Most likely Acon, but might just also be NuxV if the patient is irritable.
I can't be sure, because in different patients, the same bug can need different remedies.
Both Acon and Nux are complementary to Sulph, so neither remedy would be problematic in relation to the proposed constitutional treatment to follow.
If you want to give a remedy at the first sign, Acon 30 is my first choice. If that works for a bit and then symptoms threaten again, you could try Acon 200.

I second that one Anna. I started with a cold yesterday and took 2 doses of Aconite. There is no hint of a cold today!! I have to admit that I did go outside in the cold for a run yesterday, hence the Aconite as opposed to anything else!!

Hi,
My younger daughter (infant eczema thread) had shown a recurrence of rash and was following GMs instructions, but halfway through it, i.e. by saturday noon she started showing the first signs (cough) of the viral infection so i decided to wait. I didnt give aconite since she hadn't been outside since christmas day. By mid night she developed a fever and her cough is become worse. She now cries when she coughs. Apetite has decreased a bit but not disappeared. The fever comes and goes. I have not given any medication. She has a clear runny nose. The cough so far is not productive. She is happy as long as she is being held or we are nearby. She is still alert and interested in toys and playing by herself for short intervals. We flew back from my sisters house early this (sunday) morning and she was fine through the journey. We did make a short trip outside yesterday evening but this was after she started coughing.

I have posted this in the infant eczema thread too. I was almost ready to give her Tub CM for her rash when the first sign of this occurred, so I waited on that.
Sarah
Sarah