SARS-CoV-2 seroprevalence among children in Greece during Omicron variant period.

The Omicron variant is associated with increased transmissibility, but evidence about the impact of Omicron in seropositivity of children is limited. This study aims to evaluate SARS-CoV-2 seroprevalence in children during the different variants' subperiods. A prospective multicenter seroprevalence study was conducted in 7 University public hospitals in Greece from November 2021 to August 2022 (3 subperiods: November 2021-February 2022, March 2022-May 2022, June 2022-August 2022). Children from different age groups, admitted to the hospital or examined in outpatient clinics for reasons other than COVID-19 were enrolled. Neutralizing antibodies (Nabs), anti-Spike (anti-S) and anti-nucleocapsid (anti-N) SARS-CoV-2 IgG in serum were evaluated. A total of 2127 children (males:57,2%; median age:4,8years) were enrolled. Anti-N IgG seropositivity increased from 17,8% in the first sub-period to 40,7% in the second sub-period and then decreased in the third sub-period (36,7%). Anti-S IgG seropositivity appeared to have an increasing trend over the study period, starting from 34,8% and reaching 80,7%. Children aged 1-4 years old have significantly higher anti-N IgG titers compared to children aged 0-1 years old (p < 0,001). Infants have significantly lower anti-S IgG titers compared to all other age groups (p < 0,001). Immunocompromised children and infants have the lowest seropositivity for NAbs.Conclusions During the Omicron period, seropositivity significantly increased, as a result of higher transmissibility. Neonates and infants have lower antibody titers compared to other age groups, while young children aged 1-4 years old present higher antibody titers, suggesting that this age group may mount a higher antibody response. Continuous surveillance seroprevalence studies are needed in children, in order to identify the true extent of SARS-CoV-2 and guide the planning of adequate public health measures.

WHAT IS KNOWN: • Seroprevalence surveys among children may be extremely useful, in order to properly monitor the immunity, either natural or acquired, through the quantification of IgG antibodies and to plan further immunization policies. • There are variations in the seroprevalence of COVID-19 between the different periods, according to the vaccination rates, the type of circulating variant and the transmissibility of the virus. • The Omicron variant is associated with increased transmissibility, but evidence about the impact of Omicron in seropositivity of children is limited. WHAT IS NEW: • In this large multicenter seroepidemiological study, SARS-CoV-2 seroprevalence rate in children is higher during the Omicron period in comparison to the previous pandemic waves, due to the high transmissibility of the virus and the increased rates of reinfection. • Neonates and infants have lower antibody titers compared to other age groups, while young children aged 1­4 years old present higher antibody titers, indicating that the children of this age group mount a higher antibody response. • This study provides essential information about immunity and the level of protection in the pediatric population, as neutralizing antibodies were evaluated, in addition to the anti-N and anti-S IgG antibodies.

SARS-CoV-2 Antibody Kinetics in Unvaccinated Hospitalized Children With COVID-19.

BACKGROUND: Antibody levels decline a few months post-acute COVID-19, but humoral memory persists in adults. Age and disease severity may affect antibody responses. This study aims to evaluate the presence and durability of antibody responses in children with COVID-19. METHODS: A prospective, single-center study, involving unvaccinated children 0-16 years of age who were hospitalized with COVID-19 between October 2020 and December 2021, was conducted. Serological testing for anti-Spike severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) IgG and neutralizing antibodies was performed at diagnosis and at 1-, 3-, 6- and 12-months post-infection. RESULTS: A total of 65 immunocompetent children were enrolled [mean age (±SD): 6.7 (±6.4) years; males: 56.9%]. At 3 months, 40/44 (91%) children were seropositive; seropositivity persisted in 22/26 (85%) children at 6 months and in 10/12 (83%) children at 12 months. There was no evidence that age was modifying the prediction of variance of SARS-CoV-2 IgG levels. In contrast, SARS-CoV-2 IgG levels varied with time and disease severity. The association with time was non-linear, so that with increasing time there was a significant reduction in SARS-CoV-2 IgG levels [coef, 0.044 (95% confidence interval {CI}: 0.061-0.028), P < 0.001]. For each increment of time, the higher disease severity group was associated with 0.9 lower SARS-CoV-2 IgG levels. Everyone varied from the average effect of time with an SD of 0.01, suggesting that individuals may have different trajectories across time. CONCLUSION: Disease severity, but not age, influences antibody titers among children hospitalized with COVID-19. SARS-CoV-2 infection induces durable seroconversion in these children with detectable IgG levels at 1 year after infection.

