ORIGINAL ARTICLE

FACTORS ASSOCIATED WITH THE CLINICAL OUTCOMES OF OLDER ADULTS WITH COVID-19 ACCORDING TO VACCINE AVAILABILITY: AN OBSERVATIONAL STUDY

Luiz Hiroshi Inoue1, Wanessa Cristina Baccon2, Francielle Renata Danielli Martins3, Guilherme Kenzo Acutu4, Márcia Lorena Alves dos Santos5, Giovana Alves Santos Rodrigues6, Maria Aparecida Salci7, Lígia Carreira8

1 Universidade Estadual de Maringá, Maringá, PR, Brazil. ORCID: 0000-0002-7226-9661. E-mail: lhinoue17@gmail.com.

2 Universidade Estadual de Maringá, Maringá, PR, Brazil. ORCID: 0000-0001-9750-3576. E-mail: wanessabaccon@hotmail.com.

3 Universidade Estadual de Maringá, Maringá, PR, Brazil. ORCID: 0000-0002-8578-9615. E-mail: franrenata.martins@gmail.com.

4 Universidade Estadual de Maringá, Maringá, PR, Brazil. ORCID: 0000-0002-5940-8110. E-mail: guilherme_kenzo_@hotmail.com.

5 Universidade Estadual de Maringá, Maringá, PR, Brazil. ORCID: 0000-0002-1098-1944. E-mail: alves.mlorena@gmail.com.

6 Universidade Estadual de Maringá, Maringá, PR, Brazil. ORCID: 0000-0002-5586-4688. E-mail: giovanaalvessantos@yahoo.com.

7 Universidade Estadual de Maringá, Maringá, PR, Brazil. ORCID: 0000-0002-6386-1962. E-mail: msalci@uem.br.

8 Universidade Estadual de Maringá, Maringá, PR, Brazil. ORCID: 0000-0003-3891-4222. E-mail: ligiacarreira.uem@gmail.com.

ABSTRACT

Objective: To identify the association of sociodemographic and clinical factors with the clinical outcomes of older adults hospitalized in intensive care units (ICUs) in the state of Paraná, according to the availability of COVID-19 vaccination. Method: Analytical observational, population-based study using secondary data from older adults hospitalized with COVID-19 in ICUs. Conditional odds ratios were estimated, homogeneity between strata was assessed using the Breslow-Day test (5%), and conditional independence was evaluated using the Mantel-Haenszel test, with estimation of the common odds ratio. Results: The following were associated with higher odds of hospital discharge: age group (OR = 1.97), female sex (OR = 1.20), and White race/color (OR = 1.22). Older adults with ≤ 9 years of schooling (OR = 0.63), risk factors (OR = 0.69), diabetes (OR = 0.82), immunodeficiency (OR = 0.57), liver disease (OR = 0.50), hematological disease (OR = 0.56), chronic lung disease (OR = 0.61), and use of ventilatory support (OR = 0.30) had lower odds of hospital discharge. Conclusion: Vaccination was associated with higher odds of hospital discharge according to age group, sex, White skin color, and higher educational level. Comorbidities such as diabetes mellitus, immunodeficiency, liver disease, chronic lung disease, and the use of ventilatory support reduced this likelihood.

Descriptors: COVID-19; Public Health Nursing; Immunization Schedules; Health of the Elderly; Intensive Care Units.

What is already known:

• COVID-19 has a high case-fatality rate among older adults, significantly worsened by the presence of preexisting comorbidities.

• COVID-19 vaccination has been proven effective in reducing hospitalizations, severe complications, and deaths in the older population.

• Clinical outcomes of ICU patients with COVID-19 changed throughout the pandemic, following epidemiological changes and adjustments in clinical management.

What this article adds:

• Vaccine availability reduced overall mortality, but comorbidities such as liver disease and immunodeficiency remained associated with lower odds of discharge.

• Sociodemographic factors, specifically higher educational level and White skin color, were determinants of increased survival chances in the ICU.

