Why do you hate antivaxxers - are you trained in medicine, molecular biology, etc. or is this nothing more than orthodox ideological position?
The scientific method and science itself is NEVER SETTLED. And it is always advanced from discussion including anecdotes that become more formal research.
Niacin appears to be very well studied, but not in the context of post-viral illnesses. But there are a mountain of papers which may help to explain why it works. Here are a few:
Underlying lack of niacin and establish indicated use: https://academic.oup.com/bib/article/22/2/1279/5964187 https://clinmedjournals.org/articles/jide/journal-of-infecti...
Lipids in covid: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7869689/ Sars CoV 2 entry to cells: https://www.nature.com/articles/s42255-020-00324-0 Replication etc: https://journals.plos.org/plospathogens/article?id=10.1371/j... Nicotinic acid’s effects on lipids: https://www.eurekaselect.com/126340/article