Epidemiology of respiratory viruses among children during the SARS-CoV-2 pandemic: A systematic review and meta-analysis.

OBJECTIVE: This meta-analysis aimed to assess the prevalence of respiratory viruses among children under the special conditions of the COVID-19 pandemic. METHODS: Five databases were systematically searched to assess the pooled prevalence of various respiratory viruses in different age groups, regions, seasons, and in patients with and without confirmed SARS-CoV-2 coinfection. Moreover, we looked at the virus distribution in the first and second half of the pandemic and countries with distinct economic status. Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines were followed, and the systematic review was registered on PROSPERO (CRD42022379297). RESULTS: Enterovirus/rhinovirus and human respiratory syncytial virus (HRSV) were the most prevalent pathogens among children. The prevalence of HRSV increased in the second half of the pandemic. The prevailing viruses vary according to the SARS-CoV-2-coinfection status, season, region, and country´s economic status. CONCLUSION: This meta-analysis shows the epidemiology of respiratory viruses other than SARS-CoV-2 in children aged 0 to 12 years during the COVID-19 pandemic. Because major events, such as a pandemic, can alter epidemiology patterns, it is important to know them to improve health education measures, develop vaccines and medicines for vulnerable groups, as a guide for prevention strategies, and help with clinical decisions.

A Narrative Review on the Role of Dalbavancin in the Treatment of Bone and Joint Infections.

Bone and joint infections (BJI) require prolonged antimicrobial treatment, leading to lengthy hospitalizations, high costs, the risk of nosocomial infections, and the development of antimicrobial resistance. Dalbavancin is a novel semisynthetic lipoglycopeptide approved for the treatment of adults and children with acute bacterial skin and skin structure infections. This narrative review aims to summarize the characteristics of dalbavancin and the current scientific evidence regarding its clinical efficacy and safety in the treatment of BJI. A literature search until June 2023 was performed to identify all published research about the role of dalbavancin in the management of BJI. Due to its unique pharmacokinetics characterized by prolonged half-life, high bactericidal activity against most Gram-positive bacteria, a good safety profile, and high tissue penetration, dalbavancin can be a valuable alternative to the treatment of BJI. Clinical studies have shown its non-inferiority compared to conventional therapies in BJI, offering potent activity against key pathogens and an extended dosing interval that may shorten hospitalization. In conclusion, dalbavancin represents a promising treatment option for BJI with a favorable safety profile, but further research in both adults and particularly children, who are ideal candidates for long-acting antibiotics, is necessary to evaluate the role of dalbavancin in BJI.

New Insights into the Fluid Management in Patients with Septic Shock.

The importance of fluid resuscitation therapy during the early stages of sepsis management is a well-established principle. Current Surviving Sepsis Campaign (SSC) guidelines recommend the early administration of intravenous crystalloid fluids for sepsis-related hypotension or hyperlactatemia due to tissue hypoperfusion, within the first 3 h of resuscitation and suggest using balanced solutions (BSs) instead of normal saline (NS) for the management of patients with sepsis or septic shock. Studies comparing BS versus NS administration in septic patients have demonstrated that BSs are associated with better outcomes including decreased mortality. After initial resuscitation, fluid administration has to be judicious in order to avoid fluid overload, which has been associated with increased mortality, prolonged mechanical ventilation, and worsening of acute kidney injury. The "one size fits all" approach may be "convenient" but it should be avoided. Personalized fluid management, based on patient-specific hemodynamic indices, provides the foundations for better patient outcomes in the future. Although there is a consensus on the need for adequate fluid therapy in sepsis, the type, the amount of administered fluids, and the ideal fluid resuscitation strategy remain elusive. Well-designed large randomized controlled trials are certainly needed to compare fluid choices specifically in the septic patient, as there is currently limited evidence of low quality. This review aims to summarize the physiologic principles and current scientific evidence regarding fluid management in patients with sepsis, as well as to provide a comprehensive overview of the latest data on the optimal fluid administration strategy in sepsis.

Update of European Society of Clinical Microbiology and Infectious Diseases coronavirus disease 2019 guidelines: diagnostic testing for severe acute respiratory syndrome coronavirus 2.

