colloidial silver is the only thing that actually works
vitamin C can shorten the duration of a virus too but you shoudl already be consuming all your vitamins and minerals through heealthy eating
besides 'taking something' you should implement fasting and rest. when an animal is sick it will lay out and not eat for a period of time to allow the body to fight off the issue.
It is really about prevention. The best thing to do is to eat a variety of colours of fruits and veggies. That will ensure you get all the vitamins, minerals, and antioxidants you need.