This study investigates the immune response in the cancer population in Belgium being vaccinated with an approved vaccine types being authorized for use in Belgium. This question needs to be answered to make sure that this vulnerable population is properly protected against possible SARS-CoV-2 infection and that vaccine administration is safe.

Rationale: Patients with cancer have an increased risk of adverse outcome of COVID-19 and should be at high prioritisation for vaccination against SARS-CoV-2. The COVID-19 vaccine trials have not included cancer patients as such, the efficacy and duration of immunity in patients with cancer are still unknown. Keeping in mind that cancer patients are often immunocompromised, the immune response upon vaccination needs further investigation.

The REAL-V is a prospective, multicenter cohort study. The humoral immunity response based on anti-SARS-CoV-2 IgG antibodies upon COVID-19 vaccination will be investigated in blood samples taken 4 months, 6 months and 12 months after (first) vaccine administration. Potential factors that affect immunity, will be recorded, such as type and stage of cancer, anti-cancer treatment, concomitant medication,..To investigate the safety of different COVID-19 vaccines, incidence and severity of systemic adverse events will be reported using an App based system answering questionnaires about specific vaccine related complaints.

Inclusion Criteria:

• Age of 18 years or older
• Oncological or hematological malignancy or history of it
• Life expectancy > 3 months
• Ability to provide informed consent

Exclusion Criteria:

• Women who are pregnant or breastfeeding
• Immune deficiency not related to cancer or cancer treatment
• Allergy (multiple); to be determined by physician