Why is covid different than any other disease?

This reference

https://www.biopharma-reporter.com/Article/20...xclusivity

seems to say that the FDA grants 12 year marketing exclusivity from the date of first approval of the drug in any disease.

The reference seems to say that the second disease you get approved for is guaranteed to have less than 12 year marketing exclusivity because the 12 year clock started with the approval of the first disease.

The reference says that the only way to restart the 12 year clock is if the drug itself is modified for the second disease, like a molecular difference.

If my reading of the reference is correct, then drugs like leronlimab, which work without modification for many diseases, are profit maximized when all of the diseases are approved at the same time.

So for example if leronlimab is quickly approved for covid and then for cancer three years later, the cancer marketing exclusivity would only get nine years.

I dont understand why covid approval would not start the cancer exclusivity clock.

Even more confusing to me are US patents for the same drug in different diseases.

Its my understanding that US patents expire in 17 years.

Presumably the leronlimab molecule was patented many years ago. The patent on the molecule may have ten years or less to expiration.

But then a patent for leronlimab for covid has more than 17 years left because the c0vid patent is not yet issued.