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29 April 2023: Database Analysis  

Clinical Course of 53 Previously Vaccinated Patients Admitted to the National Hospital in Warsaw, Poland with COVID-19 Between November 2021 and March 2022

Artur Zaczyński1AB, Michał Hampel1AB, Paweł Piątkiewicz2AB*, Jacek Nasiłowski3AB, Sławomir Butkiewicz2AB, Urszula Religioni4DEF, Agnieszka Barańska5CD, Maria Malm ORCID logo5CD, Agnieszka Neumann-Podczaska ORCID logo6DEF, Regis Vaillancourt2ACDF, Piotr Merks2AFG

DOI: 10.12659/MSM.939841

Med Sci Monit 2023; 29:e939841




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 AND 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.

Keywords: COVID-19 Vaccines, Hospital Mortality, Vaccination, Male, Humans, Female, Poland, Ad26COVS1, BNT162 Vaccine, ChAdOx1 nCoV-19, COVID-19, SARS-CoV-2, Hospitalization, Hospitals, Disease Progression


Since the first case was diagnosed in China, COVID-19 has rapidly spread throughout the world [1]. COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Since the onset of the epidemic, more than 582 million confirmed cases of COVID-19 and 6.41 million deaths have been reported globally (as of 5 August 2022) [2].

As of 5 August 2022, more than 6.08 million people in Poland have been infected with COVID-19, and 117 000 have died [3]. Subsequent SARS-CoV-2 variants that appear in populations raise many clinical concerns [4]. For this reason, the development of a safe and effective vaccine against COVID-19 aroused great global interest and hopes for public health protection [5]. The World Health Organisation (WHO) considers vaccines against COVID-19 as the most effective method to fight this disease [6]. The WHO has approved 9 vaccines against COVID-19: 2 RNA, Moderna (mRNA-1273) and Pfizer/BioNTech (BNT162b2); 3 non-replicating viral vectors, Janssen (Johnson & Johnson) (Ad26.COV2.S), Oxford/AstraZeneca (AZD1222), and Serum Institute of India Covishield (Oxford/AstraZeneca formulation); 2 protein subunits (NVX-CoV2373 and NovaVax); and inactivated virus techniques, Sinopharm (Beijing) BBIBP-CorV (Vero Cells) and Sinovac (CoronaVac) [7]. The vaccines against COVID-19 available in Poland are: the mRNA-1273 (Moderna) mRNA vaccine (Spikevax); the BNT162b2 (Pfizer-BioNTech) mRNA vaccine (nucleoside-modified) (Comirnaty); the Ad26.COV2.S (Janssen/Johnson & Johnson) recombinant vaccine (Jcovden); the AZD1222 (ChAdOx1) (Oxford/AstraZeneca) recombinant vaccine (Vaxzevria), and since 1 March 2022, Nuvaxovid (Novavax) [8]. Apart from the Janssen vaccine, in the basic dosage scheme all the vaccines required 2 doses administered at different time intervals (depending on the vaccine). Since autumn 2021, the third dose of the vaccine against COVID-19 has been authorized in Poland for people vaccinated at least 6 months earlier. Currently, the second booster dose (the fourth in the entire vaccination scheme) is available for people over 60 years of age, and people over 12 years of age with immune disorders who received all basic vaccines and the first booster dose against COVID-19 [9].

Data from randomized clinical studies and observational studies conducted in real time prove that COVID-19 vaccines currently approved for use are safe and effective in preventing serious consequences, hospitalization, and deaths caused by COVID-19 [10]. To achieve herd immunity, at least 60–70% of the population would have to get vaccinated [11,12]. In Poland, 59.4% of the population have been fully vaccinated (2 doses, as of 5 August 2022) [13].

The effectiveness of the vaccines in different groups of patients was assessed by teams all over the world. This data shows a high level of short-term protection of the vaccines against COVID-19 [14]. In the longer term, the results are not evident and indicate, for example, waning vaccine effectiveness several months after vaccination, namely in those aged 65 years or over [10,15], which can be associated with the variability of the virus and the different prevention policies in particular countries [16,17].

Considering the above, the basic objective of this study was to determine the course of COVID-19 in patients vaccinated with one of the vaccines available in Poland, to assess the influence of the type of vaccine on the severity of COVID-19, and to assess the impact of sex, age, and comorbidities. Therefore, 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 and Methods


Data were collected at the National Hospital in Warsaw (Poland) in the period between 26 November 2021 and 11 March 2022 using the Clininet system (https://www.cgm.com/_Resources/Persistent/f7d7adc241aebacc931c3db67f614e963df90dd4/2019-09-09%20CGM%20CLININET%20PL.pdf).

