I'm not an economist but "prone" in this case refers to something having a certain tendency. Being "prone" to something can be used for just about anything. A person who is physically not coordinated can be accident prone. Certain characteristics of an economy can make it "prone" to recession. Someone might have a reputation for being prone to cheating. Certain careers might be prone to early burnout such as healthcare workers. Does that help?

The phrase is unusual and metaphorical. It is not saying that the economies are prone *to* any particular thing. It is saying that the economies are prone as in lying down - knocked off their feet by the pandemic.