I'm not sure, but isn't it the case that Bose-Einstein condensates have been created (a collection of super cooled particles) and shown to behave as if they were a single particle?
Specifically, haven't physicists achieved putting such a condensate in a superposition? Wouldn't that count as a larger scale demonstration of superposition?
I can see that a virus is going to be much more complex than a bunch of uniform particles, but why should scale matter whether superposition is possible? Don't all objects experience some level of superpostion, only it occurs for immeasurably small time periods before wave collapse?