vampires are not invinsable they can die by bullet or stake the reason that we are able to live so long is because our bodies do not have to use energy to break down food into energy that it needs to function, we take the already broken down protien that is in your blood for our bodies it is easy for our bodies to digest because it has already been broken down, this alows our bodies to spend less energy getting what we need to live and in turn our bodies are less overworked and can last longer.