The National Hospital was a temporary hospital arranged at the National Stadium in October 2020 by the Central Clinical Hospital of the Ministry of Interior and Administration to treat patients infected with COVID-19.


Our study included all 53 patients hospitalized due to COVID-19 at that time and fully vaccinated with any vaccine approved in Poland. Each patient had a positive RT-PCR test for SARS-CoV-2 conducted in the hospital. At that time, only the alpha variant of the coronavirus was present and detected in Poland. We defined full vaccination as an administration of at least 2 doses of the Pfizer, Moderna, or AstraZeneca vaccines, or 1 dose of the Jenssen vaccine. The analysis included the test results of all patients present in the hospital at that time, and thus the selection of patients was based on availability.


Statistical analysis was performed with the StatSoft, Inc. (2014) statistic software package, STATISTICA (data analysis software system Cracow, Poland), version 12.0, www.statsoft.com, and Excel Spread Sheet. A P value of <0.05 defined the statistical significance of differences. Continuous variables were reported as means (M)±standard deviation (SD), interquartile range (IQR) and minimum (MIN)-maximum (MAX) range. To determine the relationship between the variables, the following tests and statistical coefficients were used: Kruskal-Wallis rank sum test, analysis of variance (ANOVA), and Fisher’s exact test. Before tests were applied, assumptions on the normality of distribution were verified by means of the Shapiro-Wilk test.



The analysis comprised 53 patients. The mean age of the patients was 63.8±9.8 years; the youngest was 44, and the oldest was 83 years old. The percentage of men was slightly higher than women (56.6% vs 43.4%, respectively). BMI of the patients ranged from 20.7 to 43, and half of the patients had BMI of 28.10 or higher. Demographic characteristics of the patients are presented in Table 1.

All the patients were vaccinated against COVID-19 caused by SARS-CoV-2, of which 43.4% were vaccinated with the Pfizer vaccine, 32.1% with AstraZeneca, 17.0% with Moderna, and 7.5% with Johnson. The vast majority of the patients received 2 doses (73.6%), 1 dose (24.5%), and 1 patient had 3 doses; 92.5% of the patients were fully vaccinated (received at least 1 dose of the Johnson vaccine or at least 2 doses of the AstraZeneca, Moderna, or Pfizer vaccine). The period between the last dose of the vaccine and diagnosis of infection was 0.6–38 weeks, and was at least 23.71 weeks in half of the patients (Table 2).

There were practically no addictions among the patients. Their comorbidities included hypertension (62.3%), diabetes (28.2%), hypothyroidism (18.9%), atherosclerosis (17%), autoimmune diseases (17%), cancer (13.2%), and asthma/COPD (5.7%).

Hospitalization of the patients infected with COVID-19 lasted from 1 to 33 days, and half of the patients were hospitalized for 11.5 days or longer. Nearly one-fifth of the patients (18.9%) had to stay in the ICU for 8.5±4.0 days on average, and 17% of the hospitalized patients died.

Regarding data on the vital signs and condition of the patients infected with COVID-19 on admission, the average heart rate was 87.7±14.7 beats per minute, the average systolic blood pressure was 135.4±21.3 mmHg, and the average diastolic blood pressure was 80.7±13.3 mmHg. The third quartile for temperature was 37.70°C, which indicates that the vast majority of the patients did not have a high temperature on admission. During O2 supplementation, half of the patients had an oxygen saturation of 94% or lower, and an oxygen partial pressure of 44.95 mmHg or lower.

On admission, one-third of the COVID-19 patients received oxygen therapy in the form of a nasal canula (34%), and more than one-fourth used a non-rebreather mask (28.3%). Simple oxygen masks and NIV (non-invasive ventilation) were used less frequently (9.4% and 1.9%, respectively), and one-fourth of the patients were not given oxygen therapy upon admission. Computed tomography revealed lung involvement ranging from 0% to 80%, with at least 30% in half of the patients.