• The magnitude of the association between specific comorbidities (e.g., kidney disease, heart disease, and neurological disease) and ICU outcomes (discharge/death) varied across periods, indicating temporal heterogeneity in clinical vulnerabilities among older adults.

INTRODUCTION

COVID-19, declared a pandemic on March 11, 2020(1), remains a public health problem. Although the world has resumed a certain level of normality after the critical period, the disease has continued to be one of the leading causes of death from respiratory infections, especially among older adults and children, accounting for more than 7 million deaths(2). In Brazil, more than 716,000 deaths have been recorded, with particular concern for the first months of 2025, during which more than 130,000 cases and hundreds of deaths were reported(1).

Infection with the virus that causes COVID-19 may pose a high health risk for individuals of advanced age and those with preexisting comorbidities, increasing the likelihood of hospitalization, complications, and death in this population(3). In the United States of America (USA), a study found that adults aged over 65 years accounted for 53% of admissions to Intensive Care Units (ICUs) and 80% of deaths, with a linear increase in mortality as age advanced(4). In Brazil, a similar study identified an increase of more than 70% in the risk of death among older adults admitted to ICUs and diagnosed with COVID-19(5).

The proportion of deaths among older adults due to COVID-19 in Brazil reached 76% between February and September 2020(6). Disease severity and lethality may be related to the presence of comorbidities such as arterial hypertension, diabetes mellitus, respiratory diseases, cardiovascular diseases, and obesity, which become risk factors for individuals infected with COVID-19(7).

Beyond individual risk, the hospitalization of older adults in ICUs exposed care-related and organizational challenges: severe clinical conditions requiring ventilatory and hemodynamic support, greater care complexity, and, during periods of high transmission, pressure on beds and healthcare teams, with direct repercussions for resource management and clinical decision-making processes(8).

Recent studies have documented that capacity overload in scarcity scenarios is associated with changes in decisions related to ICU eligibility, raising ethical and care-related implications(9,10). At the same time, even when the acute outcome is favorable, relevant consequences may persist after critical illness, including functional impairment and the need for post-discharge follow-up, encompassing components of “Long COVID” with physical, cognitive, and psychosocial effects(11). Among older adults, the literature emphasizes the importance of evaluating outcomes beyond hospital discharge, incorporating functionality and quality of life as central dimensions of care(12).

As a strategy to reduce disease progression, vaccines were developed to prevent complications and death. With the start of vaccination in Brazil in January 2021, older adults were included in priority groups, considering their vulnerabilities and greater susceptibility to infection(13). According to recommendations from the Ministry of Health, the vaccination schedule prioritized individuals aged 80 years or older and residents of Long-Term Care Facilities (LTCFs)(14). Two months after the start of vaccination, the first positive results were observed, with a significant reduction in the percentage of deaths among older adults in these institutions(15).

Studies published in 2025 support that vaccination and booster doses reduce hospitalizations and severe outcomes, although evidence indicates waning protection over time, reinforcing the need for monitoring according to time since the last dose and individual risk profile(16,17). Additionally, studies involving hospitalized patients have reported an association between vaccination and lower risk of ICU admission, reduced mortality, and shorter length of hospital stay(18,19).

Despite advances in understanding the impact of vaccination, knowledge about clinical outcomes and morbidity and mortality among older adults hospitalized in ICUs, specifically in relation to vaccination status, remains limited. Although existing studies include older adults, detailed analyses focused exclusively on this group are scarce.

In this context, it is essential to understand how sociodemographic and clinical factors interact with vaccination status to influence the clinical course of older adults with COVID-19 hospitalized in ICUs. Conducting an association study is justified by the need to identify factors related to more severe outcomes, such as death, even after the introduction of vaccination. Such evidence may contribute to the development of more effective public policies and care strategies, as well as to the monitoring of vaccination effectiveness in vulnerable populations.

Considering the increased susceptibility of older adults to complications, ICU admission, and death due to COVID-19, as well as the effectiveness of vaccination in reducing hospitalizations, the objective of this study was to identify the association of sociodemographic and clinical factors with the clinical outcomes of older adults hospitalized in ICUs in the state of Paraná, according to the availability of COVID-19 vaccination.

