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.

Background:Current vaccines against SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) and vaccine booster programs aim to reduce hospitalizations due to severe COVID-19 (coronavirus disease 2019). It is now accepted that vaccination does not completely prevent infection and that breakthrough COVID-19 does occur. This study included 53 vaccinated patients who were hospitalized at a single center in Poland with breakthrough COVID-19 and aimed to evaluate the factors associated with their clinical course. Material/Methods: This study covered the period 26 November 2021 to 11 March 2022. All patients had been vaccinated against COVID-19 with one of the following 4 vaccines: the mRNA-1273 (Moderna) mRNA vaccine (Spikevax); the BNT162b2 (Pfizer-BioNTech) mRNA vaccine (nucleoside-modified) (Comirnaty); the Ad26.COV2.S (Janssen/ J0ohnson & Johnson) recombinant vaccine (Jcovden); and the AZD1222 (ChAdOx1) (Oxford/AstraZeneca) recombinant vaccine (Vaxzevria). Results:The course of COVID-19 in vaccinated patients was relatively similar. The patients vaccinated more than 24 weeks earlier rarely needed a stay in the Intensive Care Unit (ICU) (P=0.021), and the occurrence of deaths was significantly lower in this group (P=0.046). Women remained in hospital considerably longer than men (P=0.011). Age and comorbidities did not affect the course of this infection. Conclusions:Despite the many advantages of the COVID-19 vaccination, our observations indicate a potential risk of infection after vaccination. The assessment of the course of COVID-19 in vaccinated patients gives the possibility to compare different vaccines and indicate factors that can reduce immunity.