Great expectations to control the pandemic are placed in vaccines against COVID-19. Currently, the four COVID-19 vaccines approved in the European Union. The investigators designed a study assessing the anti-SARS-CoV-2 IgG antibody titer after vaccination cycle with the BNT162b2 vaccine in several time points relating these results to the COVID-19 history and severity of symptoms during the disease and after the first and second vaccine dose.

The study includes patients of Antoni Jurasz University Hospital No.1 in Bydgoszcz after organ transplantation. To meet the inclusion criteria patients will have to be vaccinated with two doses of the BNT162b2 vaccine. The assessment of the anti-SARS-CoV-2 IgG antibody titer at several time points in each participant. Fresh serum samples were used to measure SARS-CoV-2 IgG on the Siemens Atellica system (Siemens Healthineers, Erlangen, Germany). Results of SARS-CoV-2 IgG were given as U/ml, whereby the cut-off for positivity was defined as ≥1.0 U/ml.

Inclusion Criteria:

• Provision of informed consent to study
• Age ≥ 18 years
• Receiving two doses of the BNT162b2 vaccine
• patients post organ transplantation

Exclusion Criteria:

• patients who did not complete 2-dose vaccination schedule
• patients who received any other vaccine than BNT162b2
• patients considered by investigator to be unable to cooperate

The study patients of Antoni Jurasz University Hospital No.1 in Bydgoszcz who underwent organ transplantation.

Approximately 250 adult participants are planned to be included in the study