...But the new vaccines protect against two different strains of Covid-19: the original strand and the latest Omicron variant, BA.5. BA.5 just emerged in August, and it’s spreading extremely fast–it now accounts for 88% of the cases in the U.S. The FDA authorized these “bivalent” boosters on August 31. My main point today is to explain how this happened so quickly, and why it didn’t involve many months of clinical trials the way that the original vaccines did. Some people have expressed suspicion about the speed with which these boosters appeared, but those suspicions are entirely unfounded.... (W)e change the...