She knew it was not by explanations and counter-charges that she could ever hope to recover her lost standing; but even had she felt the least trust in their efficacy, she would still have been held back by the feeling which had kept her from defending herself to Gerty Farish—a feeling that was half pride and half humiliation.
There are no more uses of "efficacy" in the book.
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The doctor weighed the efficacy of each treatment against potential side-effects.
They held hearings to investigate concerns about the safety and efficacy of the vaccine.