COVID-19 Resources

MDPI Comment on the COVID-19 Virus

Since 1996, MDPI has been committed to supporting the research community by providing the latest research freely available and making relevant and useful research available as quickly as possible. The world is current experiencing a pandemic of COVID-19, and researchers are working extremely hard to understand it and find a cure.

The values MDPI holds strongly are particularly important at the moment, and we will continue to publish relevant, peer-reviewed research as quickly as possible in open access format. This means that it will immediately be available for researchers, health professionals, and the general public to read, distribute, and reuse. We believe that scientific advancements will be crucial to overcoming this pandemic, and will do everything we can to support researchers working looking for solutions.

This page contains a variety of information related to COVID-19 available from MDPI, including journal articles, special issues, and preprints, among others.

25 pages, 3253 KiB

Open AccessReview

Multisystem Endothelial Inflammation: A Key Driver of Adverse Events Following mRNA-Containing COVID-19 Vaccines

by János Szebeni and Akos Koller

Vaccines 2025, 13(8), 855; https://doi.org/10.3390/vaccines13080855 (registering DOI) - 12 Aug 2025

Abstract

mRNA-LNP-based COVID-19 vaccines, namely Pfizer-BioNTech’s Comirnaty and Moderna’s Spikevax, were successfully deployed to help control the SARS-CoV-2 pandemic, and their updated formulations continue to be recommended, albeit only for high-risk populations. One widely discussed aspect of these vaccines is their uniquely broad spectrum and increased incidence of adverse events (AEs), collectively referred to as post-vaccination syndrome (PVS). Although the reported PVS rate is low, the high number of administered doses among healthy individuals has resulted in a substantial number of reported vaccine-related injuries. A prominent manifestation of PVS is multisystem inflammation, hypothesized to result from the systemic transfection of organ cells with genetic instructions for a toxin, the spike protein, delivered with lipid nanoparticles (LNPs). In this narrative review, we focus on endothelial cells in the microcirculatory networks of various organs as primary sites of transfection with mRNA-LNP and consequent PVS. We outline the anatomical variations in the microcirculation contributing to the individual variability of symptoms and examine the molecular and cellular responses to vaccine nanoparticle exposure at the endothelial cell level with a focus on the pathways of a sustained cascade of toxic and autoimmune processes. A deeper understanding of the mechanisms underlying mRNA-LNP-induced AEs and PVS at the organ and cellular levels is critical for improving the safety of future vaccines and other therapeutic applications of this groundbreaking technology. Full article

(This article belongs to the Special Issue Population Immunity and Persistence to SARS-CoV-2 Induced by Infection and Vaccination, Protection Against New Infections and Implication for Further Vaccination: 2nd Edition)

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14 pages, 388 KiB

Open AccessArticle

Prevalence and Sociodemographic Factors Associated with Co-Vaccination Against Seasonal Influenza and COVID-19 and Reasons for Vaccine Hesitancy in the Albanian Adult Population

by Albana Fico, Gentiana Qirjako, Enkeleint A. Mechili, Eugena Tomini, Silvia Bino and Genc Burazeri

COVID 2025, 5(8), 132; https://doi.org/10.3390/covid5080132 (registering DOI) - 12 Aug 2025

Abstract

Background: Vaccination is a crucial public health measure to control infectious diseases, including seasonal influenza. Yet, vaccine uptake varies globally due to sociodemographic factors, misinformation, and access disparities. Objectives: The objective of this study was to assess the prevalence and sociodemographic factors associated with vaccination and the main reasons for vaccine hesitancy in Albania. Methods: A cross-sectional study, conducted in Albania in November–December 2021, included a sample of 1302 individuals aged ≥18 years (≈57% females; mean age: 38.3 ± 15.0 years; response rate: ≈87%). A structured questionnaire was administered inquiring about co-vaccination status against seasonal influenza and COVID-19, reasons for not being vaccinated, and sociodemographic characteristics of participants. Binary logistic regression was used to assess the association of co-vaccination status with sociodemographic factors. Results: Overall, about 28% of individuals were co-vaccinated against seasonal influenza and COVID-19 at least with one dose (25% in males vs. 29% in females; 22% among 18–24-year-olds vs. 54% among those aged ≥65 years). Independent positive and significant correlates of being co-vaccinated included older age (OR = 7.0, 95%CI = 3.7–12.9) and a higher educational attainment (OR = 2.3, 95%CI = 1.4–3.6). The main reasons for vaccine hesitancy among non-vaccinated individuals included the belief that vaccines are: harmful (72%), not effective (66%), weaken the immune system (58%), are not safe (56%), and preference to recover naturally (52%). Conclusions: This study evidenced a relatively low co-vaccination rate in Albania with significant sociodemographic disparities, notwithstanding the availability of vaccines and their free-of-charge provision to the overall population. Older age and higher educational attainment were identified as independent positive predictors of co-vaccination uptake, suggesting the need for targeted public health strategies to address vaccine hesitancy, particularly among younger and less-educated population categories. Our findings emphasize the importance of tailored communication campaigns and community-based interventions to improve vaccine coverage and mitigate the impact of infectious diseases in Albania and elsewhere. Full article

