Convalescent Plasma Therapy in Severe and Critically Ill COVID-19 Patients: A Systematic Review and Meta-Analysis


 Background: Convalescent plasma treatment of severe and critically ill Corona Virus Disease 2019(COVID-19) patients is still controversial.Objective: To evaluate the efficacy and safety of convalescent plasma in patients with severe COVID-19 infection and critically ill patients, We performed a meta-analysis and systematic review of convalescent plasma therapy in severe and critically ill COVID-19 patients.Methods: We conducted a literature search in electronic data and citations of previously published systematic reviews. We included only randomized controlled studies on convalescent plasma for the treatment of severe and critically ill COVID-19 patients. Results: A total of 7 randomized controlled trials and 1363 patients were included in the meta-analysis. Compared to patients of the control group, there was no difference in clinical improvement (Four studies, RR 1.06, 95% CI 0.96 to 1.17, p = 0.22, moderate certainty) and mortality (seven studies, RR 0.86, 95% CI 0.66 to 1.11, p = 0.48, moderate certainty) for patients of convalescent plasma therapy group.Conclusion: Convalescent plasma does not reduce the improvement of symptoms and the risk of death in severely infected and critically ill COVID-19 patients


Introduction
COVID-19 infection is a highly contagious and harmful disease. From December 2019 to February 2021, more than one hundred million patients and 2 million deaths are caused by COVID-19 in 210 countries [1] .
Epidemiology Working Group for NCIP Epidemic Response reported that 14% of patients would develop severe infections and suffer severe progressive pneumonia and multiple organ failure [2,3]. There is a lack of effective treatment for COVID-19.
Convalescent plasma was collected from recovered patients with infections [4]. Convalescent plasma was used to treat SARS, the Middle East respiratory syndrome (MERS) [5,6]. But Convalescent plasma treatment of severe COVID-19 infection is still controversial [2,7]. A systematic review has reported that convalescent plasma reduces the risk of death in patients with severe COVID-19 disease [8]. However, several RCT studies have reported different results in severely infected patients [9,10]. We performed a systematic review and meta-analysis to evaluate the e cacy and safety of convalescent plasma in patients with severe COVID-19 infection and critically ill patients.

Registration
The project was registered on PROSPERO(CRD42021274365). We performed a meta-analysis and systematic review of convalescent plasma transfusion therapy in severe and critical COVID-19 patients.

Information sources
We conducted a literature search of the following electronic data: PubMed, Cochrane Library, Web of Science, EMBASE. Meanwhile, citations of previously published systematic reviews were searched. The deadline for the search was August 18, 2021.

Literature inclusion criteria
We included only randomized controlled studies on convalescent plasma for the treatment of severe and critical COVID-19 patients. Prospective observational studies, retrospective studies, case reports, case series, and retrospective studies were excluded.

Study Selection and Data Extraction
Two independent reviewers performed a literature search and screening. First, reviewers screened the titles of the literature and then assessed the complete manuscripts. Duplicate references were eliminated. We will extract the following information: 30d symptom improvement rate, mortality, 3d, and 7d nucleic acid conversion rate, oxygen support time, hospitalization time, 30d discharge rate, and adverse events. Adverse events include severe allergy, severe respiratory and cardiac symptoms, hemolysis, etc. At the same time, patients' basic information was extracted: age, FiO 2 , SOFA score, plasma usage control method, control group treatment method, etc. If the median and interquartile-range (IQR) were reported for continuous variables in the data, we would convert the data to mean and standard deviation [11,12] .

Outcomes
The primary outcomes included: 30d symptom improvement rate and 30d mortality rate. Secondary outcomes included: 3-day and 7-day nucleic acid conversion rate, duration of oxygen support, duration of hospital stay, 30-day discharge rate.

Risk of bias assessment and quality evaluation
The reviewers assessed the risk of bias (RoB) independently using a modi ed Cochrane RoB tool. Random sequence generation, allocation concealment, blinding method, selective reporting bias, and other biases were evaluated. Risks were classi ed low, high, and unknown. For the research results, we also performed a GRADE evaluation [13].

