Why vaccines haven't halted COVID in the US

America's luck when it comes to COVID-19 seems to have changed, and then changed back again. US President Joe Biden made it very clear from the outset that handling the pandemic was number one on his to do list. But after some early wins against the virus, COVID transmission is on the rise again. So what's gone wrong? And can Biden turn it around before it becomes a fourth wave? Featured: Dan Diamond, National Health Reporter, The Washington Post