Careful with orthomolecular. It's touted as a 'peer reviewed science journal' but it's really just a pseudo science/conspiracy site used to push all those dietary supplements you see on fake news sites.
The Author (Andrew Saul) is absolutely a fraud.
The bottom line, the body needs Vitamin C daily, can not store large amounts, and to much of it will test the fast trousers drooping skills.
The US National Library of Medicine, National Institutes of Health
The effects of vitamin C against infections should be investigated further
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5409678/As for
Vitamin D (Sun),
An estimated one billion people worldwide are either vitamin D insufficient or deficient
Blood pressure pills (ACE inhibitors) may be making people die from Coronavirus
Several observational studies, which track participants over time without assigning a specific treatment, have associated low vitamin D levels with greater susceptibility to acute respiratory infections.
https://news.harvard.edu/gazette/story/2017/02/study-confirms-vitamin-d-protects-against-cold-and-flu/Since at this time of the year, the lack of vitamin D in the population of the northern hemisphere is widely observed, quasi exhibits a pandemic, it is likely that the role of RAS in COVID-19 disease is not negligible. Indeed the world distribution of COVID-19 fatalities appears to well overlap with that of the vitamin D lacking population. Not to mention that people lacking vitamin D have a weaker innate immune defense against SARS-CoV-2.
https://www.bmj.com/content/368/bmj.m810/rr-24