Infection by the recent Coronavirus (SARS-CoV-2) has generated at a pandemic level a new pathology, called COVID-19, characterized by "flu-like" symptoms up to severe acute respiratory failure. The pathogenesis of the disease involves both humoral and cellular immunological responses; cell-mediated immunity is the first and most effective immune response to viral infection. To date, despite the extensive scientific research aimed at curing COVID-19, there are few effective means to tackle SARS-CoV-2 infection and reduce its disease progression. Among these, a first complete anti-SARS-CoV-2 vaccination course has been shown to significantly reduce the development of the disease towards the more severe forms requiring hospital and intensive care. On the other hand, over time the antibody response induced by vaccines against SARS-CoV-2 decreases, so much so as to indicate the need for a third booster dose. This translates into the fact that some patients who have undergone a complete first vaccination course, with third dose booster indications, develop severe critical disease, with the need for hospitalization. On the other hand, other patients with the same vaccination status do not develop the disease, although they are also positive for SARS-CoV-2. The investigators therefore hypothesized that the humoral and cell-mediated response among groups of patients may be radically different. For these reasons, the investigators designed this observational pilot study in order to analyze humoral and cell-mediated responses in SARS-CoV-2 positive first complete vaccination patients.

Inclusion Criteria:

• Patients with a complete first-cycle vaccination against SARS-CoV-2 performed 4 to 7 months before.

Exclusion Criteria:

• Presence of malignancy under chemotherapy
• Patient with previous transplantation
• Patient receiving immuno-modulatory or immunosuppressive drugs
• Patient receiving corticosteroid therapy since more than 10 days
• Pregnancy
• Consent withdrawal

Forty-five patients will be totally enrolled in the study. Three cohorts of patients will be considered.

1. Control group: 15 vaccinated patients with a pharyngeal swab negative for SARS-CoV-2 isolation
2. Asymptomatic group: 15 vaccinated patients with a pharyngeal swab positive for SARS-CoV-2 isolation and absence of symptoms related to the infection
3. Symptomatic group: 15 vaccinated patients with a pharyngeal swab positive for SARS-CoV-2 isolation and presence of moderate to severe symptoms related to the infection (i.e. peripheral oxygen saturation lower than 94% in room air)

The individual patients data will be shared only after the publication of the study on an international peer-reviewed journal and on scientific and intelligible proposal

Data will be available after publication on an indexed international and peer-reviewed journal

Access will be allowed after contacting by email the principal investigator, by providing and intelligible and scientific proposal