Protection against infection after two doses is not looking very good. “Omicron was a huge jump in evolution,” says Jesse Bloom, an evolutionary virologist at the Fred Hutchinson Cancer Research Center, in Seattle. In what seems to be just a few months, the virus has changed as much as Bloom says he and many researchers expected it to change “over the span of four or five years.” In a slew of recent lab studies, the potency of antibodies that can neutralize the virus dropped anywhere from five- to sevenfold against “pseudoviruses” that have been engineered to carry Omicron’s spike mutations to 41-fold in a study with live Omicron viruses, which is the gold standard. (In the Beta and Delta variants, we saw drops of about six- and threefold compared with the original virus, respectively.) A 41-fold drop in neutralizing antibody activity after two doses does not mean a 41-fold drop in vaccine effectiveness. The real-world impact is hard to predict, but the effect is big enough that protection against infection might be quite low, says Florian Krammer, a virologist at Mount Sinai’s Icahn School of Medicine. “I think you’re dealing with a variant that has no problem infecting vaccinated individuals,” he says.
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