The vaccine isn't 100% effective and some people have weaked immune systems. Some people are infected with a massive dose of virus and some with a lesser dose. Some are infected with more than one variant at the same time and some might be dealing with an underlying condition.
This is why hygiene, wearing masks and social distancing is so important until we reach herd inmunity. But try to explain that to somebody capable of pulling a knife on you for a fiver.
My wife caught me wearing ladies underwear and threatened to leave me.
So I packed up all her clothes
And left.