Abstract
Background
Vaccination against SARS-CoV-2 has been crucial in impeding virus spread and preventing fatal complications. Despite growing evidence of vaccine efficacy, data on its impact on hospitalized patients remain limited. We aimed to estimate the risk of mortality, ICU admission, and hospitalization length among hospitalized COVID-19 patients based on vaccination status.
Methods
In this single-center cross-sectional study, we included patients above 16 years old hospitalized due to COVID-19. Patients were categorized as unvaccinated, partially vaccinated (single dose), or fully vaccinated (at least one booster dose). We performed logistic and linear regression analyses, including both bivariable and multivariable models, to evaluate the association between vaccination status, demographic characteristics, and study outcomes.
Results
Of 299 participants, 21.7%, 15.7%, and 62.5% were unvaccinated, partially vaccinated, and fully vaccinated, respectively. Full vaccination was associated with significantly reduced mortality risk (OR: 0.235, 95%CI: 0.103–0.538) and lower ICU admission rates (OR: 0.252, 95%CI: 0.131–0.484). Vaccinated patients had shorter hospital stays (fully vaccinated: 6.38 ± 1.65 days; unvaccinated: 9.22 ± 2.84 days, p < 0.001). Older age independently predicted higher mortality (OR: 1.062, 95%CI: 1.030–1.095), ICU admission (OR: 1.047, 95%CI: 1.027–1.068), and longer hospital stays (estimate: 0.027, 95%CI: 0.012–0.043). Multiple comorbidities were associated with higher mortality and longer hospitalization (OR: 1.794, 95%CI: 1.244–2.587; estimate: 0.395, 95%CI: 0.142–0.648).
Conclusion
Full vaccination against SARS-CoV-2 is associated with significantly improved clinical outcomes in hospitalized COVID-19 patients, including reduced mortality, lower ICU admission rates, and shorter hospital stays.
Supplementary Information
The online version contains supplementary material available at 10.1186/s12879-025-10530-4.
Keywords: COVID-19, SARS-CoV-2, Vaccine, Hospital Mortality, Hospitalization, Intensive Care Unit
Introduction
Severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2) is responsible for the highly contagious and potentially life-threatening COVID-19 [1]. Since the first reports of COVID-19 in December 2019 in Wuhan, China, over 767 million cases have been identified, resulting in approximately 6.95 million deaths by July 2023 [2]. Respiratory particles are the major source of transmission, mostly during face-to-face contact and in places with poor ventilation [2, 3]. Presymptomatic transmission is believed to be the main contributor to the spread of SARS-CoV-2, as viral transmission begins 2–3 days before symptom manifestation, and the viral load in the upper respiratory tract peaks around symptom onset [4].
Although most of the patients experience mild courses of the disease, and some may even remain asymptomatic, nearly 15% of cases deteriorate to severe COVID-19, leading to acute respiratory distress syndrome (ARDS), multi-organ failure, and death [5, 6]. Among many risk factors for progressing to severe COVID-19, advanced age, male gender, and existing comorbidities, like diabetes and hypertension, are best known [7].
As preventive measures like wearing facial masks and maintaining social distancing have not been sufficient to fully control the spread of the virus, vaccine development, and public vaccination remained a priority [8, 9]. Many studies have reported significant reductions in COVID-19 infection, severity, ICU admission, and mortality following vaccination [10–13]. A systematic review and meta-analysis comprising 52 studies on different populations with COVID-19 revealed that vaccination against SARS-CoV-2 is associated with a lower incidence rate, hospitalization, and COVID-related mortality [9].
In this study, we aim to assess the effect of vaccination on the outcome of hospitalized COVID-19 patients, including mortality, ICU admission risk, and the length of hospitalization.
