The virus had more than a year to stumble upon mutations that let it more effectively enter human cells and evade our immune systems. Now, we have Delta: roughly twice as transmissible as earlier strains of the virus, and possibly as contagious as chickenpox.
As vaccine rates stagnate in the U.S., the highly transmissible Delta variant now accounts for more than 82 percent of new cases. "The war has changed," writes the Centers for Disease Control and Prevention in an internal document leaked to the Washington Post.
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