Statistics
Two researchers carried out the data analysis. Mantel-Haenszel statistics and inverse variance models were used in the meta-analysis. Outcome data were analyzed by Review Manager 5.3 for research. The inverse variance model assessed study weights. As a result of dichotomous variables such as mortality, we will calculate the relative risk. We will calculate the mean, standard deviation (SD), and both with 95% con dence intervals (CI) for continuous variables. The x 2 test, I 2 , evaluated homogeneity. I 2 ≥ 50% is high heterogeneity.
When there was high heterogeneity, we would conduct a sensitivity analysis or use a random model. For the primary outcomes, we would conduct sequential research to evaluate whether the sample size of the results is su cient. In the trial sequential analysis (TSA), the required information size was based on a type I error of 5%, a beta of 20%, the proportion of participants in the control group with the outcome, and a relative risk reduction of 15% and 30%.

Subgroup analysis
Li et al. reported convalescent plasma therapy might be effective for severely infected patients, but it is ineffective for critically ill patients [2]. We performed the subgroup analysis for severe patients and critically ill patients studies in clinical improvement and mortality.

Results
A total of 832 articles were retrieved, of which 830 were retrieved in electronic data from PubMed, Embase, Web of SCI, and Cochrane Library, and 2 papers were retrieved in a previously published meta-analysis [14,15].476 records were retrieved after removal of duplicates. By reading the title and abstract, we excluded the unrelated literature on the convalescent plasma treatment of COVID-19. We read the full text and selected studies that met the inclusion criteria, excluded studies that met the exclusion criteria, and studies that data cannot be extracted. A total of 7 randomized controlled trials and 1363 patients were included in the metaanalysis [2,7,9,[14][15][16][17] (Fig. 1).

Primary outcomes
Compared to patients of the control group, there was no difference in clinical improvement (Four studies, RR 1.06, 95% CI 0.96 to 1.17, p = 0.22, moderate certainty) (Fig. 4) and mortality (seven studies, RR 0.86, 95% CI 0.66 to 1.11, p = 0.48, moderate certainty) (Fig. 5) for patients of convalescent plasma therapy group. We performed a sequential analysis of mortality. A total of 1,363 patients were included in our study, with an actual sample size of 3,330 required (Fig. 6). Outcome estimates were based on the following statistical indicators: the probability of type I error (α = 0.05), probability of type II error (b = 0.2), relative risk reduction (RRR = 30%), and 15% event rate in the control group. The TSA results showed that the cumulative Z value did not cross the traditional cut-off, nor did it cross the TSA cut-off, nor did it reach the required patient sample size. This indicates that further validation is still needed to verify a difference in safety between the two groups.

Secondary outcomes
Time of respiratory support The trial of Agarwal A and the trial of O'Donnell MR reported on the duration of respiratory support [7,16]. But data on the time of respiratory support could not be converted to mean and SD. Therefore, we were unable to conduct a meta-analysis of the timing of respiratory support. Compared to control group patients, time of respiratory support of convalescent plasma group patients was no different in the trial of Agarwal A (median 9 days, IQR: 6 to 13 vs. 10 days, IQR:6 to 13, p = 0.7) and the trial of O'Donnell MR (median 6 days, IQR: 3 to 16 vs. 7 days, IQR:3 to 11, p = 0.508). The trial of Sekine L reported on the duration of time without respiratory support, and there was no difference in the duration of time without respiratory support between patients in the convalescent plasma treatment group and control patients.

Time to hospital discharge
Six trials reported on time to hospital discharge [2,7,9,[15][16][17]. The data of time to hospital discharge could not be extracted in the trial of Li and Simonovich VA [2,17]. In the trial of O'Donnell MR, time to hospital discharge could not be converted to mean and SD. The meta-analysis showed no difference in time to hospital discharge (three studies, MD -1.21day, 95% CI -4.78 to 2.36, p = 0.51, very low certainty) (Fig. S1) between patients in the convalescent plasma treatment group and those in the control group.

Discharge rate
Four trials reported discharge rates at 28 or 30 days [2,7,9,17]. There was no difference in discharge rate (Four studies, RR 1.06, 95% CI 0.96 to 1.17, p = 0.43, moderate certainty) (Fig. S4) between patients in the convalescent plasma therapy group and those in the control group.

