Why is the Delta variant so virulent in the US?

The figure is so staggering I can hardly believe it. But 80 million Americans are still unvaccinated against Covid-19! Because they don't want to be vaccinated, they think it's a breach of their rights, they don't believe it works, or they just can't be bothered. So of course Joe Biden's patience is wearing thin as he describes it which is why he has now issued an executive order telling all companies with more than 100 employees to give their staff mandatory jabs or weekly Covid tests. That has to be right. Before the winter sets in everyone has to be vaccinated. But Biden has already been attacked by Mike Pence, former vice president, for doing something which he claims is totally un-American. Oh for God's sake, needs must whether it's un-American or not. If there are 80 million Americans out there refusing to get the jab then they need to be mandated to get the vaccine not just for their safety but for everyone's else safety. Biden is right and Pence deserves never to stand for office again. Covid is not going to go away unless everyone accepts that brilliant scientists have developed a whole variety of vaccines that work and that it's sheer madness and irresponsibility not to queue up and get jabbed. If the latest decision by Biden fails to do the trick then America will be looking towards a very bleak winter.