Background: The development of vaccines against COVID-19 has greatly altered the natural course of this infection, reducing the disease’s severity and patients’ hospitalization. However, hesitancy against vaccination remains an obstacle in the attempt to achieve appropriate herd immunity that could reduce the spread of SARS-CoV-2. The aim of this study was to investigate the perceptions and attitudes of COVID-19 patients hospitalized during the fourth pandemic wave in two Greek hospitals and assess whether their experience had changed their intentions regarding vaccination against COVID-19. Methods: This is a cross-sectional, questionnaire-based survey, conducted from 31 August 2021 to 18 February 2022 in the COVID-19 departments of two tertiary care hospitals. The questionnaire included questions regarding the patients’ educational level, knowledge and beliefs regarding SARS-CoV-2, personal protection measures, beliefs regarding vaccination, vaccination status, reasons for not been vaccinated against SARS-CoV-2, feelings of regret for not been vaccinated, and willingness to be vaccinated in the future. All adult patients with COVID-19 were eligible, regardless of their vaccination status against SARS-CoV-2. Results: In total, 162 patients agreed and participated in the study, with 97% of them suffering severe COVID-19. Their median age was 56 years, and 59.9% (97 patients) were male. Among them, 43.8% had been vaccinated against COVID-19. When unvaccinated patients were asked the reasons for not being vaccinated, the most frequent responses were that they were waiting for more scientific data, due to uncertainty about long-term consequences of the vaccine, and their fear of thrombosis. When at discharge, unvaccinated hospitalized COVID-19 patients were asked whether they would get vaccinated if they could turn time back, and 64.7% of them replied positively. Conclusions: The study reveals several patients’ fears and misconceptions and suggests that there is room for implementing measures that could reduce knowledge gaps allowing for improvement of vaccination rates against COVID-19.