Based on my spotty but self-interested knowledge of medical history, we make new immune related drugs for mostly three reasons: one, microbes have adapted and w

Based on my spotty but self-interested knowledge of medical history, we make new immune related drugs for mostly three reasons: one, microbes have adapted and we need to alter the chemical to still be effective (see also quinine and pyrethrins), two, to simplify production (yew trees vs lab made Taxol), or more cynically, to get a new patent on a drug and keep making money after you’ve run the initial patent and the time released variant clocks out (I absolutely hate that that’s a thing). So while it’s not surprising that a new flavor in a class of drugs is also expensive, it’s not a foregone conclusion. A new catalyst or a less tricky bond to force could make a drug that works as well or almost but is much cheaper to make.