Coronaviruses are important causative agents of human and animal diseases. In late 2019, a new coronavirus was identified as the cause of a series of pneumonia cases in Wuhan, a city in China's Hubei province. The virus spread rapidly resulting in an epidemic across China, followed by an increasing number of cases in other countries around the world. The conversion of the Dubrava University Hospital into a Primary Respiratory Intensive Care Center led to organizational, logistical and infrastructural adjustments for the possible admission of a larger number of patients with the disease COVID-19. As time progressed, a vaccine appeared, and thus the need to monitor patients who were sick with COVID-19 and were vaccinated with one or more doses. The aim of this research paper is to compare the characteristics of vaccinated COVID-19 positive patients hospitalized in Dubrava University Hospital in 3 waves of the pandemic. For the purposes of creating the empirical part of this paper, secondary data sources were used and data were collected on patients with COVID-19 who were vaccinated against SARS-CoV-2 in 3 variants of the virus. The paper uses graphic and tabular presentation methods to present the structure of the patient using absolute and relative frequencies. Numerical values are presented using the methods of descriptive statistics, namely the median as the mean value and the interquartile range as an indicator of deviation from the average value. The normality of the distribution of numerical values was previously tested with the Kolmogorov-Smirnov test. Hypotheses were tested using the Chi-square test when examining differences in patient structure among strain variants. The difference in the representation of patients with regard to the number of vaccinations is examined using the Z test of the difference in proportions. After the investigation, it can be concluded that during the COVID-19 pandemic, the number of vaccinated COVID-19 positive hospitalized patients is increasing with the appearance of new variants of the virus. Through this research, we came to the conclusion that male patients are 1.24 times more frequent compared to female patients and that the frequency of male patients compared to female patients is higher when infected with all variants of the virus. The average life expectancy is the highest among patients hospitalized with the Beta variant and is 4 years higher compared to patients hospitalized with the Delta variant, and 3 years higher than patients hospitalized with the Omikron variant, and the presence of a statistically significant difference was determined by the examination. The role of highly educated nurses and technicians during the COVID-19 pandemic is extremely important. Due to the great unknowns at the very beginning of the pandemic, highly educated nurses/technicians demonstrated their competence and willingness to organize a nursing service to work in specific conditions. The key to the protection of nurses/technicians and other health workers is adherence to all procedures for preventing and controlling infection and isolation measures, as well as correct uusage of personal protective equipment. Highly educated medical staff (nurses and technicians) were the main transmitters of knowledge and education of employees and patients about the importance of vaccination. Throughout history, vaccination has proven to be the most effective measure in combating various diseases. As throughout history, vaccination against the disease COVID-19 has proven to be the most effective public health measure to stop the spread of the disease.