I’ve studied bio defense for years.
The correct distribution tool for a contagious virus is an infected human. Of which China has plenty of raw material.
High altitude dispersal is a ridiculous idea.
These balloons or whatever else they are sending are evidence of hostile intent and stopping them is important - but they are a very, very unlikely means of biological attack.
I said precisely what you initially said. Get a thousand sick Chinamen to fly all over the country.
People get sick, and there is no direct blame either.