Background: In the last days of December 2020, the SARS-CoV-2 virus vaccine BNT162b2 (Comirnaty, Pfizer-BioNTech) was introduced, for the first time, for wide use in Poland. According to the vaccination schedule, healthcare workers were the first to receive the vaccine. The aim of this study was to analyse the attitudes of those who were determined to be vaccinated, with particular reference to their concerns, attitudes towards vaccination advocacy and sources of knowledge on vaccination, as well as the incidence of adverse reactions. Methods: The study had a three-stage design. Respondents completed a self-administered questionnaire before receiving the 1st and 2nd vaccine doses and 2 weeks after receiving the 2nd dose. A total of 2247 responses were obtained (1340 responses in the first stage, 769 in the second and 138 in the third). Results: The main source of knowledge on vaccination was the Internet (32%;n= 428). Of the respondents, 6% (n= 86) reported anxiety before the 1st dose of the vaccine, which increased to 20% (n= 157) before the 2nd dose. A declaration of willingness to promote vaccination among their families was made by 87% (n= 1165). Among adverse reactions after the 1st dose of the vaccine, respondents most frequently observed pain at the injection site (n= 584; 71%), fatigue (n= 126; 16%) and malaise (n= 86; 11%). The mean duration of symptoms was 2.38 days (SD 1.88). After the 2nd dose of vaccine, similar adverse reactions—pain at the injection site (n= 103; 75%), fatigue (n= 28; 20%), malaise (n= 22; 16%)—predominated among respondents. Those who declared having had a SARS-CoV-2 virus infection (p= 0.00484) and with a history of adverse vaccination reactions (p= 0.00374) were statistically more likely to observe adverse symptoms after vaccination. Conclusions: Adverse postvaccinal reactions are relatively common after Comirnaty vaccination but are usually mild and transient in nature. It is in the interest of public health to increase the knowledge of vaccine safety.