SCOPE: Since the onset of COVID-19, several assays have been deployed for the diagnosis of SARS-CoV-2. The European Society of Clinical Microbiology and Infectious Diseases (ESCMID) published the first set of guidelines on SARS-CoV-2 in vitro diagnosis in February 2022. Because the COVID-19 landscape is rapidly evolving, the relevant ESCMID guidelines panel releases an update of the previously published recommendations on diagnostic testing for SARS-CoV-2. This update aims to delineate the best diagnostic approach for SARS-CoV-2 in different populations based on current evidence. METHODS: An ESCMID COVID-19 guidelines task force was established by the ESCMID Executive Committee. A small group was established, half appointed by the chair, and the remaining selected with an open call. The panel met virtually once a week. For all decisions, a simple majority vote was used. A list of clinical questions using the population, intervention, comparison, and outcome (PICO) format was developed at the beginning of the process. For each PICO, 2 panel members performed a literature search focusing on systematic reviews with a third panellist involved in case of inconsistent results. The panel reassessed the PICOs previously defined as priority in the first set of guidelines and decided to address 49 PICO questions, because 6 of them were discarded as outdated/non-clinically relevant. The 'Grading of Recommendations Assessment, Development and Evaluation (GRADE)-adoption, adaptation, and de novo development of recommendations (ADOLOPMENT)' evidence-to-decision framework was used to produce the guidelines. QUESTIONS ADDRESSED BY THE GUIDELINES AND RECOMMENDATIONS: After literature search, we updated 16 PICO questions; these PICOs address the use of antigen-based assays among symptomatic and asymptomatic patients with different ages, COVID-19 severity status or risk for severe COVID-19, time since the onset of symptoms/contact with an infectious case, and finally, types of biomaterials used.

Ileal bypass for pruritus relief in a 3-year-old boy with advanced progressive familial intrahepatic cholestasis: how effective is it?

Progressive familial intrahepatic cholestasis (PFIC) is a group of liver disorders that manifest in early childhood with cholestasis and pruritus resulting progressively in liver failure. We present a case of a 3-year-old boy with advanced PFIC from refractory pruritus. In order to offer an effective treatment of pruritus, our patient underwent ileal bypass and after a 2-month period free of symptoms, unexpectedly relapsed after a Rota viral infection. Finally, the child underwent orthotopic liver transplantation. Patients with advanced PFIC do not seem to benefit from nontransplant invasive interventions regarding the relief of pruritus.

Cardiovascular disease and risk assessment in people living with HIV: Current practices and novel perspectives.

Human immunodeficiency virus (HIV) infection represents a major cardiovascular risk factor, and the cumulative cardiovascular disease (CVD) burden among aging people living with HIV (PLWH) constitutes a leading cause of morbidity and mortality. To date, CVD risk assessment in PLWH remains challenging. Therefore, it is necessary to evaluate and stratify the cardiovascular risk in PLWH with appropriate screening and risk assessment tools and protocols to correctly identify which patients are at a higher risk for CVD and will benefit most from prevention measures and timely management. This review aims to accumulate the current evidence on the association between HIV infection and CVD, as well as the risk factors contributing to CVD in PLWH. Furthermore, considering the need for cardiovascular risk assessment in daily clinical practice, the purpose of this review is also to report the current practices and novel perspectives in cardiovascular risk assessment of PLWH and provide further insights into the development and implementation of appropriate CVD risk stratification and treatment strategies, particularly in countries with high HIV burden and limited resources.

Immunogenicity 6 months post COVID-19 mRNA vaccination among adolescents with juvenile idiopathic arthritis on treatment with TNF inhibitors.

OBJECTIVES: Mass vaccination is the most effective strategy for controlling the COVID-19 pandemic. This study aimed to evaluate the 6-month immunogenicity after BNT162b2-COVID-19 vaccination in adolescents with JIA on TNFi treatment. METHODS: This single-centre study included adolescents with JIA treated with TNFi for at least 18 months. Patients received two doses of COVID-19 vaccine (Pfizer-BioNTech) from 15 April to 15 May 2021. Quantitative measurement of IgG antibodies to SARS-CoV-2-spike-protein-1 was performed at 1, 3 and 6 months post-vaccination. RESULTS: Overall, 21 adolescents with JIA in clinical remission at the time of vaccinations were enrolled. None of them discontinued TNFi/MTX treatment at the time of vaccine administration or during the follow-up period. All patients developed a sustained humoral response against SARS-CoV-2 at 1 and 3 months after vaccination (P < 0.05). The antibody levels decreased significantly at 6 months post-vaccination (P < 0.01). The type of JIA did not reveal any differences in the humoral response at 3 (P = 0.894) or 6 months post-vaccination (P = 0.72). No difference was detected upon comparison of the immunogenicity between the different treatment arms (adalimumab vs etanercept) at 3 (P = 0.387) and 6 months (P = 0.526), or TNFi monotherapy vs combined therapy (TNFi plus methotrexate) at 3 (P = 0.623) and 6 months (P = 0.885). CONCLUSIONS: Although mRNA vaccines develop satisfactory immunogenicity at 1 month and 3 months post-vaccination in adolescents with JIA on TNFi, SARS-CoV-2 antibody titres decrease significantly overtime, remaining at lower levels at 6 months. Further collaborative studies are required to determine long-term immunogenicity, real duration of immune protection and the need for a booster vaccine dose.

