A multicenter, retrospective cohort study was conducted on adult patients that were diagnosed with severe or critical COVID-19. The study involved a retrospective assessment of the medical records of patients who were admitted to tertiary specialized hospitals (Al-Hakeem and Al-Amal hospitals). Based on the treatment protocol whether it included CP therapy or not, the patients were allocated into two groups; the standard therapy group, that consisted of patients who received the standard therapy which mainly included antiviral agents, antibiotics, steroids and anticoagulants, according to the Iraqi ministry of health (MOH) approved guidelines. ¹¹ The second group was the plasma therapy group that consisted of patients who received CP combined with the standard therapy.

The study included patients that were admitted to Al-Hakeem and Al-Amal hospitals from June 1, 2020 till August 31, 2020, in Al-Najaf Province, Iraq. Al-Hakeem hospital is the first center for the admission of COVID-19 patients in Najaf, and it contains 264 beds. Al-Amal hospital has 170 beds, including 50 intensive care unit (ICU) beds, and it has been assigned as a referral center for severe and critical cases of COVID-19.

The Scientific Research Committee at Al-Najaf Health Directorate approved this study which involved Al-Hakeem hospital and the main blood bank with the approval number (19421), and Al-Amal hospital with approval number (30418). This study was also granted approval by the ethics and scientific committee of faculty of pharmacy/the University of Kufa with approval number (2403). All participants gave written informed consent to participate in this study. The current study is registered at Clinical Trials.gov ( https://clinicaltrials.gov/ct2/show/NCT04764747) with the registration number (NCT04764747). ¹²

Eligible participants were 18 years of age or older, with COVID-19 infection confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) test, who were hospitalized with severe or critical case of COVID-19. We excluded patients who did not require oxygen therapy, patients that were discharged or died within 48 hours of admission, patients with a history of allergy to plasma transfusion, and those with incomplete data on their medical records.

The study participants with severe COVID-19 were defined as patients who had oxygen saturation of less than or equal to 93%, therefore, they needed oxygen therapy. Patients with critical cases of COVID-19 were defined as patients who needed mechanical ventilation and ICU observation. ^{2 , 13}

The medical records of patients diagnosed with COVID-19 were taken from the archive unit of the tertiary specialized public hospital and reviewed retrospectively. Data collection period was from September 2020 to February 2021. Data was collected by using a chart extraction sheet which is used to collect information from patients' medical records. These medical records were selected based on chronological categorization in the statistical unit according to admission date. Blind data abstraction was performed for this study. Also, two senior physicians reviewed the data extracted from the medical records and approved the abstraction process. The chart extraction sheet consists of patients' demographics (age, gender, occupation, address), comorbidities (hypertension, coronary artery disease, type 2 diabetes mellitus (T2DM), obstructive airway disease, and chronic kidney disease), date of admission, date of discharge, length of stay in the hospital, symptoms (fever, cough, shortness of breath, fatigue, headache, sore throat, nausea and vomiting, oxygen-support categories were defined either as ambient air, low-flow oxygen, high-flow oxygen, and mechanical ventilation, ¹⁴ vital signs on admission (temperature, heart rate, oxygen saturation (SpO ₂%)). Additionally, laboratory parameters such as white cell counts, lymphocytes count, serum creatinine, D-dimer, ferritin, aspartate aminotransferase (AST), and alanine aminotransferase (ALT), were included. Lastly, type of medications, and outcomes, which was defined as in hospital mortality and clinical improvement (according to the modified World Health Organization (WHO) ordinary scale.), ^{13 , 14} were considered in the chart sheet. Information of plasma donor that was obtained from the plasma unit of the main blood bank consisting of donors' demographics, ID code of plasma bottle, and immunoglobulin G (IgG) titer ( See Underlying data: http://doi.org/10.5281/zenodo.4982052 ¹⁵ ) was also included.

In this study the primary outcome was the in-hospital mortality rate (MR) (number of deaths with a 21-day time frame). The secondary outcome was the association with various predictors (sociodemographic, clinical, laboratory variables and medications). Both these outcomes were examined with uni- and multivariate analysis.

The time to clinical improvement was also assessed. Clinical improvement for COVID-19 was defined as a reduction of two-points in a modified six-point scale, discharged or achieved criteria of discharge, which was defined as clinical recovery (i.e., SpO ₂ equal to 94% on room air, fever subsided, and relief of cough, all continued for at least 72 hours) (one-point); hospitalized without oxygen therapy (two-points); hospitalized on low-flow oxygen therapy (three-points); hospitalized on high-flow oxygen therapy (four-points); hospitalized and required mechanical ventilation (five-points); death (six-points). ^{14 , 16}

The sample size was based on all medical records available in the archive unit for patients admitted to these public hospitals during June, July, and August 2020. Total of 312 patients included in the statistical analysis as illustrated in ( Figure 1). Post hoc power analysis of sample size based on mortality outcome and level of significance at alpha = 0.05 (type I error) yielded statistic power of 97.3% (1- type II error) in detecting the deference between the two group of the study.

