I dont think anyone here is going to know whether it is a breach of the 1st amendment until it hits the courts, which it will:
Here are some of the cases that coronavirus could conceivably send to the Supreme Court.
theweek.com
But as the article states, as it is not specifically targeting religion, but rather all gatherings, then it might not be a breach if the 1st amendment.
It just seems weird to me that the Bible is all about your fellow man and selflessness, yet people cant stop going to church for a few weeks in order to help flatten the curve and save lives. That to me is the opposite of what the teachings of the Bible are about.