During hospitalization, 62.3% of the patients experienced worsening of their condition and required a more invasive form of oxygen therapy, and 7.5% of the patients improved; 30.2% of the patients did not require a change in oxygen therapy. During hospitalization, 13.2% of the COVID-19 patients did not require oxygen therapy, which was significantly less compared to 26.4% on admission. Nasal cannulas (20.8% vs 34%) and non-rebreather masks (24.5% vs 28.3%) were less frequently used, and simple oxygen masks (13.2% vs 9.4%), high-flow oxygen therapy (7.5% compared to 0%), NIV (9.4% vs 1.9%), and respiratory therapy (11.3% vs 0%) were more frequent.

Regarding medications administered during hospitalization, the vast majority of the COVID-19 patients were given Dexaven/Demezon (81.1%) and heparin (94.3%), while Olumiant (11.3%) and Remdesivir (11.3%) were less common.


No significant influence of the type of vaccine on the severity of the infection was shown (Table 3). Patients who had been administered the Pfizer vaccine stayed slightly longer in the ICU, and the lowest percentage of lung involvement was recorded in the patients vaccinated with the Moderna vaccine. It was also noted that the patients who had been given the Moderna vaccine were more likely to experience respiratory deterioration and require changing the intensity of oxygen therapy. These outcomes were not statistically significant. The logistic regression analysis revealed that the patients vaccinated with the Pfizer vaccine were significantly less likely to experience respiratory deterioration than those who had received the AstraZeneca vaccine (OR=0.196; 95% CI: 0.0375–0.799; P=0.032).


Patients vaccinated more than 24 weeks earlier were by far the least likely to require a stay in the ICU (P=0.021), and deaths were also significantly less frequent in this group (P=0.046). Respiratory deterioration and the resulting need to increase the intensity of oxygen therapy were most often observed in patients who had been vaccinated between 2 and 20 weeks earlier, but the result of the Fisher’s exact test was not statistically significant (P=0.110). The impact of time on the severity of the infection is presented in Table 4.


No significant influence of age on the severity of COVID-19 was found (Table 5). The length of a stay in the ICU was slightly shorter in patients aged 65–69, and the change of oxygen therapy due to respiratory deterioration was the least frequent in the patients aged more than 69, who were more likely to have no changes in oxygen therapy compared to others. The differences were not statistically significant.

Statistical analysis showed that women remained in hospital considerably longer than the men (P=0.011). The time spent in hospital in half of the women was 15 days, while in the men the median length of hospitalization was 10 days. The women on average spent more time in the ICU, but the difference was not statistically significant (P=0.315). No significant impact of sex on the remaining aspects of COVID-19 was noted.

Practically no significant influence of comorbidities on the severity of COVID-19 was recorded. Patients with hypertension were significantly more likely to need a non-rebreather mask during oxygen therapy (42.4% vs 5%), yet the simple oxygen mask (3% compared to 20%) and nasal canula (27.3% vs 45%) were considerably less frequently used (P=0.008). In patients with hypothyroidism, CT revealed a significantly lower percentage of lung involvement (P=0.008). In half of the patients with hypothyroidism, lung involvement was up to 10%, and in half of the patients without hypothyroidism it was up to 30%.


This study, including 53 patients hospitalized in the National Hospital in Warsaw, Poland, shows that the various vaccines against COVID-19 have a similar influence on the course of this disease. Slight differences were observed in the length of a stay in the ICU (slightly longer in the case of the Pfizer vaccine), the degree of lung involvement (lowest in patients vaccinated with the Moderna vaccine), and respiratory function (lowest risk of respiratory deterioration in the patients who received the Pfizer vaccine).

The time from vaccination had a significant impact on ICU stay and risk of death, which were least frequent in patients vaccinated at least 24 weeks before becoming infected. It was also observed that women had a longer hospitalization. This effect was very slight in the case of age, and was not noted in terms of comorbidities.

Current studies directly indicate that the advantages of COVID-19 vaccines outweigh the risk, despite rare serious adverse effects [18,19]. Not only do vaccinations influence the frequency of infection, but also deaths and severity of infection [7,16]. Fiolet et al [18] found a similar efficacy of vaccines; the efficacy of the mRNA vaccine against hospitalization and death was 87–94%. Ghazy et al report that inactivated COVID-19 vaccine (CoronaVac) is safe in the case of hospitalization (87.5%) and death (86.3%). Similar results were observed in elderly people, which confirms similar efficacy of vaccines [7].

Studies conducted to date have not produced unequivocal evidence [5,14,19–22], and their authors indicate many determinants that influence the final outcomes of vaccinations. Although all the vaccines against COVID-19 were highly effective against the original strain, these effects are currently different due to the consequences of the variants of the virus [18].