METHOD

This was a retrospective analytical observational study based on secondary data, linked to the cohort “Longitudinal Follow-up of Adults and Older Adults Discharged from Hospitalization due to COVID-19,” developed through a partnership between the State University of Maringá (UEM) and the Paraná State Health Department (SESA/PR), with financial support from the National Council for Scientific and Technological Development (CNPq). The observational design was adopted because it is appropriate for investigating associations between sociodemographic and clinical characteristics and ICU hospitalization outcomes among older adults with COVID-19, without direct intervention on individuals.

The use of statewide secondary data enabled the inclusion of a large population contingent, increasing the statistical power of the analyses. The analytical approach was based on estimating odds ratios, stratified according to periods of COVID-19 vaccine availability, in order to incorporate relevant temporal variations in the epidemiological and healthcare context. The study was conducted in the state of Paraná, which comprises 399 municipalities and an estimated population of 11,675,661 inhabitants, of whom 1,927,286 are older adults, according to DataSUS projections for 2020(20). The analyses followed the recommendations of the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guideline(21).

Sociodemographic and clinical data were obtained from the Influenza Epidemiological Surveillance Information System (SIVEP-Gripe) database, maintained by the Health Surveillance Secretariat of the Ministry of Health, updated on November 7, 2022. Public-domain data from compulsory notification forms for Severe Acute Respiratory Syndrome (SARS) were used; these forms do not allow individual patient identification(22). The study period ranged from March 16, 2020, to March 15, 2022.

The study population comprised individuals aged 60 years or older, residing in Paraná, with a final diagnosis of COVID-19, hospitalized and admitted to ICUs within the state. Records with missing information for residence area, education level, and race/color were excluded, as well as deaths due to causes unrelated to COVID-19. Of the 23,297 initial records, the final sample included 11,918 older adults after systematic application of the exclusion criteria, ensuring the robustness of the results.

The explanatory (independent) variables included: age group (60–74 years; ≥75 years), sex (male; female), race/color (White; Black/Asian/Indigenous), education (≤9 years; >9 years), area of residence (urban/peri-urban; rural), use of influenza antivirals, influenza vaccination, presence of risk factors/comorbidities, and use of ventilatory support. Specific comorbidities (diabetes mellitus, immunodeficiencies, chronic liver, hematological, cardiovascular, neurological, or kidney diseases, asthma, and chronic lung diseases) were also analyzed individually. The primary outcome (response variable) was ICU hospitalization outcome, categorized as hospital discharge (recovery) or death.

The stratifying variable was temporal vaccine availability, categorized into three periods: Unavailable: March 16, 2020, to January 18, 2021 (pre-vaccination); Partially available: January 19, 2021, to June 3, 2021 (initial phase and gradual rollout); and Available: June 4, 2021, to March 15, 2022 (full vaccination schedule available for the age group).

For each explanatory variable, conditional odds ratios were estimated within each vaccine availability stratum. Homogeneity of the odds ratios across strata was assessed using the Breslow–Day test (5% significance level). When homogeneity was confirmed, the Mantel-Haenszel test was applied to verify the common association across periods. In cases of heterogeneity (rejection of the Breslow–Day hypothesis), the adjusted Breslow–Day test was used for post-hoc comparisons.

Data were processed using R software (version 4.3.2), with the magrittr, dplyr, and tidyverse packages for data manipulation, and DescTools, vcd, and epiDisplay for stratified 2×2 analyses.

The study was approved by the Research Ethics Committee involving Human Beings (Opinion No. 4,214,589; CAAE: 34787020.0.3001.5225), in accordance with Resolutions 466/2012 and 510/2016 of the National Health Council. As public-domain data without individual identification were used, the requirement for informed consent was waived.

RESULTS

The analyzed data comprise records from a sample of 11,918 older adults hospitalized and admitted to ICUs due to COVID-19 in the state of Paraná, distributed across three periods of vaccine availability: unavailable (n = 4,486), partially available (n = 4,638), and available (n = 2,794).