(This article belongs to the Section COVID Public Health and Epidemiology)

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12 pages, 2128 KiB

Open AccessArticle

Altered Gut Microbiota and Predicted Immune Dysregulation in Early Childhood SARS-CoV-2 Infection

by Dong Hyun Kim, Byung Ok Kwak and Ky Young Cho

Microorganisms 2025, 13(8), 1879; https://doi.org/10.3390/microorganisms13081879 (registering DOI) - 12 Aug 2025

Abstract

The gut microbiome plays a key role in immune regulation. Young children experience rapid microbiome development, yet data on its alteration during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection remain limited. This study aimed to characterize gut microbiome changes and immune-related pathway alterations in young children with coronavirus disease 2019 (COVID-19). Eighteen children under 2 years old with confirmed SARS-CoV-2 infection and seven healthy controls were enrolled between December 2021 and June 2022. Stool samples were analyzed using 16S rRNA gene sequencing. In children with COVID-19, the gut microbiome exhibited an increase in Bacteroidota and Bacillota, whereas Actinomycetota and Pseudomonadota were reduced, with higher abundances of Bifidobacterium, Escherichia, and Streptococcus and lower abundances of Faecalibacterium, Clostridium, and Ruminococcus compared with healthy controls. Children with COVID-19 exhibited reduced alpha diversity, indicating microbial dysbiosis, and significant differences in beta diversity compared with healthy controls. Predictive functional analysis revealed downregulation of key immune-related pathways, such as interleukin-17, NOD-like receptor, and Toll-like signaling, which may impact mucosal immunity and viral clearance in children with COVID-19. SARS-CoV-2 infection in early childhood is associated with gut dysbiosis and the suppression of key immune pathways. These findings highlight the potential long-term impact of early-life microbial disruptions on immune development. Full article

(This article belongs to the Section Gut Microbiota)

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21 pages, 763 KiB

Open AccessSystematic Review

Humoral and Cellular Immune Responses Against SARS-CoV-2 Following COVID-19 Vaccination in Older Adults: A Systematic Review

by Ruth Angélica Rojas-De la Cruz, Janeth M. Flores-Córdova, Cielo Cinthya Calderon-Hernandez, Nelson Luis Cahuapaza-Gutierrez, Nino Arturo Ccallalli-Ruiz and Fernando M. Runzer-Colmenares

Vaccines 2025, 13(8), 852; https://doi.org/10.3390/vaccines13080852 (registering DOI) - 12 Aug 2025

Abstract

Background: Evidence on the humoral and cellular immune responses to SARS-CoV-2 following COVID-19 vaccination in older adults is warranted. Aims: To synthesize and analyze the current evidence on humoral and cellular immune responses to both standard and booster COVID-19 vaccination in individuals aged 60 years and older. Methods: Clinical trials and observational studies were included. Reviews, case series, letters to the editor, and similar publications were excluded. A selective literature search was conducted in the following databases: PubMed, Scopus, EMBASE, and Web of Science. The risk of bias and methodological quality of the included studies were assessed using the Newcastle–Ottawa Scale (NOS) and the Risk of Bias 2.0 (RoB 2) tool. Statistical analysis was conducted using Stata version 18 and Review Manager version 5.4.1. Results: Thirteen studies were included: eleven observational studies and two randomized clinical trials, evaluating humoral and cellular immune responses in 782 older adults. Messenger RNA vaccines were the most administered, particularly Pfizer-BioNTech (76.9%) and Moderna mRNA-1273 (23%). In most cases, immune responses were assessed after the second dose and booster doses. Most studies (61.5%) reported increased IgG titers specific to the SARS-CoV-2 Spike protein, while 23.1% reported a decrease. Regarding cellular immunity, 46.2% of the studies reported low interferon-gamma (IFN-γ) levels post-vaccination, whereas 38.5% showed increases. These findings highlight the need for tailored vaccination strategies to address emerging variants, particularly in vulnerable populations such as older adults. Conclusions: In older adults receiving COVID-19 vaccination, humoral immunity tends to increase, whereas cellular responses are frequently diminished, reflecting age-related immunosenescence that may limit the durability and breadth of protection following vaccination in older adults. Full article

