to 2+ more and a few people here or there just outside the metro center are infected it is still going to spread back into the city... and some in the city are already infected.
It will likely slow the spread, though, and that's an important thing. From what they're saying if left to spread naturally the peak would hit like a tsunami. Slowing it down spreads it out over more time... hopefully enough to keep it from overwhelming the medical system.
The link from below had some pretty good animations showing how social distancing can have a major impact on the speed it spreads.
https://www.washingtonpost.com/graphics/2020/world/corona-simulator/