Vaccines

The twentieth entry is a perda gradual de imunidade, and Portuguese states it in the plainest way available: a gradual loss. English reaches instead for a word that has been watching the sky since Old English, and calls the same thing « waning immunity ». « To wane » is what a moon does when it shrinks night after night, the opposite of « to wax », and the verb carries the whole shape of the process with it: not a loss at a stroke but a slow, continuous, foreseeable falling away that can be measured long before anybody feels it. That is exactly what an antibody titre does after a second dose, which is why the image settled into the technical literature and why « waning » now appears in trial reports with no hint of poetry left in it. Two consequences follow for anyone translating. « Waning » is almost never said of something that could simply stop, so it will not stand in for « loss » in general. And the Portuguese phrase, having no picture inside it, needs the adjective gradual to say what our verb says on its own.