Discussion
Our study found that convalescent plasma treatment of patients with severe and critical covid-19 infection did not increase the rate of symptomatic improvement, nor did it reduce the risk of death. At the same time, convalescent plasma does not reduce the length of stay in the hospital or the length of time the patient is on oxygen. Convalescent plasma also had no signi cant effect on the 72h nucleic acid conversion rate and 30day discharge rate, with a tendency to increase the 7-day nucleic acid conversion rate, but there was no statistically signi cant difference. COVID-19 infection is a highly infectious disease with a high risk of death [18].COVID-19 virus can invade multiple organs, including the lungs, kidneys, liver, heart,brain, and other organs, causing acute respiratory distress syndrome, infectious shock, and multiple organ failure [19]. The lungs are a common target organ, and studies have reported a positive correlation between the severity of lung infections and respiratory viral load [20]. Convalescent plasma reduces viral infectivity by binding to the virus and removes pathogens through various pathways such as complement activation and phagocytosis [21]. Libster et al. reported that early administration of recovery plasma within 3 days in patients presenting with mild disease signi cantly reduced the risk of progression to severe infection [22]. A recent meta-analysis reported similar ndings, with early convalescent plasma reducing the risk of patient death [23].
The use of recovery plasma in severely infected and critically patients remain controversial. Initially, Duan et al. recruited 10 patients with severe COVID-19 infection. They treated them with convalescent plasma transfusions, which resulted in a signi cant improvement in clinical symptoms, a signi cant decrease in in ammatory parameters, and an increase in the rate of nucleic acid conversion [24] . Subsequently, the FDA issued guidance on the use of convalescent plasma in COVID-19 patients, which also concluded that convalescent plasma could be requested in emergency situations for critically ill patients [25]. Max R et al. included 223 patients, 150 randomized to receive convalescent plasma and 73 to receive normal control plasma. It was found that convalescent plasma did not improve clinical symptoms but reduced the risk of death in patients with severe infections [7]. A meta-analysis by Zhang and Sun et al. incorporating observational and retrospective studies came to a similar conclusion that convalescent plasma reduces the risk of death in patients with severe infections [26,27]. However, recent RCT studies have found that convalescent plasma did not improve the prognosis of patients with severe disease [9,[14][15][16][17].
In our study, we found that convalescent plasma did not improve clinical symptoms, reduce the risk of death, reduce the time on oxygen, or improve the discharge rate of patients with severe infections and critical illnesses. This may be related to late use and low antibody titers after use [15,16,23]. Our study found that convalescent plasma had the potential to increase the 7d nucleic acid conversion rate in patients, but its p = 0.05, which still needs to be further reported in a large sample size study. However, the sequential analysis found that the sample size still fell short of the required sample size, and further study reporting is still needed.

Limitations
This study has the following limitations: 1. Antibodies need to be highly speci c to function, and we did not consider the effect of the new coronavirus variant on the results of this study. 2. Blood antibody titers following antibody infusion may affect the results. However, studies of adequate antibody titers in severe infections are still too few to group them according to antibody titers, and further research is needed.

Conclusion
Convalescent plasma does not reduce the improvement of symptoms and the risk of death in severely infected and critically ill patients, nor does it reduce the time on oxygen, the length of hospital stay, or the rate of discharge. There was a trend towards increased 7-day nucleic acid conversion rates in recovery plasma, but this was not statistically signi cant. The safety and effectiveness of convalescent plasma therapy in severe and critically ill COVID-19 patients still need more research. Contribution PY and JW designed the study and wrote the manuscript; JY revised the manuscript for controversial intellectual content and decided to submit the report. RZ nished the results and wrote some discussions. RT and XL prepared the gures. XL and YL performed a literature search and screening. All authors read and approved the nal manuscript.

Funding
This work was supported by the Yangzhou social development project (YZ2018075), Yangzhou Medical Talent (ZDRC201845).

Availability of data and materials
All data generated or analyzed during this study are included in this published article.
Ethics approval and consent to participate An approval by an ethics committee was not applicable.

Consent for publication
All authors have agreed to the publication of this manuscript.

Competing interests
There were no con icts of interest in this review.
Publisher's Note Springer Nature remains neutral concerning jurisdictional claims in published maps and institutional a liations. There was a minimum anti-SARS-CoV-2 total IgG antibody titer of at least 1:400 in convalescent plasma / Figure 6 Results of sequential analysis of mortality. TSA, trial sequential analysis.

Supplementary Files
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