Across the three periods analyzed, most older adults admitted to ICUs were aged 60 to 74 years, were male, had White skin color, and lived in urban/peri-urban areas within the same municipality where hospitalization occurred. Regarding education, the group with more than nine years of schooling predominated. Most of the study population did not use antivirals, had not received influenza vaccination, and presented at least one risk factor.

With respect to COVID-19 vaccination, it was observed that during the partially available period, a minority of older adults admitted to ICUs had been vaccinated. In contrast, during the available period, most older adults admitted to ICUs had already received the vaccine, as detailed in Table 1.

Table 1 – Sociodemographic and clinical characteristics of older adults hospitalized in ICUs due to COVID-19 in the state of Paraná, according to COVID-19 vaccination status (n = 11,918). Maringá, PR, Brazil, 2022

Source: prepared by the authors, 2025.

Table 2 presents the association analysis between sociodemographic and clinical variables and the outcomes of older adults hospitalized in ICUs due to COVID-19, stratified by vaccination periods, based on the Breslow-Day test.

The Breslow-Day test assessed the homogeneity of odds ratios (ORs) across the periods. Significant differences (p < 0.05) were observed for age group, cardiovascular disease, neurological disease, and kidney disease, indicating that the magnitude of the association between these variables and the outcome varied according to the vaccination period.

During the period when the vaccine was unavailable, older adults aged 60 to 74 years had 86% higher odds of hospital discharge compared with those aged 75 years or older. This probability increased to 97% during the partially available period and decreased to 24% during the period when the vaccine was available (p < 0.05).

Regarding older adults with cardiovascular disease, it was observed that while the vaccine was unavailable, there was no significant association between the condition and the likelihood of hospital discharge (p > 0.05). During the partially available period, older adults with cardiovascular disease had 14% lower odds of discharge compared with those without this comorbidity (p < 0.05). In the period when the vaccine was available, this reduction in the likelihood of discharge increased to 30% (p < 0.05).

Older adults with neurological diseases had 37% lower odds of hospital discharge compared with those without this condition during the period of vaccine unavailability. In the partially available period, this reduction was 27% (p < 0.05). When the vaccine was available, the reduction in the likelihood of discharge reached 54% (p < 0.05).

Among older adults with kidney disease, a 37% reduction in the likelihood of hospital discharge was observed when the vaccine was not yet available. This reduction was 28% during the partially available phase (p < 0.05). However, in the period when the vaccine was available, the association was no longer statistically significant (p > 0.05).

Table 2 – Factors associated with the outcome of elderly individuals hospitalized in ICUs for Covid-19 in the state of Paraná according to vaccination status, Breslow-Day test (n=11,918). Maringá, PR, Brazil, 2022

Source: prepared by the authors, 2025.

Table 3 presents the variables for which the Breslow–Day test indicated homogeneity of the odds ratios across the vaccine availability periods, allowing the calculation of the Mantel–Haenszel common odds ratio. This estimate was statistically significant for sex, race/skin color, education, presence of risk factors, diabetes, immunodeficiency, liver disease, chronic lung disease, and use of ventilatory support.

Older women and older adults of White race/skin color had 20% and 22% higher odds of hospital discharge, respectively, compared with older men and those of Black, Asian, or Indigenous race/skin color. It is important to note that sex and race/skin color were analyzed separately in relation to the outcome.

Regarding education, older adults with fewer than 9 years of schooling had 27% lower odds of discharge compared with those with more than 9 years of education. No statistically significant differences in the odds of discharge were observed for the following variables: area of residence (p = 0.24), residence in the same municipality as the hospitalization (p = 0.68), use of antivirals for influenza (p = 0.99), influenza vaccination (p = 0.73), and diagnosis of asthma (p = 0.79).

Older adults with preexisting risk factors had 31% lower odds of discharge compared with those without any risk factors. However, the number of deaths among older adults with at least one risk factor during the period when the vaccine was unavailable was approximately 60% higher than during the period when the vaccine was available.

