At first, this still looks pretty familiar. The red curve goes up, and the green line starts to fall. But then you notice something unusual. The green curve suddenly has a small bend in it. That tells you that something else is affecting the outbreak. And now you can see what it is. The purple curve shows the vaccinated group. At the start, there are only a few, but as the outbreak goes on, more and more people move into that compartment. That means fewer people are left who can still catch the disease. And that is exactly what explains the bend in the green curve. At the end of the day, vaccination slows the wave down quite clearly.
