Here are a couple of the very precise references, out of many others since the onset of the virus:
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Ruben Manuel Luciano Colunga Biancatelli,1,2,3,* Max Berrill,4 John D. Catravas,1,2,5 and Paul E. Marik1
Front Immunol. 2020; 11: 1451.
Published online 2020 Jun 19. doi: 10.3389/fimmu.2020.01451
PMCID: PMC7318306
PMID: 32636851
Abstract
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Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) represents an emergent global threat which is straining worldwide healthcare capacity. As of May 27th, the disease caused by SARS-CoV-2 (COVID-19) has resulted in more than 340,000 deaths worldwide, with 100,000 deaths in the US alone. It is imperative to study and develop pharmacological treatments suitable for the prevention and treatment of COVID-19. Ascorbic acid is a crucial vitamin necessary for the correct functioning of the immune system. It plays a role in stress response and has shown promising results when administered to the critically ill. Quercetin is a well-known flavonoid whose antiviral properties have been investigated in numerous studies. There is evidence that vitamin C and quercetin co-administration exerts a synergistic antiviral action due to overlapping antiviral and immunomodulatory properties and the capacity of ascorbate to recycle quercetin, increasing its efficacy. Safe, cheap interventions which have a sound biological rationale should be prioritized for experimental use in the current context of a global health pandemic. We present the current evidence for the use of vitamin C and quercetin both for prophylaxis in high-risk populations and for the treatment of COVID-19 patients as an adjunct to promising pharmacological agents such as Remdesivir or convalescent plasma.
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Leon Margolin, MD, PhD https://orcid.org/0000-0002-0642-300X md@cpmiohio.com, Jeremy Luchins, PhD https://orcid.org/0000-0003-2806-6872, […], and Sanford Lefkowitz, MSc
Journal of Evidence-Based Integrative Medicine
Research article, First published online July 6, 2021
Abstract
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Objectives and Setting.***********
As the lethal COVID-19 pandemic enters its second year, the need for effective modalities of alleviation remains urgent. This includes modalities that can readily be used by the public to reduce disease spread and severity. Such preventive measures and early-stage treatments may temper the immediacy of demand for advanced anti-COVID measures (drugs, antibodies, vaccines) and help relieve strain also on other health system resources.
Design and Participants.
We present results of a clinical study with a multi-component OTC “core formulation” regimen used in a multiply exposed adult population. Analysis of clinical outcome data from our sample of over 100 subjects − comprised of roughly equal sized regimen-compliant (test) and non-compliant (control) groups meeting equivalent inclusion criteria − demonstrates a strong statistical significance in favor of use of the core formulations.
Results.
While both groups were moderate in size, the difference between them in outcomes over the 20-week study period was large and stark: Just under 4% of the compliant test group presented flu-like symptoms, but none of the test group was COVID-positive; whereas 20% of the non-compliant control group presented flu-like symptoms, three-quarters of whom (15% overall of the control group) were COVID-positive.
Conclusions.
Offering a low cost, readily implemented anti-viral approach, the study regimen may serve, at the least, as a stopgap modality and, perhaps, as a useful tool in combatting the pandemic.
My experience has been that once I contracted the virus unbeknowingly from a close friend who was giving me transportation, for which the effects lasted only two and a half days, with no other aftereffects. Otherwise, no other incidents or symptoms characteristic of COVID-19.
That is not a research paper. It is a review which collates the findings of previous research in order to present the hypothesis that quercetin and vitamin C might be efficacious against Covid. It does not constitute pre-clinical in vitro, cell culture, or animal studies and certainly is no substitute for rigorous clinical studies in humans. The FDA would never give market approval for the use of quercetin with vitamin C to treat Covid based on this extremely limited review that has no clinical or animal data to back it up.
I previously discussed limitations of this paper in my reply #11 to this thread, but apparently messed up on the link.
20-Week Study of Clinical Outcomes of Over-the-Counter COVID-19 Prophylaxis and Treatment
This paper has a number of limitations.
First, it does not show the usual indicator of peer-review. It shows a "published online" date, but does not show the date it was received or the date it was received in revised form or an acceptance date. Peer-reviewed articles usually show three or four different dates. I doubt that the authors would be able to get this published in any peer-reviewed journal.
Second, the size of the study (113 subjects split between control and study groups) is extremely small, too small for any robust statistical analysis. Clinical studies with high statistical power usually include several hundred, usually over a thousand patients.
Note: the statistical weakness of this "study" was apparently noticed by other readers, since the authors issued the linked explanation of their statistical method a few months later. Benefit of OTC Formula Against COVID-19—Statistical Analysis Explained. The explanation is not very convincing, either, to anyone who is familiar with the types of statistical analysis used in clinical studies.
Third, the outcome measure was whether people caught Covid or not. The study did not examine treatment outcomes in patients who actually had Covid and no conclusions on the efficacy of the protocol described can be made based on the data provided.
This one sentence from the linked paper encapsulates the problem: At an interim evaluation point of 5 weeks after implementation of the protocols, the only clinical and/or test-confirmed cases of COVID-19 arose in the non-compliant control group; on the other hand, none of the regimen-compliant subjects presented with symptoms of any viral illness.
The study was non-blinded and patients basically self-selected to be in one group or the other. The difference in whether or not they caught Covid is most likely explained by behavior. Those who were in the "compliant" group were probably more concerned about their health overall and likely took other measures to avoid Covid, such as diligent use of masks and avoiding being around other people unless absolutely necessary. And those in the "non-compliant" group probably were less concerned about Covid and took more risks.
Fourth: none of the authors have experience in medical (especially infectious disease) research. They are all affiliated with the Comprehensive Pain Management Institute, LLC, Columbus, OH. Pain management is a different specialty than infectious disease. Furthermore, medical research is very different from the practice of medicine. Their lack of experience explains why this paper is of such poor quality.
I will end the analysis here.
Disclaimer: I am purposely open about my sources so that anyone who wishes to debunk me can look at the sources and explain exactly how I misrepresented them, how the sources themselves are suspect, or how I outright lied. (No one has debunked me yet.)