Inclusion Criteria:  Signed and dated EC-approved informed consent Hematological disease defined according to World Health Organization (WHO) criteria Female or male, 18 years of age or older ECOG performance status 0-3 Willingness and ability to comply with routine clinical practice and study procedures Regular vaccination against SARS-CoV-2 according to Italian Haematological Society (SIE) guidelines/recommendations (Version 2.0, 20 April, 2021). Routine blood test planned between 30 and 60 days after administration of the second vaccine dose according to regular hematological follow up. Routine blood test planned no later than 9 months after the completion of the vaccination series (only in case of absence of circulation specific antibodies).  Exclusion Criteria:  Preventive vaccination against SARS-CoV-2 not administered according to Italian Haematological Society (SIE) guidelines/recommendations (Version 2.0, 20 April, 2021) Evidence of previous infection with the SARS-Cov-2 virus. Routine blood test not planned between 30 and 60 days after administration of the second vaccine dose. Routine blood test not planned within 9 months after the completion of the vaccination series (only in case of absence of circulation specific antibodies).