Among older adults admitted to the ICU with preexisting comorbidities such as diabetes, immunodeficiency, liver disease, hematologic disease, and chronic lung disease, the odds of discharge were lower compared with those without these conditions. The most pronounced effects were observed among those with liver disease, hematologic disease, and immunodeficiency, who had 50%, 44%, and 43% lower odds of discharge, respectively. Older adults with diabetes and chronic lung disease showed 18% and 39% lower odds of discharge, respectively. Finally, older adults who required ventilatory support had 70% lower odds of discharge compared with those who did not use this intervention.

Table 3 – Factors associated with the outcome of elderly individuals hospitalized in ICUs for Covid-19 in the state of Paraná according to Covid-19 vaccination status, Breslow-Day, and Mantel-Haenszel tests (n=11,918). Maringá, PR, Brazil, 2022

Source: prepared by the authors, 2025.

DISCUSSION

The results highlight the complex interaction between the availability of COVID-19 vaccines, hospital outcomes among older adults, demographic factors, and preexisting comorbidities. The variation observed across the pre-vaccination, implementation, and full availability periods is consistent with scientific evidence demonstrating the benefits of immunization in reducing morbidity and mortality, particularly among vulnerable populations(15,23–24).

The rapid development of vaccines against SARS-CoV-2 and their implementation through mass vaccination campaigns proved to be highly successful strategies for mitigating the effects of the pandemic(23). Findings from a study conducted in Washington, USA, showed a significant reduction in hospitalizations among individuals aged 65 years or older after vaccine administration; six weeks after the start of vaccination, a substantial decrease in the odds of death was observed in this group(24).

Additionally, a meta-analysis showed that, among older adults, receiving a higher number of doses was associated with a lower risk of infection, hospitalization, and death compared with those who received fewer doses(25). These findings reinforce the importance of maintaining booster schedules in this population. Another systematic review found that a complete vaccination regimen provided up to 75% protection against symptomatic infection, 63% to 80% protection against hospitalization, and 65% to 81% protection against severe disease, regardless of sex and age(26). As reported in the literature, although older adults present a naturally reduced immune response, booster vaccination is associated with increased antibody production and improved overall immune capacity(25,27).

An important finding of this study is that, when the vaccine was available, the likelihood of discharge remained higher among individuals aged 60 to 74 years compared with those aged 75 years or older; however, the disparity between these age groups decreased to 24%. This attenuation may be associated with the Brazilian immunization plan, which prioritized the first doses for individuals aged 80 years or older(14). Evidence supports the notion that vaccination remains a vital tool for protecting this population, overcoming initial concerns regarding the magnitude of the immune response(28–29).

Due to the high lethality rate among older adults residing in long-term care facilities (LTCFs), immunization of this group was prioritized in several countries(14). COVID-19 proved particularly harmful to institutionalized individuals because of a combination of biological vulnerabilities and structural characteristics of these facilities, such as shared bedrooms and common areas, which hinder social distancing and transmission control(30). In this context, it is essential to implement complementary measures alongside vaccination to reduce severe outcomes in these settings(14,30,31).

Regarding sociodemographic factors, higher odds of hospital discharge were associated with White skin color, higher education level, younger age within the older age group, and female sex. Concerning race/skin color and education, studies conducted in the United States corroborate that older adults with lower educational attainment and those self-identified as Black have higher odds of unfavorable outcomes, reflecting structural inequalities in access to health care(31).

Finally, aging is associated with a decline in multiple cellular groups, resulting in weaker immune responses compared with younger populations(23). The immune response capacity of older adults is challenged by immunosenescence. Although vaccines may present lower biological efficacy in this group, the literature indicates that even a single vaccine dose was associated with an 85% reduction in the risk of death in this population, confirming the positive clinical impact of the intervention(28).

Regarding sex, a study conducted in Turkey on vaccine effectiveness identified differences between older men and women, similar to those observed in the present study. Administration of the second dose of the Sinovac vaccine resulted in a substantial reduction in ICU admissions among older women. The study also highlighted that older adults with more than one preexisting comorbidity were less likely to experience favorable outcomes(32).

