The Ra”n explains: If the father or the husband confirmed the neder and asked on that same day that the confirmation should be annulled, can it be annulled (similar to a neder)? It is obvious that it cannot be annulled on the following day, for it has no less effect than remaining quiet.
It is evident from the Ra”n here and he says so explicitly in Kesuvos that there is certainly no annulment if he had remained quiet.
The Reshash asks: What is the distinction? If he can annul a spoken-out confirmation, why can’t he annul a confirmation that came about because he remained quiet (which is regarded automatically as a confirmation)?
The Steipler Gaon answers: An annulment is only possible on an action performed by a person; however, remaining quiet, although that is deemed a confirmation, is not an action that can be annulled.