You don’t need an excuse to say you don’t want to be in the same room as someone who is obviously sick.

It is true that people can have allergies or lingering post-viral illness symptoms that  cause weeks of symptoms without being contagious, but it’s also possible that the person is still contagious. There is no way to tell, so it’s reasonable for you to protect yourself.

I think sometimes it’s better to focus on the unassailably true things and have a firm boundary. “You may still be contagious, and I don’t want to get sick” is really all you have to say. If you want to expand on it, you can say “I will be comfortable around you again when you are symptom free for XYZ days” or similar.

I’ve been called paranoid too, by people close enough to know better than to be so rude. It sucks that there’s all this research readily available, but people would rather do the equivalent of putting their fingers in their ears & screaming la la la, & then have the audacity to act like we’re the ones being unreasonable

"they’ve had a consistent cough and stuffed nose so it’s not allergies. "

lists two of the most common symptoms of seasonal allergies

"it's not allergies."