Methods
Design and participants
This is a cross-sectional study conducted at Firoozgar Hospital in Tehran, Iran. All patients above 16 years old hospitalized due to COVID-19 between April 2021 and March 2022 were considered eligible for the study. The diagnosis of COVID-19 was based on positive results from real-time Reverse Transcription Polymerase Chain Reaction (RT-PCR) for SARS-CoV-2. After receiving approval from the Ethics Committee of the Iran University of Medical Sciences (IUMS), the research team gathered data from hospital patients’ files.
The primary endpoints of our study were to estimate and compare the risk of mortality and ICU admission among hospitalized COVID-19 patients based on vaccination status. Our key secondary endpoint was to evaluate the association between vaccination status and hospitalization length. The association between vaccination status and the severity of COVID-19-related pulmonary damage, as well as general characteristics, were other secondary endpoints.
Measurements
Patients who had not received any dose of available COVID-19 vaccines were considered unvaccinated. Patients who had received only one shot of the vaccine were considered partially vaccinated. If patients received at least one booster dose, they were categorized as fully vaccinated.
Based on the findings of chest computed tomography (CT) scans, the severity of lung involvement is scored for each pulmonary lobe as follows: 0: clear lung, 1: less than 5%, 2: 5–25%, 3: 25–50%, 4: 50–75%, 5: more than 75%. After summing the scores of the five pulmonary lobes, the total score ranges from 0 (without any COVID-19-related pulmonary damage visible in the CT scan) to 25 (severe lung damage) and is categorized as mild (≤ 8), moderate (9–15), or severe (≥ 16).
Statistical analysis
The frequency and percentage for categorical variables and mean ± standard deviation (SD) for continuous variables is demonstrated. The normality of data is assessed by the Kolmogorov–Smirnov test and Q-Q plots. Chi-squared test and independent samples t-test are used to compare categorical and continuous variables, respectively. To compare continuous variables among three levels of vaccination status, we used one-way analysis of variance (ANOVA). Binary logistic regression is performed to calculate the risks of mortality and ICU admission based on bivariable and multivariable analyses. Linear regression analyses were performed for estimates of hospitalization length and chest CT score in association with study variables. A p-value less than 0.05 is considered significant for all analyses. Data analysis was done using SPSS software version 18.
Results
General characteristics
We recruited 299 eligible participants in this study. The participants’ ages ranged from 16 to > 90 years, with a mean of 62.7 ± 17.6 y/o. One-hundred forty-six (48.8%) were male, and 153 (51.2%) were female. The majority of participants (97.3%) lived in urban areas. Overall, 189 (63.2%) patients had at least one comorbidity, including hypertension in 142 (47.5%), diabetes in 98 (32.8%), coronary artery disease (CAD) in 68 (22.7%), and chronic kidney disease (CKD) in 36 (12%) patients. Of the patients, 78 (26.1%) had only one comorbidity, 69 (23.1%) had two comorbidities, 40 (13.4%) had three comorbidities, and 2 (0.7%) presented with all four underlying diseases. (Table 1).
Table 1.