Concerning clinical factors, this study found poorer discharge outcomes among older adults with chronic diseases, who have a higher intrinsic risk of hospitalization and mortality(13,33). A study conducted in Italy showed that the incidence of COVID-19 among individuals with chronic diseases increased from 4.1% in 2020 to 7.3% in 2021. In this context, the probability of hospitalization and death increased progressively among individuals with two or more comorbidities compared with those with only one(34).

Furthermore, evidence indicates that individuals with severe and debilitating conditions, such as neoplasms, showed lower vaccine acceptance compared with those with less severe conditions, such as isolated hypertension. Vaccination rates were also proportionally lower among individuals with chronic conditions compared with the general population(34–35).

The results of this study indicated unfavorable outcomes particularly among older adults with liver disease, hematologic disorders, immunodeficiency, and diabetes mellitus. Prospective studies show that liver injury caused by SARS-CoV-2 occurs through ACE2 receptors present in hepatocytes and cholangiocytes. In addition to reducing protein synthesis capacity, infection compromises coagulation factors and metabolic reserve, which interact synergistically with the prothrombotic state characteristic of COVID-19(36).

Older patients with hematologic disorders also constitute a high-risk group. This is due to immunosuppression inherent to the disease itself and to cytotoxic treatments, resulting in lymphocyte depletion and impaired viral clearance(15,23,25). In addition, the virus infects monocytes and endothelial cells, triggering a cytokine storm, lymphopenia, and activation of the coagulation cascade, leading to thrombosis and disseminated intravascular coagulation in severe cases—complications that are particularly deleterious for an already immunocompromised population(37).

The literature reinforces that older adults with hematologic diseases experience a more severe clinical course. A multicenter analysis involving 569 patients reported an overall mortality rate of 29.3%, with individuals aged over 70 years and those with associated comorbidities presenting a higher probability of death(38). This vulnerability requires rigorous clinical management strategies, including continuous monitoring of hematological parameters and intensive supportive care plans(39,40).

Regarding diabetes mellitus, the increased risk of death is substantial. Pathophysiological mechanisms include chronic hyperglycemia, which impairs immune function and promotes systemic inflammation. In addition, SARS-CoV-2 may directly affect pancreatic beta cells, worsening glycemic control and contributing to organ damage(41). However, analyses conducted in Brazil demonstrated that fully vaccinated individuals with diabetes had significantly lower rates of hospital mortality and ICU admission compared with unvaccinated individuals, supporting our findings(42).

Finally, regarding immunodeficiency, data from the World Health Organization indicate that immunocompromised patients (including those with cancer, transplant recipients, and people living with HIV) remain at high risk of death despite therapeutic advances(43). Although vaccination provides beneficial effects, immunosuppression may attenuate the expected immune response, making the maintenance of additional protective measures essential for these patients.

Regarding the need for mechanical ventilation during ICU hospitalization, a comparative study involving 3,293 fully vaccinated, partially vaccinated, and unvaccinated individuals found that unvaccinated patients were more likely to require invasive ventilatory support, vasopressor use, and longer ICU stays(44). These data corroborate the findings of the present study, which showed a substantial reduction in ICU admissions during the period of full vaccine availability compared with the periods of unavailability or initial implementation.

Overall, COVID-19 vaccination had a significant impact on reducing mortality among individuals with chronic cardiac, renal, respiratory diseases, and diabetes, highlighting the role of immunization in protecting these vulnerable groups(34). Evidence indicates that vaccinated patients, even those with comorbidities, had a lower risk of death compared with unvaccinated individuals, positioning vaccination as a crucial protective factor against progression to critical illness(45,46).

The findings emphasize the value of continuous booster vaccination among older adults. Given the increased risk of severe disease, maintaining high levels of immunity through regular booster doses is essential to protect this population(46). In addition, although unfavorable socioeconomic conditions act as risk indicators, studies suggest that the direct impact of chronic diseases on COVID-19 mortality is more predictive than the indirect effect of poverty(47). This reinforces that comorbidities remain the primary determinants of unfavorable clinical outcomes.

