It depends on interpretation and I think conclusions are unclear from that graph. Try this: shift the blue curve about 15 days to the left. We may then interpr

It depends on interpretation and I think conclusions are unclear from that graph. Try this: shift the blue curve about 15 days to the left. We may then interpret masks acted in lowering the infection peak, since masks were introduced at an earlier infection stage. In other words, if St Louis reinstated masks at the same infection count as Missouri it might have seen a higher infection peak.