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Mortality rate and risk among hospitalized COVID-19 patients during different surges of the pandemic

In a recent study published in Scientific Reports, researchers assessed the mortality rates associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Alpha (B.1.1.7) and Delta (B.1.617.2) variant infections.

Study: Mortality among hospitalized COVID-19 patients during surges of SARS-CoV-2 alpha (B.1.1.7) and delta (B.1.617.2) variants. Image Credit: Hananeko_Studio/Shutterstock


SARS-CoV-2 has evolved into new variants worldwide since the coronavirus disease 2019 (COVID-19) pandemic began. Variants are defined by the World Health Organization (WHO) using three criteria: Greater transmissibility, increased virulence or a change in clinical symptoms, and a decline in the effectiveness of public health measures, vaccines, and treatment.

Due to the many stages of COVID-19 waves, time periods, variety of underlying comorbidities of patients, and hospital load, the trajectory of mortality due to COVID-19 is diverse and challenging to describe. The mortality trend also coincided with the trend of intensive care unit (ICU) mortality, which was caused by the large number of cases that needed admission to the ICU during the pandemic. Since the sudden surge of patients could have a negative impact on their outcomes, research is needed to assess the trajectory of mortality over time between COVID-19 waves.

About the study

In the present study, researchers assessed the mortality rate and mortality risk associated with COVID-19 hospitalized patients across various COVID-19 surges.

Between 21 March 2021 and 3 October 2021, hospitalized COVID-19 patients from Tehran province participated in this multicenter observational study. The registry database monitored by the Coronavirus Control Operations Headquarters in Tehran was used to obtain study data. In March 2020, the nation of Iran launched its central registry for novel coronavirus infections. Following WHO definition guidelines, all suspected, potential, and confirmed COVID-19 cases were prospectively documented on the national register of COVID-19 database.

The primary study outcome was mortality among COVID-19-positive hospitalized patients. Censored cases were defined as patients who were either discharged or unavailable for follow-up. The interval from the date of admission until the date of death or discharge was termed survival time. In addition to the demographic factors such as age, gender, smoking habits, and nationality, the study involved variables like symptoms including anorexia, vomiting, paralysis, diarrhea, fever, muscular pain, anosmia, and loss of taste; comorbidities including heart disease, hypertension, human immunodeficiency viruses (HIV), neurological illness, asthma, neurological disease, hypertension, and immunodeficiency; drug abuse, county of residence, and computed tomography (CT) results.


From 21 March 2021 to 3 October 2021, 270,624 patients COVID-19-positive patients were hospitalized in Tehran. Patients with COVID-19 had a median age of 50 years, including 50.2% males, and by mid-August, there were two peaks in the number of COVID-19-hospitalized patients. These peaks were associated with the prevalence of the SARS-CoV-2 Alpha and Delta variants, respectively. During the second peak, patients were more likely to belong to the youngest age group. Among the first and second peaks, there was no difference with respect to the proportion of patients admitted to the ICU and those who were not.

In March, the percentage of COVID-19-infected men was 51.9, which declined to 47.3 in October. The median age of patients decreased from 55 in March to 48 in October. The number of patients aged less than 40 years was 25.5, between 40 and 49 years was 16.5, and between 50 and 59 years was 19.1 during the first peak observed in April. Subsequently, the number of patients increased to 31.4, 20.0, and 21.0 in the second peak in August. Reversing the pattern for patients 60 years and older, a lower proportion of hospitalized patients was noted for this age group in August than in April.

During the research period, 18,623 COVID-19 patients succumbed. Patients with COVID-19 admitted to non-ICU wards had a death rate of 3.2, whereas those admitted to ICUs had a death rate of 34.0. The strongest correlations were found between patient outcome and age, the number of days hospitalized, respiratory distress, comorbidities, kidney illness, chest discomfort, hypertension, and diabetes.

Patients admitted in June displayed a decreased risk of COVID-19 death compared to those hospitalized in March. Men had a 17% greater risk of mortality than women. The chance of succumbing to COVID-19 elevated with age, with people over 89 years old having the highest risk. Furthermore, a  higher number of comorbidities was linked to a higher risk of COVID-19 death, and those suffering from three or more comorbidities were at greater risk.

Death rates among ICU-admitted patients rose between March and April before stabilizing until May and declining during the first COVID-19 peak in January. The death rate surged in July at the second peak, rose to its highest point in August, then decreased in September and October. However, mortality spiked in April and July among non-ICU patients. Additionally, non-ICU patients accounted for the highest percentage of mortality during the first COVID-19 peak.


Overall, the study findings showed that while the death proportion declined between March and October 2021, hospitalization and COVID-19 death risk increased. Furthermore, compared to the surge in SARS-CoV-2 Alpha variant infections, the Delta variant surge was linked to a greater probability of COVID-19 death.

Journal reference:
  • Zali, A. et al. (2022) "Mortality among hospitalized COVID-19 patients during surges of SARS-CoV-2 alpha (B.1.1.7) and delta (B.1.617.2) variants", Scientific Reports, 12(1). doi: 10.1038/s41598-022-23312-8.

Posted in: Medical Science News | Medical Research News | Disease/Infection News

Tags: Anorexia, Anosmia, Asthma, Computed Tomography, Coronavirus, Coronavirus Disease COVID-19, covid-19, CT, Diabetes, Diarrhea, Drug Abuse, Fever, Heart, Heart Disease, HIV, Hospital, Immunodeficiency, Intensive Care, Kidney, Mortality, Neurological Disease, Pain, Pandemic, Paralysis, Public Health, Research, Respiratory, SARS, SARS-CoV-2, Severe Acute Respiratory, Severe Acute Respiratory Syndrome, Smoking, Syndrome, Tomography, Vomiting

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Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.

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