected people's physical and mental health, particularly among medical health workers. However, the effects of COVID-19 on the immunity of this population remain unclear. Methods: This retrospective longitudinal study analyzed data from blood routine examinations of medical health workers conducted in 2019, 2020, 2022, and 2024. Data were collected from 1,818 participants, with subgroup analyses stratified by gender. Results: White blood cell (WBC), lymphocyte (LYM), and eosinophil (EOS) counts increased significantly in the post-COVID-19 year compared with the pre-COVID-19 year. Neutrophil (NEUT) counts decreased in COVID-19 year 1 and COVID-19 year 3 but returned to pre-COVID-19 year levels in the post-COVID-19 year. Monocyte (MONO) counts and monocyte-to-lymphocyte ratio (MLR) decreased in COVID-19 year 1, increased to pre-COVID-19 year levels in COVID-19 year 3, and reached their highest levels in the post-COVID-19 year. Basophil (BASO) counts and hemoglobin-to-red blood cell distribution width ratio (HRR) were significantly higher in COVID-19 year 1, COVID-19 year 3, and post-COVID-19 year than in pre-COVID-19 year. Platelet-to-lymphocyte ratio (PLR) in pre-COVID-19 year was significantly higher than in COVID-19 year 1 and post-COVID-19 year, but not significantly different from COVID-19 year 3. Neutrophil-to-lymphocyte ratio (NLR) significantly decreased in post-COVID-19 year when compared with pre-COVID-19 year. Aggregate index of systemic inflammation (AISI) in pre-COVID-19 year was significantly higher than in COVID-19 year 1 and COVID-19 year 3, but significantly lower than in post-COVID-19 year. Systemic inflammation response index (SIRI) decreased in COVID-19 year 1, but up to their pre-COVID-19 year levels in COVID-19 year 3 and post-COVID-19 year. Stratified analysis showed that the impacts of COVID-19 on immune cells and inflammation indicators were more pronounced in female. Conclusion: Immune cells and inflammatory markers in medical health workers underwent changes between 2019 and 2024, particularly among female. Increased attention should be paid to the immune function and mental health of medical health workers.