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Introduction In this single-centre retrospective observational study, the 8-week safety and the efficiency of a single dose of BNT162b2 vaccine was studied in 83 HD patients. Methods All clinically stable adult ESRD patients on chronic HD for at least 4 weeks were screened for participation in the study. Exclusion criteria for enrollment in the study included a medical history of COVID-19 infection within the last 12 weeks or delivery of both vaccine doses less than 8 weeks apart from each other. The same patients during the 8-week period that preceded the vaccination served as controls of themselves. The vaccine was administered intramuscularly in the deltoid muscle, on a dialysis day, at least 30 min either pre- or post-dialysis. The primary end-point of the study was severe COVID-19 infection, and/or death due to COVID-19 pneumonitis. Furthermore, all vaccinated patients were scrutinized for any local or systemic reactions within the first 7 days post-vaccination. Results Amongst 113 adult HD patients in our Unit, in total 83 patients had the first 30 μg dose of the BNT162b2 vaccine and were considered eligible to be included in the study. The 8-week survival rate was 91% for the controls and 100% for the vaccine group. No life-threatening allergic reaction or other side-effect was observed post-vaccination. Conclusion The BNT162b2 vaccine can be safely used in HD patients and seems to offer significant protection against the infection even after the first vaccine dose.

Significance The connection between brain and peripheral lymphatics has been studied for 250 y, mainly in animals. Specific markers for lymphatic endothelial cells (LECs) were discovered about a decade ago. We stained postmortem human brains with LYVE1 and PDPN to identify LECs. Marker-positive cells were found in membranes covering the brain, walls of vessels, and perivascular spaces, and among nerve fibers. These spaces also seem to contain T cells and are connected to peripheral lymphatics through passageways in the nasal cavity, optic nerve, and base of the skull. Our findings show a path that brain waste products take when they leave the central nervous system, paths that may be bidirectional., Almost 150 papers about brain lymphatics have been published in the last 150 years. Recently, the information in these papers has been synthesized into a picture of central nervous system (CNS) “glymphatics,” but the fine structure of lymphatic elements in the human brain based on imaging specific markers of lymphatic endothelium has not been described. We used LYVE1 and PDPN antibodies to visualize lymphatic marker-positive cells (LMPCs) in postmortem human brain samples, meninges, cavernous sinus (cavum trigeminale), and cranial nerves and bolstered our findings with a VEGFR3 antibody. LMPCs were present in the perivascular space, the walls of small and large arteries and veins, the media of large vessels along smooth muscle cell membranes, and the vascular adventitia. Lymphatic marker staining was detected in the pia mater, in the arachnoid, in venous sinuses, and among the layers of the dura mater. There were many LMPCs in the perineurium and endoneurium of cranial nerves. Soluble waste may move from the brain parenchyma via perivascular and paravascular routes to the closest subarachnoid space and then travel along the dura mater and/or cranial nerves. Particulate waste products travel along the laminae of the dura mater toward the jugular fossa, lamina cribrosa, and perineurium of the cranial nerves to enter the cervical lymphatics. CD3-positive T cells appear to be in close proximity to LMPCs in perivascular/perineural spaces throughout the brain. Both immunostaining and qPCR confirmed the presence of adhesion molecules in the CNS known to be involved in T cell migration.