The delta variant was first identified in India. It is a major reason India experienced an unprecedented spike in cases and deaths during its recent second wave. Why is the delta variant so much worse? Any variant must be judged on three dimensions: Is it more contagious? Is it more deadly? And does it escape either natural or vaccine-induced immunity? The delta variant may be one of the first triple threats across all those factors. The emerging and relatively strong evidence is that delta is far more contagious than any other variant recorded to date. It appears to be more deadly to those infected, and it appears to cause more infections among people with immunity than many other variants. So what’s the impact of a covid-19 variant that is much more contagious, possibly more deadly and that may be causing more breakthrough infections in those who are only partly protected? Well, again, let’s look at the evidence: In India, the delta variant flattened the health-care system and caused hundreds of thousands of deaths. In Britain, it has quickly become the dominant strain and has caused the number of daily infections to triple in just the past month. And it has arrived here. As of Wednesday, the delta variant accounts for 10 percent of U.S. infections and is doubling its share of new cases every two weeks. At this rate, delta will become our dominant strain in the next month to six weeks.