Performance of point-of care molecular and antigen-based tests for SARS-CoV-2: a living systematic review and meta-analysis.

BACKGROUND: Molecular and antigen point-of-care tests (POCTs) have augmented our ability to rapidly identify and manage SARS-CoV-2 infection. However, their clinical performance varies among individual studies. OBJECTIVES: The evaluation of the performance of molecular and antigen-based POCTs in confirmed, suspected, or probable COVID-19 cases compared with that of laboratory-based RT-PCR in real-life settings. DATA SOURCES: MEDLINE/PubMed, Scopus, Embase, Web of Science, Cochrane Library, Cochrane COVID-19 study register, and COVID-19 Living Evidence Database from the University of Bern. STUDY ELIGIBILITY CRITERIA: Peer-reviewed or preprint observational studies or randomized controlled trials that evaluated any type of commercially available antigen and/or molecular POCTs for SARS-CoV-2, including multiplex PCR panels, approved by the United States Food and Drug Administration, with Emergency Use Authorization, and/or marked with Conformitè Europëenne from European Commission/European Union. PARTICIPANTS: Close contacts and/or patients with symptomatic and/or asymptomatic confirmed, suspected, or probable COVID-19 infection of any age. TEST/S: Molecular and/or antigen-based SARS-CoV-2 POCTs. REFERENCE STANDARD: Laboratory-based SARS-CoV-2 RT-PCR. ASSESSMENT OF RISK OF BIAS: Eligible studies were subjected to quality-control and risk-of-bias assessment using the Quality Assessment of Diagnostic Accuracy Studies 2 tool. METHODS OF DATA SYNTHESIS: Summary sensitivities and specificities with their 95% CIs were estimated using a bivariate model. Subgroup analysis was performed when at least three studies informed the outcome. RESULTS: A total of 123 eligible publications (97 and 26 studies assessing antigen-based and molecular POCTs, respectively) were retrieved from 4674 initial records. The pooled sensitivity and specificity for 13 molecular-based POCTs were 92.8% (95% CI, 88.9-95.4%) and 97.6% (95% CI, 96.6-98.3%), respectively. The sensitivity of antigen-based POCTs pooled from 138 individual evaluations was considerably lower than that of molecular POCTs; the pooled sensitivity and specificity rates were 70.6% (95% CI, 67.2-73.8%) and 98.9% (95% CI, 98.5-99.2%), respectively. DISCUSSION: Further studies are needed to evaluate the performance of molecular and antigen-based POCTs in underrepresented patient subgroups and different respiratory samples.

Seroprevalence of anti-SARS-CoV-2 antibodies among children and their parents in Greece.

School closures were enforced as measures to restrain the COVID-19 pandemic, based on the assumption that young children may play a key role in SARS-CoV-2 spread. This study aims to determine the prevalence of SARS-CoV-2 IgG antibodies in children and corresponding parents, in order to improve surveillance and estimate the prevalence of asymptomatic or subclinical COVID-19 cases. A prospective multicenter study was conducted between March and June 2021 in Greece. Children admitted to the hospital or examined in outpatient clinics for reasons other than COVID-19 and their parents were tested for anti-Spike SARS-CoV-2 IgG in serum. A questionnaire about clinical and demographic data was completed. The study included 823 participants: 427 children and 396 corresponding parents. The overall seroprevalence was 16.4% in parents and 13.8% in children. Among families with ≥ 1 seropositive child or parent, the combination of a seropositive parent and a corresponding seronegative child was 29.6%, a seronegative parent and a corresponding seropositive child was 24.7%, and a seropositive child with a corresponding seropositive parent was 45.7%. Age, level of education, and school or work attendance were not significantly associated with increased seropositivity. On the contrary, ethnic minority of Roma, close contact with known COVID-19 case, previous symptoms consistent with COVID-19, and mass gatherings were risk factors for seropositivity. CONCLUSION: The spread of SARS-CoV-2 during a period of lockdown in Greece was low in children and comparable to adults most likely due to intrafamilial transmission. Accordingly, it is unlikely that children have boosted virus transmission. WHAT IS KNOWN: • In the earliest months of the pandemic, it was demonstrated that children had significantly lower seroprevalence rates than the older age groups, due to the fact that children had decreased exposure to the virus, because of early public health interventions, such as school and day care closure. • Later, further studies reported that children have similar incidence rate of SARS-CoV-2 infection compared to adults in households and community settings. WHAT IS NEW: • In this seroprevalence study, the spread of SARS-CoV-2 infection during a period of lockdown in Greece with the predominance of the Alpha-variant was particularly low in children and comparable to adults, most likely due to intrafamilial transmission. • These study findings will be useful for decisions regarding non-pharmaceutical interventions during the pandemic, and especially, to guide in designing and implementing appropriate containment measures for schools and social gatherings.