General characteristics of hospitalized COVID-19 patients in total and in vaccination groups
| Total N = 299 |
Unvaccinated N = 65 (21.7%) |
Partially vaccinated N = 47 (15.7%) |
Fully vaccinated N = 187 (62.5%) |
p-value | |
|---|---|---|---|---|---|
| Gender (Male) | 146 (48.8%) | 31 (47.7%) | 26 (55.3%) | 89 (47.6%) | 0.625 |
| Age (Mean ± SD) | 62.7 ± 17.6 | 66.4 ± 16.7 | 61.7 ± 17.6 | 61.7 ± 17.8 | 0.161 |
| Having a comorbidity | 189 (63.2%) | 39 (60%) | 28 (59.6%) | 122 (65.2%) | 0.642 |
| Diabetes (Yes) | 98 (32.8%) | 19 (29.2%) | 17 (36.2%) | 62 (33.2%) | 0.730 |
| Hypertension (Yes) | 142 (47.5%) | 29 (44.6%) | 17 (36.2%) | 96 (51.3%) | 0.154 |
| Coronary Artery Disease (CAD) (Yes) | 68 (22.7%) | 13 (20%) | 11 (23.4%) | 44 (23.5%) | 0.837 |
| Chronic Kidney Disease (CKD) (Yes) | 36 (12%) | 6 (9.2%) | 5 (10.6%) | 25 (13.4%) | 0.643 |
| Number of comorbidities (Mean ± SD) | 1.1 ± 1.0 | 1.0 ± 1.0 | 1.0 ± 1.0 | 1.2 ± 1.1 | 0.422 |
| Outcome (Death) | 54 (18.1%) | 19 (29.2%) | 16 (34%) | 19 (10.2%) | < 0.001 |
| ICU admitted (Yes) | 116 (38.8%) | 40 (61.5%) | 20 (42.6%) | 56 (29.9%) | < 0.001 |
| Hospitalization length (Days) (Mean ± SD) | 7.1 ± 2.4 | 9.22 ± 2.84 | 7.19 ± 2.61 | 6.38 ± 1.65 | < 0.001 |
| Lung CT scan severity | |||||
| Mild | 103 (34.4%) | 9 (13.8%) | 12 (25.5%) | 82 (43.9%) | < 0.001 |
| Moderate | 111 (37.1%) | 28 (43.1%) | 17 (36.2%) | 66 (35.3%) | |
| Severe | 85 (28.4%) | 28 (43.1%) | 18 (38.3%) | 39 (20.9%) | |
Vaccination status
Out of the 299 participants, 65 (21.7%) were unvaccinated, 47 (15.7%) were partially vaccinated, and 187 (62.5%) were fully vaccinated. Our patients received vaccinations from six different brands: Sinopharm (BBIBP- CorV) (82.1%), Oxford–AstraZeneca (ChAdOx1) (10.7%), Sputnik V (3.8%), COVIran Barekat, COVAX-19/SpikoGen, and Covaxin (BBV152) (0.4% each). Additionally, five patients (2.1%) received both Oxford–AstraZeneca and Sinopharm doses as their first and booster shots. Among the vaccinated patients, 47 (20.1%) received only one dose, 135 (57.7%) received one booster dose, and 52 (22.2%) received a second booster dose. One-hundred fifteen (49.1%) patients had received the last vaccine dose within one month prior to hospitalization, 155 (66.2%) within two months, 214 (91.5%) within three months, 227 (97%) within four months, and 232 (99.1%) within five months. Two patients (0.8%) reported vaccination with the last dose in six and eight months before admission.
COVID-19-related mortality
Fifty-four (18.1%) of our patients sadly died. The outcome of mortality was observed in 19 (29.2%) unvaccinated, 16 (34%) partially vaccinated, and 19 (10.2%) fully vaccinated patients. (Additional file 1).
According to logistic regression analyses, older age (Odds ratio (OR): 1.074, 95% confidence interval (CI): 1.047–1.102), a higher number of presenting comorbidities (OR: 2.078, 95%CI: 1.557–2.774), and longer intervals from vaccination to hospitalization (OR: 1.366, 95%CI: 1.058–1.763), were associated with higher mortality (Fig. 1).
Fig. 1.
Forest plots of the univariate logistic regression analyses for the outcome of mortality. Bivariable and multivariable models are depicted as (a) and (b), respectively
Being fully vaccinated, regardless of the vaccine type, was a significant predictor of reduced risk of mortality (OR: 0.274, 95%CI: 0.134–0.560). There was no significant association between gender type and mortality (OR: 0.606, 95%CI: 0.275–1.337). Additionally, none of the four underlying diseases alone could predict mortality when controlled for age.
In a multivariable analysis, older age (OR: 1.062, 95%CI: 1.030–1.095), higher number of comorbidities (OR: 1.794, 95%CI: 1.244–2.587), and being fully vaccinated (OR: 0.235, 95%CI: 0.103–0.538) were significant predictors of mortality in our patients. (Table 2).
Table 2.
