The closest star to Earth, other than our Sun, is Proxima Centauri, 4.24 light years away, which is binary paired with Alpha Centauri, which is 4.34 light years away. PC is a red dwarf, and so could not go supernova. AC is about the size of our Sun, which also means that it could not go supernova. The closest star to us that could go supernova is Spica, which is 260 light years away, and a supernova would have to be about 50-100 light years away to cause us harm.
Another thing is that you said the scientists "detected" it before its effects got to us. The supernova's effects would travel at the speed of light, so we wouldn't be able to detect it before it reached us and killed us.