D-3. I doesn’t much matter whence th flu or cold originates. Take the D-3 supps and you will not get the viruses. 5000 i.u. a day seems to be an effective amount- les perhaps, more certainly. The reason Flu etc. is almost entirely a winter phenomenon is the lack of sunshine on the skin.
We’ve been doing that for years. My daughter was on anti-seizure med that stripped her of Vitamin D.
Unfortunately, my kids still got sick.