Chadi and Caroline join TWiV to describe the potential epidemiological and evolutionary impacts of vaccine nationalism, and their modeling which emphasizes the importance of rapid equitable vaccine distribution for global control of the pandemic.

Shane Crotty returns to TWiV to review the immunology of COVID-19, including differences between infection and vaccination, increased breadth of antibodies after infection followed by vaccination, the roles of T cells, and whether booster vaccinations are needed.

The meteorologicomaniacs discuss the COVID-19 pandemic global death toll, effectiveness of vaccines against the delta variant, and how analysis of ancient viral DNA reveals that two pathogenic human viruses were brought into Mexico during the transatlantic slave trade.

Ron Fouchier explains why increased transmission of SARS-CoV-2-variants has not been demonstrated, and their ability to displace ancestral variants is due to greater fitness, much like influenza virus antigenic variation leads to better fitness and replacement of previously circulating variants.