This study provides evidence to support health managers in formulating data-driven public policies, allowing care strategies to be aligned with the actual characteristics observed. The stratified analysis organized according to the vaccine availability timeline made it possible to demonstrate the association between access to vaccination and the mitigation of severe cases.

The limitations of this study are primarily related to its retrospective observational design and the use of secondary data. These factors limit causal inference and may introduce information bias due to potential incompleteness or inconsistencies in record completion. Additionally, the analysis was based on stratified associations not simultaneously adjusted for multiple confounding factors, which may result in residual confounding.

It is also important to consider that restricting the analysis to ICU patients may have concentrated the sample among individuals with inherently more severe conditions and a higher burden of comorbidities. Finally, the regional nature of the study limits the generalizability of the findings to other geographic contexts.

Despite these limitations, the findings provide relevant insights into the clinical course of older adults in intensive care. For the advancement of this research field, future studies should prioritize the incorporation of individualized vaccination data and the use of multivariate analytical approaches. Prospective studies including clinical frailty measures, severity biomarkers, and identification of viral variants are also recommended, enabling a broader analysis of the interaction between vaccination and the physiological reserve of older adults.

CONCLUSION

The findings of this study demonstrate that, among older adults admitted to ICUs due to COVID-19 in the state of Paraná, sociodemographic factors such as age between 60 and 74 years, female sex, White race/skin color, and higher educational level were associated with greater odds of hospital discharge. In contrast, chronic conditions—such as diabetes mellitus, immunodeficiency, liver disease, and chronic lung diseases—and, particularly, the need for ventilatory support were identified as markers of increased risk of death.

Immunization proved to be a key factor in reducing mortality, although older adults with multiple comorbidities remained more vulnerable. These results reinforce the importance of public vaccination policies targeting priority groups and the need for complementary care strategies for individuals with greater clinical frailty.

However, the interpretation of these findings should consider limitations inherent to the retrospective design and the use of secondary data, which may present incompleteness or underreporting. In addition, the exclusive inclusion of ICU patients limits the generalizability of the results to older adults treated in general wards or outpatient follow-up.

Future research should advance the integration of databases to incorporate detailed individual vaccination histories, as well as specific clinical variables such as laboratory markers and frailty indicators. These advances will enable more robust multivariate analytical models and the assessment of complex interactions between comorbidities and ventilatory support. Furthermore, multicenter studies with post-discharge follow-up are essential to evaluate long-term outcomes, such as functional status and late mortality.

Finally, this study highlights the strategic role of Primary Health Care and Nursing in promoting immunization and addressing vaccine hesitancy. The findings provide evidence to support the improvement of public health policies, reaffirming vaccination as an essential measure for protection and favorable clinical outcomes among older adults hospitalized with COVID-19.

CONFLICT OF INTEREST

The authors declare no conflict of interest.

FUNDING

This study was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brazil (CAPES) – Financing Code 001; the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) through Circular Letter No. 14/2020-GAB/PR/CAPES, dated March 30, 2020; Public Notice No. 07/2020 – Universal Call from the Ministry of Science, Technology, Innovations and Communications (MCTIC); the National Council for Scientific and Technological Development (CNPq); the National Fund for Scientific and Technological Development (FNDCT); the Ministry of Health (MS)/Secretariat of Science, Technology, Innovation and Strategic Health Inputs (SCTIE)/Department of Science and Technology (Decit). Process: 402882/2020-2.

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Submission: 08-Dec-2025

Approved: 08-Feb-2026

Editors:

Rosimere Ferreira Santana (ORCID: 0000-0002-4593-3715)

Geilsa Soraia Cavalcanti Valente (ORCID: 0000-0003-4488-4912)

Alessandra Conceição Leite Funchal Camacho (ORCID: 0000-0001-6600-6630)

Corresponding author: Luiz Hiroshi Inoue (lhinoue17@gmail.com)

Publisher:

Escola de Enfermagem Aurora de Afonso Costa – UFF

Rua Dr. Celestino, 74 – Centro, CEP: 24020-091 – Niterói, RJ, Brazil

Journal email: objn.cme@id.uff.br