Univariate logistic regression analyses for the outcome of mortality
| Bivariable analysis | Multivariable analysis | |||||||
|---|---|---|---|---|---|---|---|---|
| p-value | OR | 95% CI | p-value | OR | 95% CI | |||
| Lower | Upper | Lower | Upper | |||||
| Gender (Male) a | 0.849 | 1.059 | 0.587 | 1.909 | 0.716 | 1.138 | 0.567 | 2.281 |
| Age | < 0.001 | 1.074 | 1.047 | 1.102 | < 0.001 | 1.062 | 1.030 | 1.095 |
| Number of comorbidities | < 0.001 | 2.078 | 1.557 | 2.774 | 0.002 | 1.794 | 1.244 | 2.587 |
| Vaccination status b | ||||||||
| Partially vaccinated | 0.588 | 1.25 | 0.558 | 2.798 | 0.290 | 1.684 | 0.641 | 4.421 |
| Fully vaccinated | < 0.001 | 0.274 | 0.134 | 0.560 | < 0.001 | 0.235 | 0.103 | 0.538 |
| Interval from vaccination to hospitalization | 0.017 | 1.366 | 1.058 | 1.763 | - | |||
OR Odds Ratio, CI Confidence Interval
aReference: Female
bReference: Unvaccinated
ICU admission
A total of 116 patients were admitted to the ICU. ICU admission rates were 40 (61.5%) for unvaccinated, 20 (42.6%) for partially vaccinated, and 56 (29.9%) for fully vaccinated patients. (Additional file 2).
In bivariable regression analyses, older age (OR: 1.053, 95%CI:1.035–1.070), higher number of comorbidities (OR: 1.542, 95%CI:1.235–1.925), being partially (OR: 0.463, 95%CI:0.216–0.994) or fully (OR: 0.267, 95%CI: 0.148–0.482) vaccinated were found to be significant predictors of ICU admission risk (Fig. 2).
Fig. 2.
Forest plots of the univariate logistic regression analyses for the risk of ICU admission. Bivariable and multivariable models are depicted as (a) and (b), respectively
However, in a multivariable regression analysis, only older age (OR: 1.047, 95%CI: 1.027–1.068) and receiving full vaccination (OR: 0.252, 95%CI: 0.131–0.484) were associated with ICU admission risk. (Table 3).
Table 3.
Univariate logistic regression analyses for the risk of ICU admission
| Bivariable analysis | Multivariable analysis | |||||||
|---|---|---|---|---|---|---|---|---|
| p-value | OR | 95% CI | p-value | OR | 95% CI | |||
| Lower | Upper | Lower | Upper | |||||
| Gender (Male) a | 0.271 | 0.769 | 0.482 | 1.227 | 0.459 | 0.820 | 0.484 | 1.388 |
| Age | < 0.001 | 1.053 | 1.035 | 1.070 | < 0.001 | 1.047 | 1.027 | 1.068 |
| Number of comorbidities | < 0.001 | 1.542 | 1.235 | 1.925 | 0.226 | 1.186 | 0.900 | 1.565 |
| Vaccination status b | ||||||||
| Partially vaccinated | 0.048 | 0.463 | 0.216 | 0.994 | 0.111 | 0.507 | 0.220 | 1.170 |
| Fully vaccinated | < 0.001 | 0.267 | 0.148 | 0.482 | < 0.001 | 0.252 | 0.131 | 0.484 |
| Interval from vaccination to hospitalization | 0.122 | 1.174 | 0.958 | 1.437 | - | |||
OR Odds ratio, CI Confidence interval
aReference: female
bReference: unvaccinated
Furthermore, none of the four underlying diseases could predict the risk of ICU admission when the analysis was controlled for age.
Hospitalization length and chest CT score
In this study, the minimum and maximum length of hospital stays were 3 and 17 days respectively, with an average of 7.12 ± 2.41 days. Unvaccinated, partially vaccinated, and fully vaccinated patients had on average 9.22 ± 2.84, 7.19 ± 2.61, and 6.38 ± 1.65 days of hospital stay, respectively. (Table 1).
