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Adults Hospitalized With Coronavirus Disease 2019 (COVID-19)—United States, March–June and October–December 2020: Implications for the Potential Effects of COVID-19 Tier-1 Vaccination on Future Hospitalizations and Outcomes

Abstract Background Because of the increased risk for severe coronavirus disease 2019 (COVID-19), the Advisory Committee on Immunization Practices (ACIP) initially prioritized COVID-19 vaccination for persons in long-term care facilities (LTCF), persons aged ≥65 years, and persons aged 16–64 years with high-risk medical conditions when there is limited vaccine supply. We compared characteristics and severe outcomes of hospitalized patients with COVID-19 in the United States between early and later in the pandemic categorized by groups at higher risk of severe COVID-19. Methods Observational study of sampled patients aged ≥18 years who tested positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and admitted to one of 14 academic hospitals in the United States during March–June and October–December 2020. Demographic and clinical information were gathered from electronic health record data. Results Among 647 patients, 91% met ≥1 of the following risk factors for severe COVID-19 [91% March-June (n = 434); 90% October–December (n = 213)]; 19% were LTCF residents, 45% were aged ≥65-years, and 84% had ≥1 high-risk condition. The proportion of patients who resided in a LTCF declined significantly (25% vs 6%) from early to later pandemic periods. Compared with patients at lower risk for severe COVID-19, in-hospital mortality was higher among patients at high risk for severe COVID-19 (20% vs 7%); these differences were consistently observed between March–June and October–December. Conclusions Most adults hospitalized with COVID-19 were those recommended to be prioritized for vaccination based on risk for developing severe COVID-19. These findings highlight the continued urgency to vaccinate patients at high risk for severe COVID-19 and monitor vaccination impact on hospitalizations and outcomes.


Introduction
The Advisory Committee on Immunization Practices (ACIP) recommended a phased approach to coronavirus disease 2019 (COVID-19) vaccination, given the initial limited supply of vaccine. To protect patients at increased risk for SARS-COV-2 infection or severe COVID-19, ACIP recommended prioritizing vaccination to long-term care facility (LTCF) residents, persons aged ≥75 years, persons aged 65-74 years, and persons aged 16-64 years with high-risk medical conditions, along with frontline healthcare personnel and other essential workers [1]. The increased risk for severe disease with increasing age is well established [2]. Through the week ending January 2, 2021, the cumulative COVID-19associated hospitalization rate among persons aged >65 was 1,122 per 100,000 population, double the rate among those aged 50-64 years (526 per 100,000) [2]. Previous studies have also shown that hospitalization rates are higher among those with underlying conditions such as obesity, diabetes, and chronic kidney disease [3][4][5][6]. Evidence from SARS-CoV-2 vaccine trials suggests that vaccination may provide the greatest protection against severe COVID-19 illness [7,8]. Thus, prioritizing groups at higher risk of severe illness from COVID-19 for vaccination is important for reducing hospitalizations and deaths.
Using data from adults hospitalized for COVID-19 at 14 academic medical centers during two periods of the pandemic (March-June and October-December 2020), our study had two objectives. First, we assessed whether demographic and baseline health characteristics among patients differed between early (March-June) and later (October-December) periods as overall characteristics of adults diagnosed with SARS-CoV-2 has changed markedly over time in the US with a shift toward increasing infections within younger age groups whereas classification of high-risk conditions for hospitalization in the US were characterized early A c c e p t e d M a n u s c r i p t 6 during the pandemic [5,9]. Second, we assessed severe outcomes categorized by groups at higher risk of severe COVID-19 and examined whether outcomes for patients with COVID-19 improved over time.

Methods
In a prospective study at 14 U.S. academic health centers in the Influenza and other Viruses in the acutely ill (IVY) Network, which performs epidemiological and vaccine effectiveness evaluations on influenza and SARS-CoV-2, hospitalized patients aged ≥18 years who had a positive reverse transcription-polymerase chain reaction (RT-PCR) test result for SARS-CoV-2 were sampled at two time points [10]. Sites participating in the IVY Network include:   Table 1], and clinical outcomes using a standardized case report form.
High-risk medical conditions associated with increased risk for severe COVID-19 were defined by CDC as cancer; chronic kidney disease; chronic obstructive pulmonary disease (COPD); heart conditions (e.g., heart failure, coronary artery disease, or cardiomyopathies); immunocompromised state from solid organ transplant; obesity (body mass index [BMI] ≥30 kg/m 2 ); sickle cell disease; smoking; diabetes mellitus; and pregnancy [1]. Criteria defined by ACIP to prioritize those at increased risk for severe COVID-19 were LTCF residents, persons aged ≥75 years, persons aged 65-74 years, and persons aged 16-64 years with high-risk medical conditions [1]. Hospitalized patients were followed for up to 30 days after admission to record severe in-hospital outcomes. Severe outcomes were defined as receipt of noninvasive ventilation including bilevel positive pressure ventilation or continuous positive pressure ventilation, receipt of invasive mechanical ventilation, receipt of vasopressor support, receipt of dialysis/renal replacement therapy, receipt of extracorporeal membrane oxygenation, incident stroke, venous thromboembolic event (deep vein thrombosis or pulmonary embolism), or death. Missing height or weight information (needed to calculate BMI for obesity determination) were not imputed, and patients with missing weight or height A c c e p t e d M a n u s c r i p t 8 were excluded from the obesity analysis. Detailed information on employment history, including healthcare-related work or other essential work, was not available for either time period.
Characteristics of patients during the two time periods, as well as of those meeting one or more versus no criteria for increased risk of severe COVID-19, were compared using Wilcoxon rank-sum testing for continuous variables and chi-squared or Fisher's exact test for categorical variables. Significance was defined as p<0.05. Analyses were performed using SAS Version 9.4 (Cary, North Carolina).

