How advanced was medicine in the Terran Federation several centuries
into the Atomic Era?

Specifically, first contact with Freya. A population essentially
identical to Terran humans.

So what didn't happen with a virgin field for Terran diseases? No
epidemics comparable to Spaniards encountering the Aztecs and other
tribes. Did the Terran Federation have universal antibiotics and
antivirals, even though unmentioned?

Of course, it is depressing to imagine what Calvin Morrison brought
along with him to Hostigos.