No. The Delta variant has been around since October 2020 where it was initially detected in India. This predates the vaccines going public. https://www.nature.com/articles/s41586-021-03777-9 The Delta variant thrives compared to previous variants because it is more virulent. The R0 value is higher than the previous strains. If a pathogen kills the victims too quickly or has simplistic transmission paths, no matter how deadly, it will kill the hosts too quickly to spread. It needs to be airborne and take several days to make the host ill. That's what most cold viruses are. These coronaviruses are ever so slightly more deadly than they previously were (lab created to be deadlier looks like a probable explanation for why it is deadlier). Just a slight tweak in mortality rates from these viruses can greatly increase the number of people they kill each flu and cold season. A virologist knows this. You only need 2 tweaks to a cold virus to make it much deadlier than previous strains: Make it spread faster (increase the R0 value) Make it kill more often (increase the IFR). On paper, the Delta Variant is not much different than the previous ones. But the R0 is slightly higher than the previous versions. There's speculation that it also kills slightly more people (higher IFR). But that's all you really need to turn a virus much more deadly - it is a game of numbers. Add on top of that, the Delta Variant evades both vaccines (significantly) and natural immunity (significant but not nearly as much as it can evade the vaccines). Pretty shitty outcome.