According to linear regression analysis, older age (estimate: 0.027, p < 0.001), a higher number of presenting comorbidities (estimate: 0.251, p = 0.047), and receiving vaccination (estimate: −1.339, p < 0.001) were significantly associated with the length of hospitalization. The results also demonstrated that the interval from vaccination to hospitalization and gender could not predict the length of hospitalization in our patients. (Table 4).
Table 4.
Linear regression analyses on the length of hospitalization
| Bivariable analyses | Multivariable analysis | |||||||
|---|---|---|---|---|---|---|---|---|
| Unstandardized Coefficients (B) | p-value | 95% Confidence interval | Unstandardized Coefficients (B) | p-value | 95% Confidence interval | |||
| Lower | Upper | Lower | Upper | |||||
|
Gender (female:0, male:1) |
−0.054 | 0.846 | −0.605 | 0.496 | 0.110 | 0.637 | −0.349 | 0.57 |
| Age | 0.046 | < 0.001 | 0.031 | 0.061 | 0.027 | < 0.001 | 0.012 | 0.043 |
| Number of comorbidities | 0.549 | < 0.001 | 0.303 | 0.796 | 0.395 | 0.002 | 0.142 | 0.648 |
|
Vaccination status (unvaccinated:0, fully vaccinated:2) |
−1.360 | < 0.001 | −1.657 | −1.064 | −1.339 | < 0.001 | −1.621 | −1.058 |
| Interval from vaccination to hospitalization | 0.128 | 0.172 | −0.056 | 0.311 | - | |||
Based on the lung damage severity presenting in chest CT scan, the frequency of patients within mild, moderate, and severe groups was 103 (34.4%), 111 (37.1%), and 85 (28.4%), respectively (Table 1). When controlled for age, vaccination was significantly associated with less severity of lung damage (unstandardized coefficient (B): −0.244, 95%CI: −0.345-(−0.142)).
Discussion
In this single-center, cross-sectional study on hospitalized patients with COVID-19, we observed significantly lower mortality, hospitalization length, and ICU admission risk associated with COVID-19 vaccination.
A multi-center retrospective study involving 29,732 hospitalized COVID-19 patients reported older age (OR: 1.04, CI: 1.036–1.045) and vaccination (OR: 0.666, 95% CI: 0.580–0.764) as significant predictors of in-hospital mortality. Vaccination was also associated with decreased hospitalization length (−2.13 days, CI: 2.73–1.55 days) [14]. Samara et al. conducted a single-center study in central Greece on 760 hospitalized COVID-19 patients, in which male gender (OR: 2.29, p = 0.013), increased age (OR: 1.12, p < 0.001), and vaccination (OR: 0.2, p < 0.001) were significantly associated with COVID-19-related mortality. However, The length of hospitalization was not statistically significantly lower in vaccinated patients than in the unvaccinated group (p = 0.138) [15].
Our study results revealed that advanced age and vaccination status are significant risk factors for mortality attributed to COVID-19. Moreover, the length of hospitalization was significantly lower in patients with a vaccination history (Table 1). We also observed a direct association between the interval from vaccination to hospitalization and mortality, which is consistent with previous studies [16].
A multicenter study with 2,110 hospitalized COVID-19 patients declared that being unvaccinated is the most prominent independent risk factor for ICU admission (OR: 2.06, 95% CI: 1.64–2.59). They also reported advanced age (OR: 1.02, 95% CI: 1.01–1.02) and having at least one comorbidity (OR: 1.56, 95% CI: 1.15–2.11) as other risk factors for ICU admission [12]. Notably, Valeanu et al. showed that even in patients with severe COVID-19 admitted to the ICU, being fully vaccinated (defined as receiving two vaccine doses) is associated with lower mortality [17]. However, in a study conducted by Van Diepen and colleagues on COVID-19 patients admitted to ICU, in-hospital mortality was found to be similar between unvaccinated and fully vaccinated patients, using propensity-matched analysis (31.8% vs. 34.0%, respectively, adjusted OR: 1.25, 95% CI: 0.97–1.61) [18]. Their results may indicate the potential effectiveness of COVID-19 vaccines in preventing severe disease rather than reducing the mortality risk of critically ill patients. It is also crucial to note that different ICU capacities, healthcare infrastructure, and patient management protocols potentially contribute to different results in research involving COVID-19 outcomes in ICU-admitted patients. Our multivariable regression analysis showed that advanced age (OR: 1.037, 95% CI: 1.016–1.058) and vaccination (OR: 0.312, 95% CI: 0.169–0.578) are independent risk factors for ICU admission.
