Not sure what level of biology you topped out at, but there are viral infections and bacterial infections. Viral infections are not treated with antibiotics. Bacterial infections are treated with antibiotics.
Did I not read that the zpack creates an alkaline pH in your cells that inhibits the virus replication. I would look it up, but someone else can just as easily do that. The thing is the combination of the two is what is important.
I am not a physician - Masters in Microbiology and Biochemistry with virology - Retired from a near 50 year career in pharmaceutical manufacturing laboratory and QC/QA. Ended as VP of Quality with a drug company, and a general "know it all".
And a bit of wine tonight.
Edited to add - A week or two ago, a doctor would have prescribed this combination "Off Label" since there was no label indication of suitability/approval for use in this condition.
Most Doctors are very reluctant to prescribe Off Label use of drugs, since they take on considerable liability when they do such things. If I heard right, there is a big push within FDA to list the combination as acceptable for use in this emergency situation, which allows doctors to prescribe the drugs, even though there is not an acceptable amount of study to approve them as "safe and effective".
S&E are words taken directly from the Pure Food and Drug act. FDA has the responsibility for assuring drugs are S&E. They are not able to do this without a ton of data, which is not out there at the moment.
Maybe I'll add more later.