I don't think it's taken very long for coronavirus to hit the east coast. There are plenty of people who are carriers and don't realize it because they don't have symptoms (yet). On top of that, sometimes coronavirus just appears like a regular common cold, so people don't go to the doctors about that. Furthermore, the U.S. is doing a terrible job with testing people for coronavirus. They started off with faulty tests and now there is a limited number of (working) tests available, but only in SOME states. They're not even testing people until it gets severe (which is obviously a bad move on their part). That happened to a coronavirus guy in Washington state where he went to an ICU and the doctors waited FOUR DAYS to test him for coronavirus! They probably wouldn't have even tested him for it had he recovered in that four day time span. So, they probably would've just (mistakenly) called it the flu upon discharge. And I bet that's happening right now. Things are probably being called the "flu" when it's actually coronavirus.

But anyway, I think coronavirus has been on the east coast for at least 2-3 weeks. There are lots of flights going from LAX to BOS or JFK everyday, as both are very popular destinations. I wouldn't be surprised if someone from China came to California before the Feb 2nd ban, infected a bunch of people there (because we are seeing lots of infections in California right now), and then that those people traveled to NYC or Boston without knowing they had coronavirus. Incubation is 14 days, with some doctors saying it's even longer at 27 days. It's been just over 27 days since we banned China flights, so if we assume the worst that incubation is 27 days, about now is the right time to be seeing people exhibit coronavirus symptoms.

IMO, it's only going to get worse. Not to be a Debbie downer, but technically speaking, the only possible way we could have stopped the spread in the U.S. was if we banned all international travel back in December/January when China first reported the coronavirus outbreak. I'm not saying that is a "reasonable" solution, but I think that's the only thing that could have worked because now we have irresponsible countries like Italy and South Korea who didn't take the outbreak seriously and are now spreading it everywhere. So for the time being, just stay away from people, use lots of hand sanitizer, and wash your hands for 20+ seconds. Masks only stop YOU from spreading your germs; they don't stop you from getting someone else's.