It really depends on the severity and the other symptoms. I was recently sick (flu, cough, sore throat) for a week and my doctor advised that the first 3 days, perhaps it’s good to eat and give myself some nutrition to hold off other symptoms. I stopped fasting for 2 days, ate maintenance and went back to it on the 3rd day even though I was still feeling sick and on meds.
I don’t change for my fast unless it’s impactful to sleep enough where I need NyQuil because sleep is so important. When I’m sick I’ll skip exercise and make sure I’m not in too much of a caloric deficit
Listen to your body when you’re sick. Most of the time when we get the flu, our bodies don’t feel like eating anyway. If you want to eat, eat. If not, don’t. Now is not the time to keep fasting. Get better soon!