Normality test was performed for all variables. Normally distributed mean was used to present the data, while for variables with non-normal distribution median and interquartile range (IQR) (25% to 75% percentile range) were used. Chi-square test or Fisher exact test was used to analyze the discrete variable. To assess the difference in continuous variables; two-samples t-test (in normally distributed variables), and Mann-Whitney U test was used in variables with non-normal distribution. Kaplan–Meier analysis ¹⁷ was used to estimate the median time of the cumulative percentage of survival or clinical improvement, the Log-rank test was used to calculate the p-value and to compare the significance between the two groups. Lack of clinical improvement at day 21 and death before day 21 was considered as right censored for that day.

Univariate analysis was performed using Cox regression for all patients’ variables, and if p-value < 0.1, the variables were included in the multivariate Cox proportional hazard model to allow adjustment of certain confounder variables. The hazard ratio (HR) was calculated by using the Cox proportional hazard regression analysis, to find the time-dependent association of the model, in order to calculate the 95% confidence interval. Missing data were excluded from the final analysis.

SPSS 22.0.0 (Chicago, IL), GraphPad Prism version 8.1.0 for Windows ( https://www.graphpad.com/) was used for the statistical analysis. P-value was considered statically significant if less than 0.05.

In this cohort the mean age of the patients was 55.1(±13.6) years, and 70.2% were male. Overall, 82% of the hospitalized patients had cough and 81.4% had shortness of breath (SOB). The mean SpO ₂ was 82.7 % (which is consistent with the disease severity stage of the patients included in the study). All baseline characteristics of patients’ demography, comorbidities and clinical parameters of the two groups were not statistically significant, except for azithromycin and lopinavir/ritonavir that were significantly higher in patients treated with plasma therapy, while acetaminophen and favipiravir were significantly higher in patients treated with the standard therapy ( Table 1). Plasma characteristics are illustrated in Table.

The survival rate was 90.2% in the plasma therapy group compared to 84.2% in the standard therapy group, after 7 days. Additionally, the survival rate in the plasma therapy group was significantly higher (77.7%) compared to the standard group (60.5%) after 14 days (p-value = 0.010). This trend continued after 21 days in the plasma group (68.3%) vs. (46.8%) in the standard group, with a mean survival time of 17.6 in the plasma group and 15.3 in the standard therapy group ( Table 3 ).

Kaplan-Meier survival analysis revealed statistically significant improvement in the survival in the plasma therapy group, compared with the standard therapy group ( Figure 2 ).

The univariate analysis showed that the use of plasma compared to standard therapy resulted in a reduced risk of death by 54.7%. The results from the overall study population included in the multivariate model showed that plasma therapy has a statistically significant effect on improving the survival rate and it can be considered as an independent predictor of mortality. This adjusted analysis revealed a further reduction in the HR of the plasma therapy group from 0.557 (0.352-0.883) in unadjusted analysis to 0.368 (0.177-0.765). This meant that the reduction in the risk of death reached 63.2%, thus indicating that plasma therapy is more effective in improving survival rates. The increase in white blood cells (WBC), D-Dimer, and T2DM were independent predictors of mortality rate, while both the use of plasma and rivaroxaban reduced the risk of MR independently, as shown in Table 4.

In the multivariate analysis for the plasma therapy group, the result showed that as independent predictors of mortality, T2DM and D-Dimer are associated with increased mortality, while high antibody titer is associate with decrease mortality as illustrated in Table 5.

Interestingly, the median time to improvement was three days faster in plasma therapy than standard therapy (8 days vs. 11 days). Kaplan-Meier analysis showed a significant statistical difference between the two groups. The cumulative incidence of clinical improvement was significantly higher in patients who received plasma therapy (44.1%) then those who received standard treatment (18.1%), after 7 days. Treatment after 14 days indicated that the cumulative incidence of clinical improvement was higher in the plasma therapy (67.1%) vs. standard therapy group (58.8.9%). Additionally, 21 days post-treatment the cumulative incidence of clinical improvement was still significantly higher in plasma therapy (74.3%) compared to standard therapy group (65.0%) ( Table 6 and Figure 3)

Zenodo: Evaluating the effectiveness of convalescent plasma therapy and the factors that influence the therapeutic outcome in hospitalized COVID-19 patients: A retrospective cohort study.

http://doi.org/10.5281/zenodo.4982052. ³¹

The project contains the following underlying data:

Database: Data for CP in COVID-19 patients.

Data are available under the terms of the Creative Commons Zero “No rights reserved” data waiver ( CC0 1.0 Public domain dedication).