Introduction. Studies to date indicate the relatively high effectiveness of vaccinations in preventing severe COVID-19 symptoms. However, in Poland, 40% of the population remains unvaccinated. Objective. The objective of this study was to describe the natural history of COVID-19 in unvaccinated hospital patients in Warsaw, Poland. Material and methods. This study evaluated data from 50 adult patients from the National Hospital in Warsaw, Poland, in the period 26 November 2021 to 11 March 2022. None of these patients had been vaccinated against COVID-19. Results. Analysis showed that the average hospitalisation time for these unvaccinated COVID-19 patients was 13 days. Clinical deterioration was observed in 70% of these patients, 40% required the intensive care unit, and 34% subsequently died prior to the end of the study. Conclusions. There was a significant deterioration and high mortality rate in the unvaccinated patients. For this reason, it seems prudent to take measures to increase the vaccination coverage level of the population against COVID-19.