My wife and I never did either.
We got either a flu or covid, don’t know which, a week or two ago.
Mine lasted 4 days, was fairly mild like a strong cold, and it was over, my wife’s a 10 day ordeal but she’s over it.
But I take 5000 IU’s of D3 every day along with several other supplements, my wife doesn’t, as she hates pills of any kind...........
I never get the flu and never get the flu shots. I only get a mild cold once every few years. My immune system just works very well I guess.
There is liquid vit d3...but she shd take k with it, and that may be hard to find in liquid form...