The Psychological Impact of COVID-19 Admission on Families: Results from a Nationwide Sample in Greece.

The aim of the present study was to assess the psychological impact of hospitalization during the COVID-19 pandemic on parents and their offspring. We performed a nationwide cross-sectional study in Greece based on an Internet questionnaire survey. A convenience sample of parents whose offspring had been hospitalized due to COVID-19 (including multisystem inflammatory syndrome in children, MIS-C), diagnosed with COVID-19 but not hospitalized, and hospitalized for another reason during the pandemic were enrolled. Parental stress was assessed using the Perceived Stress Scale (PSS) and the Revised Impact of Event Scale (IES-R) tools, and childhood mental wellbeing with the Children's Revised Impact of Event 13 (CRIES-13) scale. Out of 214 received responses, stress levels were significantly higher in parents whose children had been admitted for COVID-19 or MIS-C versus those not admitted or admitted for other reasons (p < 0.001, for PSS/IES-R). Parental and childhood stress levels were correlated. In the multivariable linear regression analysis, children's hospitalization because of COVID-19 or MIS-C, younger parental age, the existence of comorbidities, and another family member's hospitalization because of COVID-19 were independent factors for higher stress. In light of the above, stricter hospital admission criteria for COVID-19 could be implemented, and psychological support for eventually admitted families may be beneficial.

Clinical Characteristics of Patients with Erythema Nodosum and Risk of Relapse - a 17-Year Study.

Erythema nodosum (EN) is the most common type of septal panniculitis which causes inflammation of the subcutaneous fat, being the result of a hypersensitivity reaction to specific triggers. It usually presents with erythematous painful rounded lumps symmetrically on the anterior surface of the lower limbs. Rarely, it may occur in other areas such as thighs, neck and arms. This is a retrospective study describing a cohort of patients hospitalized in the University Hospital of Heraklion, Heraklion, Greece. The present research compares characteristics between patients with and without relapse and identifies independent factors associated with relapse. All patients with EN hospitalized during a 17-year period were included. Data regarding epidemiology, current or recent infections, symptoms, laboratory values and relapses were all recorded and evaluated. In total, 138 patients, of which 27 (19.6%) males, with a median age of 46.5 years, were evaluated. Clinical presentation involved multiple lesions in 115 (83.3%) patients, while 12 (8.7%) of them were febrile. Relapse was noted in 27 (19.6%) subjects. Multivariate logistic regression analysis showed that male gender was associated with a higher risk of relapse, while cases with multiple lesions were associated with a lower risk.

Time between onset of symptoms and definitive treatment in children with acute appendicitis: How it affects length of hospital stay?

Purpose: Any delay in treatment of acute appendicitis (AA) could lead to complications increasing morbidity and length of hospital stay (LHS). The aim of this study was to determine the time interval between onset of symptoms and seeking medical attention and definitive treatment in children with AA and its impact on LHS. Materials and Methods: A prospective study was conducted from December 2017 to March 2018. All patients diagnosed with AA and who underwent surgical procedure were enrolled. A questionnaire leaflet completed by parents was used to collect clinical data and information about seeking medical attention and children's management. Time was divided into six different intervals (1-2 h, 3-6 h, 7-12 h, 13-24 h, >24 h and >48 h) to estimate the time between onset of symptoms and seeking medical attention and time between hospital admission and surgical procedure. LHS was recorded. Results: During the study period, 125 children were enrolled. Over half of the patients sought for medical assistance relatively soon (3-12 h) after the onset of symptoms, whereas 17.6% sought late healthcare (>24 h). The time between the medical examination and surgical procedure was <24 h in approximately 80% of the children. LHS was affected by time between onset of symptoms and seeking medical attention and time between medical examination and surgical procedure (P = 0.001 and P = 0.017, respectively). Conclusions: The majority of the children with AA admitted to hospital were treated relatively soon after the onset of symptoms. However, a significant proportion of children delayed to seek medical advice and undergo appendectomy, increasing LHS.

