To determine whether you can and should still exercise during sickness, it really depends on your symptoms. As a rule of thumb, if your symptoms are above the neck (i.e. a runny nose, sore throat and/or blocked sinuses) you are probably okay to still do some resistance training.
However, you will likely need to lower the intensity, reduce the number of sets you perform and increase your rest periods. Performing some milder resistance training may actually help to circulate healing nutrients and amino acids around the body and flush out toxins.
Plus, it will give you a sense of control over your body as you’ll be doing something active, rather than sitting on the couch watching daytime TV soapies.
If, however, your symptoms are from the neck down (i.e. heavy lungs, joint aches, fever, diarrhoea, vomiting and/or lost appetite) you will likely benefit from taking a complete break from all resistance exercise until your symptoms improve.
I recommend you give any sort of cardiovascular exercise a miss, regardless of your symptoms, as you will likely find it hard to breathe and regulate your body temperature.
However, a slow stroll in the sunshine and fresh air will likely make you feel better and speed up the recovery process.
As always though, be sure to consult your GP if your symptoms worsen or don’t improve after a few days.