The population as defined by the inclusion/exclusion criteria and the study logistics were leading to a poor recruitment over the past years.

This trial aims to measure the humoral and adaptive immune response in patients with cancer diagnosis undergoing mRNA vaccination against SARS-CoV-2 and assess its efficacy in preventing COVID-19.

Inclusion Criteria:

1. Age ≥ 18 years old

2. ECOG performance status ≤ 2

3. Subjects with histologically or cytologically confirmed cancer diagnosis (invasive solid tumour or haematological malignancy)

   • undergoing active systemic cancer treatment at the time of the last dose (before ICF signature) of the anti-SARS-CoV-2 mRNA vaccine (such as chemotherapy, immunotherapy, targeted agents, endocrine therapy) in non-metastatic/curative setting or in metastatic/palliative setting
   • or undergoing follow-up after confirmed cancer complete remission without active cancer treatment for the last 12 months at the time of the last dose (before ICF signature ) of the anti-SARS-CoV-2 mRNA vaccine.

4. Life expectancy > 6 months

5. Subjects who received at least 2 doses of mRNA platform vaccination against SARS-CoV-2 as per local guidelines, with the last dose being given between 3 and 12 months prior to baseline assessment.

6. Urine/serum pregnancy test negative for all female subjects of childbearing potential within 7 days prior to subject enrolment.

7. Signed Informed Consent form (ICF) obtained prior to any study related procedure

8. Subject is willing and able to comply with the protocol for the duration of the study including treatment and scheduled visits and examinations.

Exclusion Criteria:

1. Known pregnant and/or lactating women.
2. Subject with a significant medical, neuro-psychiatric, or surgical condition, currently uncontrolled by treatment, which, in the principal investigator's opinion, may interfere with completion of the study.
3. Subjects with active diagnosis of acute leukaemia.
4. Subjects treated with bone marrow transplant < 90 days before received vaccination against SARS-CoV-2.
5. Subjects with a known history of HIV infection.
6. COVID-19 infection in the last 28 days prior to subject enrolment.
7. Subjects receiving prolonged and/or high doses of systemic immunosuppressive therapies including corticosteroids during the last 28 days before receiving first dose of vaccination against SARS-CoV-2 and up to subject enrolment.
8. Subjects who, for any reason, did not receive the 2nd dose of the anti-SARS-CoV-2 mRNA vaccine.
9. Subjects that received the 3rd dose of anti-SARS-CoV-2 mRNA vaccine prior to study entry. Exclusion criterion number 9 is only applicable for previous versions of the protocol and is not applicable from protocol version 3.0 and subsequent versions.
10. Subject that received any dose of non-mRNA anti-SARS-CoV-2 vaccine platform.
11. Subject with a known or suspected history of severe adverse reactions associated with a vaccine and/or with severe allergic reaction to vaccine components or anaphylaxis in the past.
12. Subjects who planned to receive any other licensed vaccines for other indications within 28 days prior to the first booster dose after ICF signature or who are planning to receive any other vaccine up to 14 days after the first booster dose of the mRNA anti-SARS-CoV-2 vaccine after ICF signature (28 days for live attenuated vaccines). For influenza vaccination, a shorter interval or simultaneous administration is acceptable.
13. Subjects who have planned to receive a booster dose after ICF signature but before the baseline assessment
14. Subjects who received COVID-19 pre-exposure prophylactic monoclonal antibodies or who have been treated with anti-SARS-CoV-2 monoclonal antibodies or COVID-19 convalescent plasma during the last 6 months before ICF signature.