Very nice.
Why is the RAT only indicative of past infection? Won’t it show up on anyone whose body is naturally immune?
A different question: what kind of scan might be capable of identifying the particular antibodies* without drawing blood? Are there any organs (like, for instance, the eyeballs) where blood is sufficiently visible that a particular very small wavelength reflection might positively identify singular antibodies?
Such a test might then be generalised in nature, allowing ordinary people to be instantly scanned for any kind of infection that normally produces antibodies (whether or not an epidemic is already in progress), thus building up an immunity profile.