Studies indicate reduced effectiveness of the vaccines in relation to hospitalization due to COVID-19 variants, and link this effect to an increase in the prevalence of Delta variant infections. Rosenberg et al found that the COVID-19 vaccines were highly effective against hospitalization (VE > 90%) in fully vaccinated patients, even in the period with an increased occurrence of the Delta variant [10], while non-vaccinated persons were more often hospitalized at that time. These differences have also been noted in other studies [23].

Studies also revealed reduced immunity over time since vaccination. For example, a study carried out in the United States indicated that 3 months after vaccination, the greatest decreases in the effectiveness of the vaccines were observed among patients vaccinated with the Pfizer BNT162b2 vaccine. The effectiveness of vaccines against hospitalization due to COVID-19 remains high. The lowest effectiveness against hospitalization was observed among people over age 65 and those vaccinated with the Janssen Ad26.COV2.S vaccine. Higher effectiveness against COVID-19 was observed in recently vaccinated people, particularly in the case of the Moderna mRNA-1273 vaccine [17].

Other studies confirm that a severe course of COVID-19 after vaccination occurs mainly in elderly populations, especially among people living in long-term care facilities [24,25]. Andrews et al also reported that reduced effectiveness of vaccines seems to be more likely among extremely clinically vulnerable elderly people [26]. In turn, the study by Wang et al showed an increased risk of infection in vaccinated cancer patients, especially those undergoing active cancer care, which was associated with a significant risk of hospitalization and mortality [27]. The formulation may also be important, with some studies indicating that a more severe course was reported in those who had received the Pfizer BNT162b2 vaccine [24,25]. Another study shows reduced effectiveness of the Moderna vaccine against the Delta [28] variant, similar to other studies [29].

An English study confirmed that protection against hospitalization and death due to COVID-19 remains at a high level for at least 20 weeks after receiving the second dose (the analysis comprised Pfizer and AstraZeneca vaccines) [21], but a decreased protection against infection was observed after 6 months. The effect of time is unclear. Some studies reported minimally decreased effectiveness of the vaccines over time, while others showed significant changes (protection reduction by >25%) [18,30]. A study by Andrews et al provided evidence of waning post-vaccination protection against symptomatic infection, but with protection against hospitalization and death remaining at a high level for at least 20 weeks after the second dose [14].

Summing up, the COVID-19 pandemic has changed since the development of the vaccines, which has been reflected in the severe courses and deaths, especially in patients over the age of 60 [31].

The analysis of studies indicates that reduced effectiveness of the vaccines over time has 3 potential explanations: it reflects lower effectiveness of a vaccine against a new variant, is a sign of real immunodeficiency due to a loss of immune protection, and bias of the studies [18,29].

The US Centers for Disease Control and Prevention indicate that real-world effectiveness of vaccines can be influenced by several factors, including host population factors (eg, those who were not included in clinical studies), viral factors (eg, variants), and program/political factors (eg, adhering to dosage schemes or storage/handling of the vaccines) [32].

The effectiveness of booster doses of the vaccines against COVID-19 has been emphasized. For example, a study by Bard et al showed that a booster dose increased the effectiveness of vaccines compared to people who received only the first series [33].

Like all studies, this also has some limitations. First, it comprised a relatively small group of patients hospitalized in a single facility. In addition, we assessed patients in a very short time interval. At the planning stage of the study, we did not take into account the interval between the vaccine and the disease, which may also have affected the results. Currently, the administration of the fourth dose of the vaccines to patients may also impact the outcomes.


The vaccines are an effective tool for preventing a severe course, hospitalization, and death due to COVID-19. Despite using the vaccines, COVID-19 remains a considerable challenge for public health worldwide, with a potential risk of infection after vaccination. Our study, conducted on a group of several dozen patients hospitalized in a National Hospital in Poland showed a relationship between the interval since the last vaccination and the course of the disease. However, there were no significant relationships between the course of infection severity and comorbidities. Although our study shows a relatively similar course of COVID-19 in vaccinated persons, the variability of the virus variants and waning immunity can influence the severity of the course of this disease and the risk of death. Thus, monitoring the effectiveness of the vaccinations is essential in understanding the scale and source of the variability of their effectiveness. Identification of groups at risk of waning immunity is of great importance. These activities will impact the effectiveness of the vaccination coverage level, the change of public health policy, and recommendations regarding vaccinations.


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Medical Science Monitor eISSN: 1643-3750
Medical Science Monitor eISSN: 1643-3750