Observation of the Immune Response After COVID-19 Additional Vaccine Doses in Chronic Patients in Hemodialysis Therapy

Inclusion Criteria: * Informed consent signed and dated by study patient and investigator/authorized physician * Minimum age of 18 years * Ability to understand the nature and requirements of the study * ESKD patients on maintenance hemodialysis with a minimum of 4hrs three times a week at the time of recruitment and a dialysis vintage ≥3 months in NC clinics * Patients that already received three doses against COVID-19 as detailed in the manufacturer's instructions * Patients that are scheduled to receive a fourth vaccine dose of either Comirnaty (BioNTech/Pfizer) or Spikevax (Moderna) after approval of respective national authority. Exclusion Criteria: * Any conditions which could interfere with the patient's ability to comply with the study * Participation in an interventional clinical study during the preceding 30 days * Previous participation in the same study * Patients with proven current COVID-19 infection as identified by routine clinical practice * Patient in therapy with immunosuppressive medications / immunomodulators * Patients who already received a fourth COVID-19 vaccination dose