A meta-analysis of fifty-five studies involving 10,014 patients revealed that the presence of at least one comorbidity in COVID-19 patients leads to a significantly higher risk of severe disease (OR: 3.13, 95%CI: 2.26–4.32) [19]. Pre-existing metabolic comorbidities, like diabetes and hypertension, CVD, and CKD predispose patients to severe COVID-19 through several mechanisms that involve systemic inflammation, immune system impairment, oxidative stress, and endothelial dysfunction [20]. In our study, a higher number of comorbidities were consistently associated with worse outcomes, underscoring the importance of vaccination for vulnerable populations.
In a retrospective cohort study by Costa et al. involving 1,921 hospitalized COVID-19 patients, significantly higher mortality (60.8% vs. 37.4%, p < 0.001) and ICU admission rates (60.9% vs. 46.1%, p < 0.001) were observed in unvaccinated compared to vaccinated patients. Additionally, among vaccinated patients, in-hospital mortality and ICU admission rates were 39.9% and 44.9%, respectively, after the first dose, and 4.4% and 16.7%, respectively, after the third dose [11]. A prospective cohort study in Thailand involving 2,407,315 patients who received at least one dose of COVID-19 vaccine showed that receiving every additional dose of vaccine is associated with an 18%, 25%, and 96% risk reduction in breakthrough infection, hospitalization, and mortality, respectively [21]. In our study, while full vaccination was a significant and independent predictor of lower mortality and ICU admission risk, this association was not significant for partially vaccinated patients.
Several vaccines have been developed for COVID-19 with various types, using the inactivated virus in Bharat, Sinopharm [22], and COVIran Barekat [23], a virus protein subunit in COVAX-19/SpikoGen [24], and an adenovirus vector in AstraZeneca and Sputnik V [25]. Although various efficacies have been established for different COVID-19 vaccines [6, 22], A meta-analysis in 2021 involving seven studies and 1,366,700 patients, revealed that vaccination is effective in preventing severe COVID-19, regardless of the type of vaccine [8]. Overall, receiving vaccination against COVID-19 should be encouraged to impede the rapid progression of the virus and prevent fatal outcomes.
This study presents both strengths and limitations. Our assessment of multiple key outcomes—mortality risk, ICU admission rate, and hospitalization length—in hospitalized COVID-19 patients in Iran contributes valuable data to the global understanding of vaccination efficacy across diverse populations. Additionally, our inclusion of patients who received various non-mRNA vaccines demonstrated the robust protection offered by different vaccine platforms. Our study could have benefited from identifying SARS-CoV-2 variants and measuring antibody levels in patients which are considered study limitations.
Conclusion
Our findings demonstrate that COVID-19 vaccination is associated with significantly improved clinical outcomes in hospitalized COVID-19 patients, including reduced mortality, lower ICU admission rates, shorter hospital stays, and less severe lung damage. These results underscore the importance of vaccination in mitigating severe COVID-19 outcomes.
Supplementary Information
Acknowledgements
We would like to express our gratitude to the authorities of Iran University of Medical Sciences and Firoozgar General Hospital for their support in advancing this study.
Clinical trial number
Not applicable.
Authors’ contributions
B.M. conceptualization & project administration & writing the original draft / A.S. editing the manuscript & data analysis & data curation & preparing tables / M.R. editing the manuscript & project administration & conceptualization & final approval of the manuscript.
