Japanese term (edited): 有効率(ウイルスが完全に駆除される率）

有効率 by itself would seem to be the same as "response rate" in English. However, by itself, "response rate" is quite vague, and only means "the ratio of cases where the treatment causes the desired beneficial effect."

In this case, the source text goes on to specify ウイルスが完全に駆除される率, which shows that the desired response is a complete antiviral effect.

This might also be called "effectiveness rate" or "efficacy rate". However I don't think it would be translated as "efficiency rate".