The study was reviewed by Centers for Disease Control and Prevention (CDC) and was
conducted consistent with applicable federal law and CDC policy. 1 A c c e p t e d M a n u s c r i p t 9 and COPD (10%). Participants had none (9%), one (47%), two (32%) or all three (12%) criteria for increased risk for severe COVID-19.

Among
Compared with March-June, a higher percentage of patients hospitalized during October-December were non-Hispanic White (63% versus 28%; 15% versus 25% were non-Hispanic Black; 19% versus 35% were Hispanic) and resided in the community before admission (94% versus 71%; 6% versus 25% resided in a LTCF) [ Table 1]. The distribution of age and sex were similar between periods. The percentage of patients with a medical condition that increased the risk for severe COVID-19 was generally similar in the March-June and October-December cohorts. However, obesity was more prevalent in the October-December cohort (58% versus 43%). Excluding obesity, a prevalent condition in the study population, 80% (333 of 418) and 74% (155 of 210) during the early and later period, respectively, met the criteria for increased risk for severe COVID-19.
Overall, in-hospital mortality was 18% (n=117), similar between early and later periods (18% versus 19%, respectively) and highest among persons aged ≥75 years (35%) [Supplementary  interventions and improved mitigation efforts following multiple LTCF outbreaks early in the pandemic, such as serial facility-wide testing requirements in nursing homes, and a subsequent reduction of infection in this population [13,14]. The higher proportion of hospitalized patients from the community during October-December might be a result of increasing COVID-19 cases among younger age groups in the community [9]. Thus, while ensuring high vaccination rates in those at increased risk of severe COVID-19 is important, rapidly expanding access to vaccination in the community is urgently needed once there is wider availability of vaccine. As this network of health centers continues to conduct active post-vaccination surveillance for vaccine effectiveness against severe COVID-19, these data provide a useful baseline at each of the network sites to monitor changes in epidemiology.
Some limitations must be considered. First, distribution of patients by site differed between the early and late cohort with higher cases from New York and Massachusetts hospitals in the Spring and Tennessee in the Fall [Supplementary Table 3]. This could have influenced some of the differences that were observed between cohorts such as differences in race/ethnicity between periods. In the New York and Massachusetts sites, which represented 47% of the early cohort, 25% were non-Hispanic, Black, 32% were non-Hispanic White, and 37% were Hispanic; however, in the Tennessee site, which represented 44% of the later cohort, 11% were non-Hispanic, Black, 73% were non-Hispanic White, and 14% were Hispanic. Despite differences in enrollment by site during the two time periods, we consistently found that most patients met one or more COVID-19 vaccine priority criteria and most had medical conditions associated with higher risk of severe outcomes. Second, although not a criterion in the early cohort, 100% of the later cohort included patients who had >1 sign or symptom of a COVID-like illness because of expanded testing to all A c c e p t e d M a n u s c r i p t 12 hospitalized patients; 90% of patients in the early cohort had >1 sign or symptom of a COVID-like illness. Similar results were found in a sensitivity analysis for ICU admission and severe outcomes excluding those without COVID-like signs or symptoms. We included outcome measures that were clinically meaningful and reflected disease severity, including non-invasive and invasive mechanical ventilation. Use of non-invasive mechanical ventilation increased substantially from the first to the second time period, which might reflect concerns about risk of lung injury from invasive ventilation in adults with COVID-19, availability of ventilators, or additional factors.

Conclusions
We   Any severe outcome was defined as: non-invasive ventilation, invasive mechanical ventilation, vasopressor support, dialysis/renal replacement therapy, extracorporeal membrane oxygenation, stroke, venous thromboembolic event, or death.