Funding
None.
Data availability
Study data can be provided upon reasonable request from corresponding author.
Declarations
Ethics approval and consent to participate
This study is approved by the ethics committee of Iran University of Medical Sciences (Number: IR.IUMS.FMD.REC.1402.123) informed consent to participate in this study was obtained from all subjects or their legal guardians. This study was conducted in accordance with the Declaration of Helsinki.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
References
- 1.Li J, Huang DQ, Zou B, Yang H, Hui WZ, Rui F, et al. Epidemiology of COVID-19: A systematic review and meta-analysis of clinical characteristics, risk factors, and outcomes. J Med Virol. 2021;93(3):1449–58. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Zhu Y, Sharma L, Chang D. Pathophysiology and clinical management of coronavirus disease (COVID-19): a mini-review. Front Immunol. 2023;14:1116131. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Şimşek-Yavuz S. COVID-19: An Update on Epidemiology, Prevention and Treatment, September-2023. Infectious Diseases & Clinical Microbiology. 2023;5(3):165. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.He X, Lau EH, Wu P, Deng X, Wang J, Hao X, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nat Med. 2020;26(5):672–5. [DOI] [PubMed] [Google Scholar]
- 5.Rahman S, Montero MTV, Rowe K, Kirton R, Kunik F Jr. Epidemiology, pathogenesis, clinical presentations, diagnosis and treatment of COVID-19: a review of current evidence. Expert Rev Clin Pharmacol. 2021;14(5):601–21. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Reynolds L, Dewey C, Asfour G, Little M. Vaccine efficacy against SARS-CoV-2 for Pfizer BioNTech, Moderna, and AstraZeneca vaccines: a systematic review. Front Public Health. 2023;11:1229716. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Zsichla L, Müller V. Risk factors of severe COVID-19: a review of host, viral and environmental factors. Viruses. 2023;15(1):175. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Huang Y-Z, Kuan C-C. Vaccination to reduce severe COVID-19 and mortality in COVID-19 patients: a systematic review and meta-analysis. Eur Rev Med Pharmacol Sci. 2022;26(5):1770–6. 10.26355/eurrev_202203_28248. [DOI] [PubMed]
- 9.Rahmani K, Shavaleh R, Forouhi M, Disfani HF, Kamandi M, Oskooi RK, et al. The effectiveness of COVID-19 vaccines in reducing the incidence, hospitalization, and mortality from COVID-19: A systematic review and meta-analysis. Front Public Health. 2022;10: 873596. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Dantas Filho FF, D’Ávila KG, Silva DR. Effect of vaccination on COVID-19 hospitalizations and mortality. J Bras Pneumol. 2023;49(4):e20230254. 10.36416/1806-3756/e20230254. [DOI] [PMC free article] [PubMed]
- 11.Costa GJ, Silva JRd, Silva CCAd, Lima TPFd, Costa MM, Sousa MHO, et al. Risk factors for death and illness severity in vaccinated versus unvaccinated COVID-2019 inpatients: a retrospective cohort study. Jornal Brasileiro de Pneumologia. 2023;49(04):e20230145. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Yıldırım S, Kirakli C, Özdemir Y, Tosun S, Ermin S, Polat G, et al. Impact of vaccination on ICU admissions of hospitalized COVID-19 patients in a country with a heterologous vaccine policy. The Journal of Infection in Developing Countries. 2024;18(04):513–9. [DOI] [PubMed] [Google Scholar]