(This article belongs to the Special Issue Understanding Immune Responses to COVID-19 Vaccines)

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15 pages, 1144 KiB

Open AccessArticle

How Musculoskeletal Tumor Management Changed During the COVID-19 Pandemic: Data from a Nationwide Questionnaire Survey of Hospitals Specializing in Musculoskeletal Tumors in Japan

by Takeshi Morii, Shintaro Iwata, Kensaku Yamaga, Masanori Okamoto, Kosei Ando, Takaaki Tanaka and Jun Nishida

Curr. Oncol. 2025, 32(8), 453; https://doi.org/10.3390/curroncol32080453 (registering DOI) - 12 Aug 2025

Abstract

Background: While changes in clinical practice during the COVID-19 pandemic in Japan have been widely studied, data specific to bone and soft tissue tumor care remain limited. Methods: A nationwide web-based survey was conducted among hospitals specializing in musculoskeletal tumors. It assessed the occurrence of COVID-19-related events (patient infections, outbreak clusters, and staff infections), delays in referral and diagnosis, postponement or cancellation of specific treatments, and changes in institutional management strategies. Results: Seventy-eight hospitals (91.7% of all specialized centers) responded. Patient infections, outbreak clusters, and staff infections were reported by 28.2%, 48.7%, and 53.8% of hospitals, respectively. While radiological exams and biopsies were largely maintained, patient referrals decreased significantly. Surgical treatment was more affected than chemotherapy or radiotherapy. Strategy changes included surgery delays or cancellations (48.7%) and prolonged follow-up intervals (20.5%). Among COVID-19-related factors, only direct patient infections were significantly associated with institutional changes in treatment policy. Conclusions: The pandemic substantially disrupted outpatient services and surgical care in musculoskeletal oncology. Patient infection was the main driver of treatment strategy modifications. Full article

(This article belongs to the Special Issue The Evolving Role of Surgery in Multidisciplinary Care for Sarcoma Patients)

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23 pages, 1455 KiB

Open AccessArticle

COVID-19 and Its Aftermath on Pediatric Oral Health: A Study of Dental Caries and Hygiene in Romanian Children

by Maximilian Ilea, Alina-Ioana Forray, Nausica Bianca Petrescu, Ioana-Codruta Mirica, Alina Ormenişan, Mine Betül Üçtaşli, Adriana Melnic and Ondine Patricia Lucaciu

Children 2025, 12(8), 1061; https://doi.org/10.3390/children12081061 (registering DOI) - 12 Aug 2025

Abstract

Background/Objectives: Official data on the oral health of young children in Romania are limited, especially concerning the societal shifts following the COVID-19 pandemic. This study aimed to compare the oral health status, hygiene habits, diet, and dental care patterns of 6-year-old children in a rural Romanian region before and after the pandemic. Methods: A cross-sectional survey studied two groups of 6-year-olds from rural Transylvania: Group 1 (n = 77), assessed 2018–2020 pre-pandemic, and Group 2 (n = 136), assessed in 2024 post-pandemic. Clinical data used the Decayed, Missing, and Filled Teeth (DMFT) index. Parents completed questionnaires on oral hygiene, diet, dental visits, and pandemic-related topics for Group 2. Chi-square, Student’s t-tests, and a multiple linear regression were used to analyze the data. Results: Post-pandemic, 70% of children brushed twice daily, up from 26%. Despite this, negative outcomes increased: the number of affected teeth rose from 6.8% to 29.6% (p < 0.001), sugar intake increased, and dental visits became more reactive, with pain being the main reason for 61% of post-pandemic visits, compared to 17% pre-pandemic. Conclusions: This study reveals a significant oral health paradox: despite a three-fold increase in recommended toothbrushing, caries experience in permanent teeth increased four-fold. This outcome was driven by a high-risk environment of more cariogenic diets and reduced preventive care, with lower maternal education also identified as a key independent risk factor. These findings show that promoting hygiene alone is insufficient, underscoring the urgent need for public health programs that integrate nutritional counseling, improve access to preventive care, and address underlying socioeconomic disparities. Full article

(This article belongs to the Section Pediatric Dentistry & Oral Medicine)

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State-of-the-Art Webinars on COVID-19

WEBINAR 1: How to Avoid a New Lockdown?

The first webinar in the series, held on 17 April 2020, saw both Prof. Dr. Antoine Flahault, Director of the Institute of Global Health, University of Geneva, Switzerland, and Prof. Dr. Evelyne Bischof, Associate Professor, Shanghai University of Medicine and Health Sciences, Shanghai, China and Research physician, University Hospital of Basel, Basel, Switzerland speak on this topic.