The difference is here, without the graph, the message is much like, "you may have been infected, but, since you're showing no symptoms, probably not", whereas

The difference is here, without the graph, the message is much like, "you may have been infected, but, since you're showing no symptoms, probably not", whereas with the graph it's probably much more like, "you have been identified as a likely spreader of the virus". There's a subtle difference in the call to action.