Exploring hematic crasis variations in cancer patients following SARS-CoV-2 vaccination: a real-practice study.

SARS-CoV-2 vaccination is strongly recommended, particularly for fragile patients such as those undergoing active oncological treatments. It is crucial to conduct post-marketing surveillance in this patient population. In our study, we conducted a retrospective analysis of real-world data, including 136 patients who received SARS-CoV-2 vaccines and were undergoing anticancer treatments between March 1st and June 30th, 2021. All patients received mRNA vaccines, namely Pfizer-BioNTech's COMIRNATY (BNT162b2 mRNA) and Moderna's mRNA-1273 COVID-19 vaccines. We collected blood samples from the patients one week to 10 days before and after vaccine administration to assess full blood count with white cell differentials. Additionally, we monitored serology titers to detect any previous SARS-CoV-2 infection before hospital admission and tracked changes over time. Our findings revealed a significant occurrence of leukopenia following both the first and second vaccine doses among patients receiving chemotherapy and chemo-immunotherapy. Importantly, this effect was independent of demographic factors such as sex, age, and Body Mass Index. In the chemo-immunotherapy treated group, we observed that concomitant immune-mediated diseases were significantly associated with leukopenia following the second vaccine dose. Notably, in healthy subjects, transient neutropenia was recognized as an adverse event following vaccination. The observed lymphocytopenia during SARS-CoV-2 infection, combined with the impact on leukocyte counts observed in our study, underscores the need for larger post-marketing surveillance studies. Despite a treatment delay occurring in 6.6% of patients, the administration of mRNA vaccines did not have a significant impact on the treatment schedule in our series. These findings from a real-world setting provide valuable insights and suggest avenues for further prospective studies to explore potential complex interactions specific to this patient population.