This study of critically ill patients with COVID-19 found that giving patients vitamin B1 (thiamine) reduced in-hospital mortality and 30-day ICU mortality each by over 50%. Thiamine also reduced risk of thrombosis during ICU stay by 81%.  Link to PDF of Study
“Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system.” [Wikipedia] In patients with severe Covid-19, thrombosis can damage major organs and can cause death. Reduction of risk of thrombosis is important to treating patients and reducing deaths from Covid-19.
The dosage of thiamine used on patients varied from 50 mg/day to 200 mg/day. Thiamine (B1) is used as one medication to treat sepsis in the ICU. It is also part of the MATH+ protocol.
Study: “There were 14 patients (18.4%) who died during ICU stay among the thiamine group, compared with 29 patients (38.7%) in the other group. In other words, patients who used thiamine as adjunctive therapy during ICU stay had a lower 30-day ICU mortality by 55% (OR (95% CI): 0.45 (0.22, 0.94), p-value = 0.03) (Table 1). Additionally, thiamine use was associated significantly with a lower in-hospital mortality by 51% (OR (95% CI): 0.49 (0.25 ,0.97), p-value = 0.04). The overall survival probabilities were higher during hospital stay among patients who received thiamine before and after propensity score-matched (Fig. 1a, 1b).” 
Reducing deaths in-hospital and in the ICU from severe Covid-19 is a high priority during this pandemic. Already more than 5 million persons have died from Covid-19 since the pandemic began. Thiamine is a commonly available vitamin (B1) and is safe at the above tested dosing (50 to 200 mg/day). There is no reason to withhold thiamine from Covid-19 patients, as the likelihood of a strong benefit is established, and the vitamin is safe and well-tolerated, even at high dosing.
Study: “Only 2 (2.4%) patients who received thiamine developed thrombosis during ICU stay, compared with 9 (11.1%) patients in the non-thiamine group. Patients who received thiamine as an adjunctive therapy were less likely to have thrombosis during ICU stay as compared to patients who did not (OR (95% CI): 0.19 (0.040, 0.884), p-value = 0.03).” 
Thrombosis is a serious complication of severe Covid-19, which can damage or destroy organs and can cause death. The study authors were not certain how thiamine reduced thrombosis by 81%, but the results were statistically significant. Again, the benefits are very substantial, and the downside is almost non-existent.
The study authors concluded the following: “Thiamine use as adjunctive therapy may have potential survival bene¦ts in critically ill patients with COVID-19.”
Ronald L. Conte Jr.
an author, not a doctor
1. Al Sulaiman, Khalid, et al. “Evaluation of Thiamine as Adjunctive Therapy in COVID-19 Critically Ill Patients: A Multicenter Propensity Score Matched Study.” (2021).
Link to PDF of Study