Descriptive, retrospective, observational, anonymous, study to evaluate the potential effect of incorporating calcifediol into the therapeutic protocol of patients hospitalized for COVID-19 on mortality and other outcome variables, such as admission to the Intensive Care Unit (ICU), to "Complejo Hospitalario Universitario de Albacete" (CHUA). Albacete (Spain)", based on the files of the MXXI medical records, Information System of the Laboratory (ISL) and Pharmacy.

The coronavirus disease-19 (COVID-19) pandemic, caused by the severe acute respiratory syndrome β-coronavirus (SARS-CoV-2), is one of the greatest challenges facing modern medicine and public health systems worldwide. Since its appearance in December 2019, it has caused nearly 7 million deaths, recognized, and confirmed worldwide, with high acute and post-acute morbidity, making it one of the deadliest in human history, with a devastating impact on national economies worldwide.

In the first outbreaks of COVID-19, although 80% were asymptomatic or had mild symptoms, 20% of patients developed severe symptoms, and 5% presented acute respiratory distress syndrome (ARDS), septic shock and accompanied multi-organ organ failure, with a high risk of death. Numerous risk factors have been described that influence the poor outcome of these patients, such as age, sex, high blood pressure, chronic obstructive pulmonary disease, diabetes, obesity, chronic lung and digestive diseases, asthma, chronic heart disease, cancer, D-dimer greater than 1000, or a high SOFA (Sequential Organ Failure Assessment Score). It has also been observed that patients with no a priori risk factors may have a poor outcome.

The scientific community immediately proposed strong social containment measures, quickly developed effective vaccines to prevent the appearance of severe clinical forms of COVID-19, and developed new treatments against all aspects of the disease: antiviral agents, anti-inflammatory agents, antithrombotic therapies, therapies against hypoxemic acute respiratory failure, therapies with anti-SARS-CoV-2 antibodies (neutralizing), modulators of the renin-angiotensin-aldosterone system and vitamins, so that social and economic activity has gradually recovered worldwide.

However, at the current time, there are some indications that hospital admissions for COVID-19 are on the rise again, so the pandemic seems far from over and future waves of infection are likely. These indications update and highlight again the repositioning strategy used since the beginning of the pandemic for the use of safe drugs, approved for another indication, and redirected to improve symptoms and clinical outcomes in patients with COVID-19. Various drugs have been investigated under this strategy and many studies have been published, some of them successful.

In this sense, during the first months of the pandemic, on the basis of biological plausibility, the investigators thought that the activation of the vitamin D receptor (VDR) signaling pathway of the vitamin D endocrine system (VDES) could produce beneficial effects in COVID-19. These effects were achieved by improving innate antiviral effector mechanisms, facilitating the induction of antimicrobial peptides/autophagy, mitigating the subsequent reactive hyperinflammatory phase of the host, decreasing the cytokine/chemokine storm, modulating the expression of the renin angiotensin system (RAAS) and neutrophil activity, maintaining the integrity of the pulmonary/intestinal epithelial barrier, stimulating epithelial repair and directly and indirectly reducing the increase in coagulability and prothrombotic tendency associated with a severe course of COVID-19 and its complications. Available evidence suggests that VDES/VDR stimulation, while maintaining optimal serum 25-hydroxyvitamin D [(25(OH)D)] status, in patients with SARS-CoV-2 infection may significantly reduce the risk of distress syndrome, acute respiratory distress syndrome (ARDS) and the development of severe COVID-19.

The investigators decided to use calcifediol, which is a prohormone (and cornerstone of the VDES) and substrate for the synthesis of the system's hormone, calcitriol. The poor availability of calcifediol described in the general population, most marked in patients affected by COVID, means that the potential protection that VDR/VDES stimulation confers against various aspects of the disease is lost.

Calcifediol provides pharmacokinetic advantages, which give it a certain functional superiority over native vitamin D3 and even over the hormonal form of VDES, calcitriol, for its use in COVID-19. It is very hydrophilic and, therefore, after oral ingestion, it is absorbed through the portal venous system and does not require hydroxylation at the 25 position, immediately increasing optimal circulating concentrations of 25(OH)D3. Therefore, even if administered orally, it is available at high concentrations within a few hours, and in a stable manner, to be a substrate for calcitriol synthesis at the kidney and other target organs in COVID-19.

The clinical trial pilot study and several observational intervention studies using relatively high doses of calcifediol (0.532 µg on day 1 and 0.266 µg on days 3, 7, 14, 21 and 28) decreased the severity of the disease, dramatically reducing the need for ICU admission, severity, and mortality rate.

Therefore, using calcifediol at the doses described for rapid correction of 25(OH)D deficiency in all patients in the early stages of COVID-19, in association with the best available therapy, was assessed as a good option for the treatment of COVID-19. For this reason, on January 24, 2021, the CHUA incorporated calcifediol into the protocol "Recommendations for action and treatment of the coronavirus SARS-CoV-2 disease" (COVID-19) version 11.1".

Inclusion Criteria:

1. Admitted to the hospital CHUA
2. Meet the SARS-CoV-2 diagnostic criteria with positive PCR
3. They have completed at least the first dose of Calcifediol within the first 72 hours after admission, (according to protocol).

Exclusion Criteria:

1. Patients who do not receive the full first dose of Calcifediol within the first 72 hours.
2. Patients for whom electronic medical record data cannot be collected.
3. Patients with other serious intercurrent diseases (eg advanced oncological pathology).

Patients admitted to the CHUA, due to COVID-19 [respiratory infection confirmed by radiographic pattern of viral pneumonia and positive PCR/antigen for SARS-CoV-2]. Those participants for whom there is not enough information in the files to be able to analyze the study hypotheses will be excluded from the study.

Patients meeting ALL inclusion criteria and NO exclusion criteria will be included in the study.

Anonymized information collected from patients will be shared publicly upon request. All information related to variables or results included in the study will be shared.

Data will be made available in the following months after all results will have been published.

All data requests will be reviewed by the principal investigator of the project. Data will be shared upon reasonable request to be examined or reviewed. It will not be permitted to carry out any other kind of study (including statistical) by people other than the researchers of the main study.