、！
Oh, then the one from a year ago doesn't work anymore!
Literal
Well, 1 year before [of-の] [topic-は] already effect not-exist [explanatory-んだ]!
Realization in response to new information. じゃ is a casual connective 'well then, in that case,' used to introduce a conclusion. １年前の 'the one from a year ago' uses の as a substitute for a previously-mentioned noun (probably a medicine or product). 効き目 'effect, efficacy' is specifically used for the effectiveness of medicines, drugs, or treatments. もう...ない 'no longer' marks the lapse of a previous state. んだ gives the sentence an explanatory, realization-tinged ending.