- 13.Mohammed I, Nauman A, Paul P, Ganesan S, Chen K-H, Jalil SMS, et al. The efficacy and effectiveness of the COVID-19 vaccines in reducing infection, severity, hospitalization, and mortality: a systematic review. Hum Vaccin Immunother. 2022;18(1):2027160. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Lee SW, Ma D, Davoodian A, Ayutyanont N, Werner B. COVID-19 vaccination decreased COVID-19 hospital length of stay, in-hospital death, and increased home discharge. Preventive Medicine Reports. 2023;32: 102152. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Samara AA, Boutlas S, Janho MB, Gourgoulianis KI, Sotiriou S. COVID-19 severity and mortality after vaccination against SARS-CoV-2 in Central Greece. Journal of Personalized Medicine. 2022;12(9):1423. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Wu N, Joyal-Desmarais K, Ribeiro PA, Vieira AM, Stojanovic J, Sanuade C, et al. Long-term effectiveness of COVID-19 vaccines against infections, hospitalisations, and mortality in adults: findings from a rapid living systematic evidence synthesis and meta-analysis up to December, 2022. Lancet Respir Med. 2023;11(5):439–52. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Valeanu L, Andrei S, Morosanu B, Longrois D, Bubenek-Turconi S-I, Collaborative C-R. The COVID-19 vaccination coverage in ICU patients with severe COVID-19 infection in a country with low vaccination coverage—a national retrospective analysis. J Clin Med. 2023;12(5):1749. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.van Diepen S, McAlister FA, Chu LM, Youngson E, Kaul P, Kadri SS. Association between vaccination status and outcomes in patients admitted to the ICU with COVID-19. Crit Care Med. 2023;51(9):1201–9. [DOI] [PubMed] [Google Scholar]
- 19.Barek MA, Aziz MA, Islam MS. Impact of age, sex, comorbidities and clinical symptoms on the severity of COVID-19 cases: A meta-analysis with 55 studies and 10014 cases. Heliyon. 2020;6(12):e05684. 10.1016/j.heliyon.2020.e05684. [DOI] [PMC free article] [PubMed]
- 20.Bigdelou B, Sepand MR, Najafikhoshnoo S, Negrete JAT, Sharaf M, Ho JQ, et al. COVID-19 and preexisting comorbidities: risks, synergies, and clinical outcomes. Front Immunol. 2022;13: 890517. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Wichaidit M, Nopsopon T, Sunan K, Phutrakool P, Ruchikachorn P, Wanvarie D, et al. Breakthrough infections, hospital admissions, and mortality after major COVID-19 vaccination profiles: A prospective cohort study. Lancet Reg Health Southeast Asia. 2023;8:100106. 10.1016/j.lansea.2022.100106. [DOI] [PMC free article] [PubMed]
- 22.Firouzabadi N, Ghasemiyeh P, Moradishooli F, Mohammadi-Samani S. Update on the effectiveness of COVID-19 vaccines on different variants of SARS-CoV-2. Int Immunopharmacol. 2023;117: 109968. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Mohraz M, Vahdat K, Ghamari S-H, Abbasi-Kangevari M, Ghasemi E, Ghabdian Y, et al. Efficacy and safety of an inactivated virus-particle vaccine for SARS-CoV-2, BIV1-CovIran: randomised, placebo controlled, double blind, multicentre, phase 3 clinical trial. BMJ. 2023;382:e070464. 10.1136/bmj-2023-070464. Erratum in: BMJ. 2023;382:2193. 10.1136/bmj.p2193. [DOI] [PMC free article] [PubMed]
- 24.Tabarsi P, Mamishi S, Anjidani N, Shahpari R, Kafi H, Fallah N, et al. Comparative immunogenicity and safety of SpikoGen®, a recombinant SARS-CoV-2 spike protein vaccine in children and young adults: an immuno-bridging clinical trial. Int Immunopharmacol. 2024;127: 111436. [DOI] [PubMed] [Google Scholar]
- 25.Ghiasi N, Valizadeh R, Arabsorkhi M, Hoseyni TS, Esfandiari K, Sadighpour T, et al. Efficacy and side effects of Sputnik V, Sinopharm and Astra Zeneca vaccines to stop COVID-19 a review and discussion. Immunopathologia Persa. 2021;7(2):e31-e. [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
Study data can be provided upon reasonable request from corresponding author.