Does self isolation period restart?

[Mumof2mix]

If a person ( 1 vacvine only) is self isolating as a household contact of person with COVID and then another person at home tests positive does the person have to self isolate for extra days or it's 10 days from contact with first positive person ? The guidance is not clear.

As far as I know the original isolation period is not extended by another person in the household testing positive. This was the case when vaccines weren't about