To say Elderberry is a "fad" is pretty ignorant considering it has numerous scientific studies and a well known Mechanism of Action against viruses, namely blocking the receptor which many viruses target to gain entry into human cells, not to mention many trials IN PEOPLE showing its effectiveness.
Here is one...plenty of others you can find all show the same thing, at least 20...its highly effective against many viruses because it prevents them from replicating.
Elderberry has been used in folk medicine for centuries to treat influenza, colds and sinusitis, and has been reported to have antiviral activity against influenza and herpes simplex. We investigated the efficacy and safety of oral elderberry syrup for treating influenza A and B infections...
pubmed.ncbi.nlm.nih.gov
Astaxanthin has been cited as being used effectively in people during the COVID-19 outbreak to tamp down the over release of inflammatory cytokine IL-6 which is the main reason people end up in the ICU, on ventilators or dead...the body basically ends up generating an over aggressive immune system response that kills them...Astaxanthin has been found to regulate the immune response to prevent this from happening in many cases..
Cardax seeking strategic collaborations to further develop astaxanthin for COVID-19 (OTCQB:CDXI) today released a white paper outlining the potential role of astaxanthin in the treatment of coronavirus disease and is seeking strategic collaborations to further develop astaxanthin for COVID-19. The
www.biospace.com
Vitamin D is basically what controls your immune system regulation via gene expression and its strength along with your gut bacteria. Vitamin D allows for production of cathelicidin which is your bodies "seek and destroy" missile used by macrophages against infections. The more Vitamin D, the more cathelicidin, the more "shots" your body has to use. Vitamin D isn't a vitamin at all its actually a hormone.
Cathelicidin antimicrobial peptide is an important mediator of the innate immune response. In addition to its potent antimicrobial activity, cathelicidin has been shown to have chemoattractant and angiogenic properties. Recent research has demonstrated ...
www.ncbi.nlm.nih.gov
And yes I know about needing Vitamin K2/A with high dose Vitamin D if you are taking it for a long time..short term you should be fine.
Once you educate yourself a little more so you can talk from a place of knowledge rather than ignorance we can have a better discussion.