Recognizing and Managing Pancreaticopleural Fistulas in Children.

Background: Pancreaticopleural fistula, an abnormal communication between the pancreas and the pleural cavity, is a rare complication of pancreatic disease in children and is mainly associated with acute pancreatitis, chronic pancreatitis, trauma or iatrogenicinjury. The present review presents the current available data concerning the pathogenesis, clinical features, diagnosis and management of this unusual but difficult clinical problem among children, in order to shed light on its pathologic manifestation and raise clinical suspicion.Methods: The review of the literature was performed through a PubMed search of pediatric original articles and case reports, using the key words "pancreaticopleural fistula", "pancreatitis", "pleural effusion", "pseudocyst" and "children". The literature search revealed 47 cases of pediatric patients with pancreaticopleural fistula.Results: Diagnosis is based on the patient's medical history, physical examination and imaging, while the cornerstone of diagnosis is the presence of high pleural effusion amylase levels. The management of this disorder includes conservative, endoscopic and surgical treatment options. If treated promptly and properly, this clinical entity could have a lower rate of complications.Conclusions: The incidence of pancreaticopleural fistula in children may be underestimated in the literature, due to a reduced degree of clinical suspicion. A more heightened awareness of this entity is needed to improve the quality of life in children that suffer from this condition, as early diagnosis is essential for effective treatment and improved outcome.

Favorable Outcome in Infants Hospitalized With COVID-19: Single Center Experience from Athens, Greece.

This study aims to describe the clinical characteristics and outcome of 92 infants (aged <12 months) with community-acquired coronavirus disease 2019 (COVID-19) between March, 2020 and June, 2021 at a single center in Athens. Infants with COVID-19 developed mild disease (89, 96.7%), and were infected mostly by their household contacts (74, 80.4%). Disease complications were rare, indicating that hospitalization is the result of low threshold for admission rather than disease severity.

Effects of low molecular weight heparin and fondaparinux on mortality, hemorrhagic and thrombotic complications in COVID-19 patients.

Background: Coronavirus disease 2019 (COVID-19) is associated with increased thrombosis prevalence. However, there are insufficient data supporting the appropriate anticoagulation dose in COVID-19. Objective: We aim to systematically assess the currently available data regarding the effects of different dosing regimens of low molecular weight heparin and/or fondaparinux (LMWH/F) on mortality risk as well as the risk of arterial/venous thrombotic events and hemorrhagic complications in confirmed COVID-19 cases. Design: We conducted a living systematic review and meta-analysis on the effects of different LMWH/F doses on mortality, thrombotic and hemorrhagic events in COVID-19 patients. Data Sources and Methods: MEDLINE, Scopus, Embase, Cochrane Library, Cochrane COVID-19 study register, European Union Drug Regulating Authorities Clinical Trials Database, and ClinicalTrials.gov were searched to detect observational cohort studies and randomized-controlled clinical trials (RCTs) comparing difference doses of LMWH/F among confirmed COVID-19 cases. Results: Thirty-one eligible studies (6 RCTs and 25 cohort studies) with 11,430 hospitalized patients were included. No association was found between LMWH/F and mortality during the following comparisons: (1) no LMWH/F versus any LMWH/F; (2) prophylactic versus higher than prophylactic LMWH/F; (3) prophylactic versus therapeutic LMWH/F; (4) intermediate versus therapeutic LMWH/F; and (5) lower than therapeutic versus therapeutic LMWH/F. Mortality was higher in patients receiving prophylactic versus intermediate LMWH/F (OR = 2.01; 95% CI: 1.19-3.39). However, this effect was mostly driven by observational data. No associations were detected between the intensity of LMWH/F and the risk of thrombotic and hemorrhagic events, except the lower risk for hemorrhage in patients on prophylactic compared to higher LMWH/F doses. Conclusion: The risk for all-cause mortality was higher in patients receiving prophylactic LMWH/F compared to those on an intermediate dose of LMWH/F, based on observational data. These results should be interpreted in light of the moderate quality and heterogeneity of the included studies. Registration: The study protocol has been registered in the International Prospective Register of Ongoing Systematic Reviews PROSPERO (Registration number: CRD42021229771).